<<

. 2
( 10)



>>

demonstration of free intraperitoneal air following bowel
is preferred.
perforation or of bowel dilatation and air/¬‚uid levels in intestinal
Conversely, barium is safer than water-soluble contrast medium in
obstruction (¬g. 2.3).
the lungs and in cases where aspiration is suspected, barium should
It is important to ¬nd out about the position of the patient
be used. This underlines the importance of providing the radiologist
when the ¬lm was taken. A patient needs to be erect for at least
with the relevant clinical information (¬g. 2.5).
10 minutes to permit any free air to accumulate in the typical
When interpreting contrast medium studies of the GI tract, such as
location below the diaphragm. Lateral “shoot-through” or
small bowel follow-through studies and barium enemas, a number of
decubitus ¬lms (the latter with the patient lying on one side)
common principles should be applied.
can help to establish the presence of a free intraperitoneal air or
Always try to ¬nd out by what route the contrast medium was
pneumoperitoneum.
administered. For instance, a rectal or nasojejunal tube is often visible
on the ¬lm.




18
How to interpret an image adam w. m. mitchell


(b)
(a)




(d)
(c)




Fig. 2.4. Multiple views
to exclude a fracture of
the scaphoid bone.
Normal examination.




19
How to interpret an image adam w. m. mitchell


Fig. 2.6. Intravenous
urogram (IVU).
15-minute The renal
collecting systems
Distal oesophagus
ureters and bladder are
Barium in gastric fundus
opaci¬ed with iodinated
Anterior rugal fold contrast.
Lesser curvature

Outline of
duodenal cap
Posterior rugal folds


Body of stomach


Pyloric gastric Greater
intrum curvature



Fig. 2.5. Supine barium meal examination demonstrating rugal folds. The anterior
surface of the stomach can be differentiated from the posterior in the supine
position due to pooling of barium around the posterior folds.




Establish which part of the bowel has been opaci¬ed and how far
along the GI tract the contrast medium has travelled. If only the large
bowel has been opaci¬ed, the study is almost certainly a barium
enema.
It may also be useful to establish the position of the patient when
the views were taken. ¬‚uid levels and bony landmarks are useful for Blood within the
aorta opacified
Bowel loop
this purpose. with contrast
containing
medium
water
Air is often used as a second contrast medium with barium and
these examinations are termed “double-contrast” studies. The
distension provided by air insuffation or after swallowing effervescent
tablets, as appropriate, results in better mucosal detail.
Bowel preparation is very important in lower GI tract studies as
fecal contamination may degrade a barium enema by obscuring a
Fig. 2.7. CT scan upper abdomen, following intravenous contrast medium and
genuine abnormality or by generating artifactual “¬lling defects.” It
water by mouth.
may help if such defects alter their position between ¬lms, con¬rming
their fecal nature.
Similarly, the stomach must be empty of food before a barium meal.
Therefore, the right side of the patient is on the left side of the image,
when the images have been acquired with the patient supine.
Contrast studies of the kidney and urinary tract
Oral and intravenous contrast media are often used during a CT
The most common renal contrast medium study performed is the scan. Oral contrast medium is usually a water-soluble substance, such
intravenous urogram or “IVU.” After a “control” (plain), ¬lm has been as gastrogra¬n. This opaci¬es the bowel lumen, which becomes hyper-
taken, iodinated contrast medium is injected intravenously and dense (white). The bowel can then be differentiated from other soft
further images are then taken as the contrast medium is excreted tissues. Be aware, though, that it is rare for every loop of bowel to
through the kidneys. It is important to study the control ¬lm carefully be opaci¬ed, and unopaci¬ed loops may still cause confusion. More
to look for calci¬cation, which may subsequently be obscured by recently, water has used as an alternative oral contrast medium. This
contrast medium. appears of intermediate density on CT scans, and gives very good
IVU ¬lms are taken at different time intervals, which are marked on delineation of the higher density bowel mucosa adjacent to it (¬g. 2.7).
the ¬lm, and an abdominal compression band may be applied to opti- Intravenous contrast medium can be identi¬ed on CT scans by the
mize urinary tract opaci¬cation (¬g. 2.6). density of the blood within the blood vessels. The aorta is easiest to
identify and will appear whiter than the surrounding soft tissues when
contrast medium has been used. It is usual for images to be annotated,
Computed tomography
albeit often rather cryptically with “ C,” to inform the radiologist that
The principles of computed tomography (CT) have been discussed in contrast medium has been administered. Use all the clues available!
the previous chapter. Several points should be remembered in the The radiodensity of soft tissues will vary depending on the time
interpretation of the images. interval between the administration of the contrast medium and the
The images are usually acquired in the axial plane and are viewed scan. Scans performed within 20“40 seconds of the injection, termed
as though looking at the patient from the feet up towards the head. the arterial phase, will show the aorta very white, but the solid organs

20
How to interpret an image adam w. m. mitchell


(a) (b)




Fig. 2.8. CT chest. The same image displayed on (a) soft tissue and b) lung windows Mediastinal detail is better shown in (a), pulmonary detail in (b).


(a) (b)




Fig. 2.9. MRI brain; T1 weighted coronal scans (a) before and (b) after intravenous gadolinium DTPA. Malignant intracerebral tumour. Breakdown of the blood“brain
barrier has resulted in gadolinium enhancement of the solid elements of the tumor.




will not appear to be very different in density from the non-enhanced Since it is a digital technique, CT images can be viewed on different
study. Delayed imaging, at 50“70 seconds, will show the organs to be “windows.” This means that the gray scale of the image is altered so
much brighter. Focal lesions within the liver and spleen are much that some tissues are better seen than others (¬g. 2.8). The most fre-
easier to see on these later images. quently used windows are for the soft tissues and the lungs. Be sure to
As in conventional radiography, calci¬cation can be obscured by look at the appropriate images, so as not to miss important details in
the presence of contrast medium, and is best evaluated on a non- the lungs or mediastinum. It is also valuable to view the images on
enhanced study. bone windows, to evaluate the presence of focal bone lesions.

21
How to interpret an image adam w. m. mitchell


CT images are often of varying slice thickness. The slice thickness is T1 weighted images show fat as very bright, so evaluation of the sub-
written on the images. Thin slices give ¬ner detail but these scans cutaneous tissues is helpful in identifying the weighting. There are
take longer and involve more radiation dose to the patient. Thicker many other, often complicated, sequences, but a discussion of these is
slices can be prone to artifact. High-resolution images of the chest give beyond the scope of this introduction.
very ¬ne detail of the lungs. Gadolinium DTPA is the standard intravenous contrast medium
used in MR imaging. It is seen best on T1 weighted images and the
principles involved are very similar to those in CT contrast medium
Magnetic resonance imaging
enhancement (¬g. 2.9).
Magnetic resonance imaging (MRI) is the mainstay of neuroimaging Other contrast media are used in the evaluation of the hepatobiliary
and perhaps also musculoskeletal imaging and is becoming increas- system and of lymph nodes. These agents alter the signal returned
ingly popular in the evaluation of the hepatobiliary system and pelvis. from the soft tissues, to increase the conspicuity of focal lesions.
The principles of magnetic resonance have been discussed previously.
The interpretation of the images can be daunting at ¬rst, partly due to
Nuclear medicine imaging
the sheer number involved. Images can be acquired in any plane but
the commonest are the sagittal, axial and coronal (the orthogonal) Nuclear medicine images are functional studies and, as such, are inter-
planes. It is vital to orientate oneself carefully, by studying the anatomy preted differently. Renal imaging is acquired from the back, so that
of the image, before proceeding in the interpretation of the study. the right kidney is on the right of the image. Most other images are
The commonest MR images are T1 or T2 weighted. T2 weighted acquired from the front. The agent used is almost invariably marked
images show water as white. Most images will show cerebrospinal on the ¬lm and gives important clues to the evaluation of the study.
¬‚uid, which is mainly water, somewhere on the image and this is Other helpful clues may be the time of the image acquisition and the
a useful reference point to decide on the weighting of the scan. use of other agents such as diuretics.




22
Section 2 The thorax

Chapter 3 The chest wall and ribs


J O NAT H A N D . B E R RY
and S U J A L R . D E S A I




Introduction projection will become mandatory. Occasionally, when the anatomical
localization of lung abnormalities is dif¬cult to discern, a lateral view
Radiological investigation of the chest is a common occurrence in
of the chest will be requested.
clinical practice. Thus, a working knowledge of thoracic anatomy, as
seen on radiological examinations, is crucial and has an important
Computed tomography (CT)
bearing on management. The present chapter considers the anatomy
of the thorax as related to imaging. The appearances of the thoracic Computed tomography (CT) is a specialized X-ray technique, which
structures on plain radiography and computed tomography (which produces cross-sectional (or axial) images of the body. The basic com-
together constitute two of the most frequently requested radiological ponents of a CT machine are an X-ray tube, a series of detectors (sited
tests) will be discussed in most detail. diametrically opposite the tube), and computer hardware to recon-
For the purposes of anatomic description, the thorax is bounded by struct the images. When reviewing CT images, the observer must
the vertebral column posteriorly, together with the ribs, intercostal imagine that the cross-sectional images are being viewed from below;
muscles, and the sternum antero-laterally. The superior extent of the thus, structures on the left of the side of the subject will be on the
thorax (lying roughly at the level of the ¬rst vertebral body) is the observer™s right.
narrowest point and, through the thoracic inlet, the contents of the The main advantage of CT, over plain chest radiography, is that
chest communicate with those of the neck. Inferiorly, the thorax is there is no superimposition of anatomical structures. Furthermore,
separated from the abdomen by the diaphragm. because CT is very sensitive to difference in density of structures and
the data are digitized, images may be manipulated to evaluate sepa-
rately at the pulmonary parenchyma, mediastinal soft tissues, or the
Commonly used techniques for imaging the chest
ribs and vertebrae (Fig. 3.2).
Imaging of the thorax rightly is regarded as an important component
of clinical investigation. For most patients, the plain chest radiograph
will be the ¬rst (and sometimes only) radiological test that is required.
In more complex cases, the clinician will request computed tomogra-
phy (CT). The technique of magnetic resonance imaging (MRI), which
is well established in other spheres of medicine, has relatively few
applications for the routine investigation of chest diseases and will
Fig. 3.1. Standard
not be discussed in any detail in this chapter except where points of postero-anterior chest
anatomical interest can be illustrated. radiograph. The heart
(asterisk) is of normal
Chest radiography size; the ratio of the
transverse diameter
The standard projection for imaging of the chest is the postero-ante-
of the heart to the
rior (PA) or “frontal” view, in which the patient faces the ¬lm plate
maximal transverse
*
and the X-ray tube is sited behind the patient. On a frontal projec-
diameter of the
tion, because the heart is as close as possible to the X-ray ¬lm plate, thorax (also called
magni¬cation is minimized (Fig. 3.1). However, in some patients, the cardiothoracic ratio)
who are unable to be positioned for the PA view, the antero-posterior is less than 50%.




Applied Radiological Anatomy for Medical Students. Paul Butler, Adam Mitchell, and Harold Ellis (eds.) Published by Cambridge University Press. © P. Butler,
A. Mitchell, and H. Ellis 2007.

23
jonathan d. berry and sujal r. desai
The chest wall and ribs


(a) (b)




Fig. 3.2. Two CT images at exactly the same anatomical level manipulated to show (a) the lung parenchyma; the pulmonary vessels are seen as white, branching
linear structures (thin arrows). (b) Soft-tissue settings showing the midline structures of the mediastinum, ribs (arrowheads) and muscles of the chest wall (thick
arrows) but not the lung parenchyma.



(a) (b)



UL




*


LL




Fig. 3.3. Targeted views of (a) frontal radiograph to show the horizontal (minor) ¬ssure (arrows) and (b) lateral projection showing the lower halves of both oblique
¬ssures (arrows). The horizontal ¬ssure is also noted on this view (arrowhead). The lower lobes (LL) lie behind and below whereas the upper lobes (UL) are above
and in front of the oblique ¬ssures. The middle lobe (asterisk) is located between the horizontal and relevant oblique ¬ssure.



Anatomy of the chest The horizontal ¬ssure is seen readily on a standard PA radiograph as
a thin line crossing from the lateral edge of the hemithorax to the
The lungs and airways
hilum. On a lateral view of the chest, both the oblique ¬ssures may be
Each lung occupies, and almost completely ¬lls, its respective
visualized, running obliquely in a cranio-caudal distribution (Fig. 3.3);
hemithorax. On the right, there are three lobes (the upper, middle,
the horizontal ¬ssure can also be seen running forward from the
and lower) and on the left, two (the upper and lower); incidentally, the
oblique ¬ssure Occasionally, accessory ¬ssures will be seen on a chest
lingula generally is considered a part of the left upper lobe. The upper
radiograph.
and lower lobes, on each side, are separated from each other by the
The lungs are lined by two layers of pleura, which are continuous at
oblique ¬ssure. On the right, the middle lobe is divided from the
the hila. The parietal pleura covers the inner surface of the chest wall
upper by the horizontal ¬ssure. By contrast, it should be noted that,
whereas the visceral layer is closely applied to the lung surface. A
on the left, there is no ¬ssural division between the left upper lobe
small volume of “normal” pleural ¬‚uid is generally present within the
and lingula. On a PA chest radiograph, the oblique ¬ssure is generally
pleural cavity to facilitate the smooth movement of one layer over the
not visible. Futhermore, because the upper lobe lies anteriorly, most
other during breathing. In the absence of disease, the pleural layers
of the lung that is seen on the frontal view will be the upper lobe.

24
jonathan d. berry and sujal r. desai
The chest wall and ribs


Fig. 3.6. Targeted and
will not be seen on chest radiograph. However, because of the supe-
magni¬ed view of the
rior contrast resolution, the normal pleura may be visualized on CT
tracheal carina (asterisk).
images (Fig. 3.4).
The right main bronchus
The trachea is a vertically orientated tube (measuring approxi-
(thin arrows) is shorther
mately 13 cm in length), which commences below the cricoid cartilage and more vertically
and extends to the approximate level of the sternal angle where is orientated than the left
bifurcates. In cross-section the outline of the trachea may vary from (thick arrows).
being oval to a D-shape, depending on the phase of breathing cycle.
Anteriorly and laterally, the trachea is bounded by hoops of hyaline
cartilage but posteriorly there is a relatively pliable membrane. On a
chest radiograph, the trachea is seen as a tubular region of lucency in
*
the midline, as it passes through the thoracic inlet (Fig. 3.5). At the
level of the aortic arch, there may be slight (but entirely normal) devi-
ation of the trachea to the right. At the level of the carina, the trachea
divides into right and left main bronchi; the former is shorter, wider
and more vertically oriented than its counterpart on the left (Fig. 3.6).
Each main bronchus gives rise to lobar bronchi, which divide to
supply the bronchopulmonary segments in each lobe. Individual bron-
chopulmonary segments are not readily identi¬ed (on chest radiogra-
phy or CT) but it is worth revising the anatomy because segmental airways and arteries can be seen particularly well on CT images and
such information may be important to clinicians. On the right, there
are ten segments (three in the upper lobe, two in the middle and ¬ve
in the lower lobe), whereas on the left there are nine (three in upper
lobe, two in the lingula and four in the lower lobe (Fig. 3.7).

The mediastinum
For descriptive purposes, the mediastinum has always been thought
of in terms of its arbitrary compartments. Thus, the superior medi-
astinum is considered to lie above a horizontal line drawn from the
lower border of the manubrium, the sternal angle or angle of Louis,
to the lower border of T4 and below the thoracic inlet (Fig. 3.8). The
inferior compartment, lying below this imaginary line (and above the
hemidiaphragm) is further subdivided: the anterior mediastinum lies
in front of the pericardium and root of the aorta. The middle medis-
tinum comprises the heart and pericardium together with hilar struc-
tures, whereas the posterior mediastinum lies between the posterior
aspect of the pericardium and the spine. Whilst the above division is
entirely arbitrary, the validity of remembering such a scheme is that
the differential diagnosis of mediastinal masses is re¬ned by consider-
ing the localization of a mass in a particulary mediastinal compart-
ment. The main contents of the different mediastinal compartments
Fig. 3.4. Targeted view of the left lower zone on CT showing normal thin pleura
are listed in Table 3.1. Some of the important components of the medi-
(arrow).
astinum are discussed below:


The esophagus
The esophagus extends from the pharynx (opposite the C6 vertebral
body) through the diaphragm (at the level of T10) to the gastro-
esophageal junction and measures approximately 25 cm in length.
In its intrathoracic course the esophagus is a predominantly a left-
AA
sided structure, a feature which is readily appreciated on CT images
Fig. 3.5. PA chest
(Fig. 3.9). By contrast, the esophagus is normally not visible on a
showing the
standard PA radiograph, and radiographic examination requires
characteristic tubular
the patient to drink a radioopaque liquid (i.e., a barium
lucency of the trachea
suspension).
(arrowheads). The
normal and minimal
deviation of the trachea
The thymus
to the right is noted at
The thymus is a bilobed structure, which is posititoned in the space
the level of the aortic
between the great vessels (arising from the aorta) and the anterior
arch (AA).


25
jonathan d. berry and sujal r. desai
The chest wall and ribs



Left apical bronchus
Right upper
lobe bronchus
Right apical Left posterior
Apicoposterior
bronchus bronchus
bronchus


Left anterior
Right posterior 11 bronchus
bronchus
Left upper
1
lobe bronchus
12
Right anterior Superior lingular
R L
2
bronchus bronchus
13
RUL
LUL
3 14 15
BI
Lingular
Right middle
16
brochus Inferior lingular
lobe bronchus
4 17 bronchus
LLL
Apical 17
4
ML bronchus
RLL of lower
Lateral bronchus of
5 lobe
right middle lobe 6 10 18 Left anterior
7 basal bronchus
Medial basal
8
(cardiac)
19
Medial bronchus of 9 bronchus
right middle lobe 20
Right anterior
basal bronchus
Right lateral
Left lateral
basal brochus Left posterior
basal bronchus
basal bronchus

Right posterior
basal bronchus


Fig. 3.7. Schematic diagram illustrating the segmental anatomy of the bronchial tree (reproduced with
permission from Applied Radiological Anatomy, 1st edn, Chapter 6, The chest, p. 129, Fig. 11(f), ed. P.
Butler; Cambridge University Press).

Fig. 3.8. Lateral
ta b l e 3 . 1 . American Thoracic Society de¬nitions of regional nodal
radiograph
stations
demonstrating the
anterior (A), middle (M),
X Supraclavicular nodes
posterior (P) and
Right upper paratracheal nodes: nodes to the right of the midline of
2R
superior (S) mediastinal
the trachea, between the intersection of the caudal margin of the
compartments.
innominate artery with the trachea and the apex of the lung
Left upper paratracheal nodes: nodes to the left of the midline of the
2L
trachea, between the top of the aortic arch and the apex of the lung
Right lower paratracheal nodes: nodes to the right of the midline of
4R
the trachea, between the cephalic border of the azygos vein and the
intersection of the caudal margin of the brachiocephalic artery with
the right side of the trachea
Left lower paratracheal nodes: nodes to the left of the midline of the
4L
trachea, between the top of the aortic arch and the level of the carina,
medial to the ligamentum arteriosum
Aortopulmonary nodes: subaortic and paraaortic nodes, lateral to the
5
ligamentum arteriosum or the aorta or left pulmonary artery,
proximal to the ¬rst branch of the left pulmonary artery
Anterior mediastinal nodes: nodes anterior to the ascending aorta or
6
the innominate artery
Subcarinal nodes: nodes arising caudal to the carina of the trachea but
7
chest wall. The volume of the thymus normally changes with age: in
not associated with the lower lobe bronchi or arteries within the lung
the newborn, for example, the thymus may occupy the entire volume
Paraesophageal nodes: nodes dorsal to the posterior wall of the
8
of the mediastinum anterior to the great vessels (Fig. 3.10). With age, trachea and to the right or left of the midline of the esophagus
the thymus initially hypertrophies, but after puberty there is progres- Right or left pulmonary ligament nodes: nodes within the right or left
9
sive atrophy, such that in normal adults, the normal thymus is barely pulmonary ligament
Right tracheobronchial nodes: nodes to the right of the midline of the
discernible. 10R
trachea, from the level of the cephalic border of the azygos vein to the
origin of the right upper lobe bronchus
The hilum
Left tracheobronchial nodes: nodes to the left of the midline of the
10L
The hilum can be considered to be the region at which pulmonary trachea, between the carina and the left upper lobe bronchus, medial
vessels and airways enter or exit the lungs. The main components of to the ligamentum arteriosum
each hilum are the pulmonary artery, bronchus, veins, and lymph Intrapulmonary nodes: nodes removed in the right or left lung specimen,
11
nodes. On a frontal radiograph, the right hilum may be identi¬ed as a plus those distal to the main-stem bronchi or secondary carina
broad V-shaped structure; the left hilum is often more dif¬cult to
From Glazer et al. (1985).
identify con¬dently (Fig. 3.11). A useful landmark for the radiologist,

26
jonathan d. berry and sujal r. desai
The chest wall and ribs


primitive aortae; with subsequent septation and coiling, the character-
istic asymmetric con¬guration of the adult heart is attained. The peri-
cardium, which like the pleura is a two-layered membrane, encases
the heart; the inner (or visceral) pericardium is applied directly to the
* myocardium except for a region that re¬‚ects around the pulmonary
veins. The outer (parietal) pericardium is continuous with the adventi-
tial ¬brous covering of the great vessels. Inferiorly, the parietal peri-
cardium blends with the central tendon of the diaphragm. As with the
pleura, the potential space between the visceral and parietal peri-
cardium (the pericardial sac) is not normally visible on plain radi-
ographs. Again, because of the superior contrast resolution of CT, the
normal pericardial lining may be identi¬ed on axial images.
In normal subjects there are four cardiac chambers (the paired atria
and ventricles). Deoxygenated blood is normally delivered to the right
atrium via the superior vena cava (from the upper limbs, thorax, via the
azygos sytem, and the head and neck), the inferior vena cava (from the
Fig. 3.9. Axial CT image on soft tissue window settings at the level of the great
lower limbs and abdomen), and the coronary sinus (from the
vessels. The oesophagus (arrow) can seen lying just to the left of the midline
and posterior to the trachea (asterisk). myocardium). The right atrium is separated from its counterpart on the
left by the inter-atrial septum which, with the changes in pressure that
Fig. 3.10. CT of the occur at or soon after birth, normally seals; a depression in the intera-
normal thymus in an trial septum marks the site of the foramen ovale in the fetal heart. The
infant. There is a well-
right atrium is a “border-forming” structure on a PA radiograph that is
de¬ned mass (thin
immediately adjacent to the medial segment of the right middle lobe, a
arrows) in the superior
feature that is readily appreciated on CT images (Fig. 3.12). The right
mediastinum. Note how
ventricle communicates with the atrium via the tricuspid valve.
the mass conforms to
Deoxygenated blood leaves the right ventricle through the pulmonary
the outline of some the
major vessels (the aorta valve and enters the pulmonary arterial tree. Because the right ventricle
[thick arrow] and is an anterior chamber, it does not form a border on the standard PA
superior vena cava
radiograph but the outline of the chamber is visible on a lateral radi-
(arrowhead)) in the
ograph. The left atrium is a smooth-walled chamber and is posteriorly
mediastinum, and does
positioned. Oxygenated blood enters the atrium from the paired pul-
not displace them.
monary veins on each side and exits via the mitral valve to the left ven-
tricle from where blood is delivered into the systemic circulation. As on
the right, there is a left atrial appendage (sometimes referred to as the
auricular appendage), which may be the only part of the normal atrium
that is seen on the frontal radiograph; conversely, the wall of the left
atrium is easily identi¬ed on a lateral radiograph.
The left ventricle is the most muscular cardiac chamber and is a
roughly cone-shaped structure whose axis is oriented along the left
anterior oblique plane. On a frontal chest radiograph, the left ventricle
accounts for most of the left heart border. It is worth mentioning at this
point that the widest transverse diameter of the heart (extending from
the right (formed by the right atrium) to the left margin) is an impor-
tant measurement on the frontal radiograph: as a general rule, the
Fig. 3.11. Targeted and magni¬ed view from PA chest radiograph clearly shows
transverse diameter should be less than half the maximal diameter of
the hilar vessels. The right and left hilar points (where the upper lober veins
the chest (this measurement is called the cardiothoracic ratio).
apparently “cross” the lower lobe artery) are indicated (arrows).



on the PA radiograph, is the so-called “hilar point” which, whilst not
being a true anatomical structure, is the apparent region where the
upper lobe pulmonary veins meet the lower pulmonary artery. In Fig. 3.12. Axial CT image
RA
normal subjects, the hilar point is sited roughly between the apex and on lung parenchymal
window settings
the base of the hemithorax: in some patients, signi¬cant elevation or
showing the relationship
depression of the hilar point will be the only clue to the presence of
of the middle lobe (lying
volume loss in the lungs.
anterior to the horizontal
¬ssure [arrows]),
The heart particularly its medial
In the embryo, the heart is one of the earliest organs to develop, segment and the right
following fusion of two parallel tubular structures known as the atrium (RA).


27
jonathan d. berry and sujal r. desai
The chest wall and ribs


(a) (b) Catheter
Catheter Atrial
branch Conus branch
Atrial branch




RV free wall branches




RV free
wall branch
Inferior LV
Superimposed posterior
free wall
Posterior descending artery descending and
branches
LV free wall branches

Fig. 3.13 (a), (b). Coronary angiogram demonstrating the left and right coronary arteries (reproduced with permission from Applied Radiological Anatomy, 1st edn,
Chapter 7, The heart and great vessels, p. 165, Figs. 24 and 25; ed. P. Butler, Cambridge University Press).



Fig. 3.14. Digital
Oxygenated blood normally enters the ventricle from the left RCC
subtraction angiogram
atrium via the mitral valve and is pumped into the systemic circula- LSC showing the ascending
tion through the aortic valve. Just above the aortic valve there are LCC (AA) and descending
three focal dilatations, called the sinuses of Valsalva. The right coro- (DA) aorta. Note that the
RS
nary artery originates from the anterior sinus, whilst the left posterior brachiocephalic artery
sinus gives rise to the left coronary artery; the coronary circulation is (B) bifurcates into the
right subclavian (RS) and
described as either right (the most common arrangement) or left B
right common carotid
dominant depending on which vessel supplies the posterior diaphrag-
(RCC) arteries; the left
matic region of the interventricular septum and diaphragmatic
AA DA common carotid (LCC)
surface of the left ventricle. The right coronary artery usually runs and left subclavian (LSC)
forward between the pulmonary trunk and right auricle. As it also arise from the
descends in the atrioventricular groove, branches arise to supply the aortic arch.
right atrium and ventricle. At the inferior border of the heart, it con-
tinues and ultimately unites with the left coronary artery. The larger
left coronary artery descends between the pulmonary trunk and left pericardium and includes three focal dilatations, the sinuses of
auricle, and runs in the left atrioventricular groove for about 1 cm Valsalva (described above) above the aortic valve lea¬‚ets. The ascend-
before dividing into the left anterior descending (interventricular) ing aorta continues upward and to the right for approximately 5 cm to
artery and the circum¬‚ex arteries. In around one-third of normal sub- the level of the sternal angle. The arch lies inferior to the manubrium
jects, the left coronary artery will trifurcate and in such cases there is sterni and is directed upward, inferiorly, and to the left. The arch ini-
a “ramus medianus” or “intermediate” artery between the left ante- tally lies anterior to the trachea and esophagus, but then extends to
rior descending and circum¬‚ex arteries supplying the anterior left the bifurcation of the pulmonary trunk. The three important branches
ventricular wall. The venous drainage of the heart is via the coronary of the aortic arch are the brachiocephalic artery, the left common
sinus (which enters the right atrium) and receives four main tribu- carotid artery, and the left subclavian artery, all of which are readily
taries: the great cardiac vein, middle cardiac vein, small cardiac vein, visible on angiographic studies and CT (Fig. 3.14). Variations to this
and left posterior ventricular vein. A smaller proportion of the venous normal pattern of branching occur in approximately one-third of sub-
drainage is directly into the right atrium via the anterior cardiac veins jects; the most common variant is that in which the left common
that enter the anterior surface of the right atrium. As might be imag- carotid arises from the brachiocephalic artery.
ined, the normal cardiac circulation is not seen on standard radi- By convention, the descending aorta begins at the point of attach-
ographic examinations. However, the injection of intravenous contrast ment of the ligamentum arteriosum to the left pulmonary artery
via a coronary artery catheter (inserted retrogradely via the femoral (roughly at the level of T4). The descending aorta passes downward in
artery) will render the vessels visible (Fig. 3.13). An alternative the posterior mediastinum on the left to the level of T12, where it
approach (which has only become possible since the advent of “fast” passes through the diaphragm and into the abdomen. Within the
CT scanning machines) is for the cardiac circulation to be imaged fol- thorax, the descending aorta gives rise to the intercostal, subcostal
lowing a peripheral injection of contrast. More recently, there has arteries, bronchial, esophageal, spinal, and superior phrenic arteries.
been considerable interest in the imaging of the heart and its circula-
Pulmonary arteries
tion using magnetic resonance imaging.
At its origin from the right ventricle, the pulmonary conus or trunk is
The aorta invested by a pericardial re¬‚ection. The main divisions of trunk are
The intrathoracic aorta can conveniently be considered in four parts: the left and right pulmonary arteries. The right pulmonary artery
the root, the ascending aorta, the arch, and the descending aorta. passes in front of the right main bronchus and behind the ascending
The root comprising the initial few centimeters, is invested by aorta. Anteriorly, the right superior pulmonary vein crosses the right

28
jonathan d. berry and sujal r. desai
The chest wall and ribs


Fig. 3.15. CT image just
The thoracic cage
below the level of the
tracheal carina. The right Ribs, sternum and vertebrae
PT
main pulmonary artery
AAo The thorax is roughly cylindrical in shape and shielded by the ribs,
(RtPA) passes in front of
thoracic vertebrae, and the sternum. All 12 pairs of ribs are attached
the right main bronchus
RtPA posteriorly to their respective vertebral bodies. In addition, the upper
(arrow). The left
*
seven pairs attach anteriorly to the sternum via individual costal carti-
LtPA pulmonary artery arches
DAo lages. The eighth, ninth and tenth ribs effectively are attached to each
over the left main
bronchus (asterisk). other and also the seventh rib by means of a “common” costal carti-
AAo ascending aorta; lage. With age, the costal cartilages may calcify and are then readily
PT pulmonary trunk;
visible on a frontal radiograph. The two lowermost ribs (the 11th and
LtPA left basal
12th) are described as “¬‚oating” since they have no anterior attach-
pulmonary artery.
ment. An interesting variation to the normal arrangement (occuring
in around 6% of the population) is the so-called “cervical” rib, which
articulates with a cervical, instead of a throracic vertebral body
(Fig. 3.16). Cervical ribs may be uni- or bilateral. Occasionally, there
main artery (Fig. 3.15). At the hilum, the artery divides into the upper
will simply be a ¬brous band but, when calci¬ed, the appearance of a
and lower divisions, from which the lobar and segmental branches
“true rib” will be seen. Some cervical ribs are symptomatic because of
orginate; It is important to remember that arterial branching (unlike
the potential for compression of the subclavian artery and ¬rst tho-
the pulmonary veins) closely follows the branching of the airways.
racic nerve root.
The left main pulmonary artery passes posteriorly from the pul-
The sternum can be considered to comprise three components: the
monary trunk and then arches over the left main bronchus. As with
manubrium sterni, the body of the sternum, and the xiphoid process
the coronary arteries, the pulmonary circulation is visualized opti-
(or xiphisternum). The manubrium is the uppermost and widest
mally after the injection of intravenous contrast, as in conventional
portion, which articulates laterally with the clavicles and also the ¬rst
pulmonary angiography (a technique seldom performed in modern
and upper part of the second costal cartilages; inferiorly, the
radiology departments) or on CT images. The venous drainage of the
manubrium articulates with the body of the sternum. On a conven-
lungs is via the left and right pulmonary veins, two on each side,
tional frontal chest radiograph, the bulk of the manubrium is gener-
which enter the left atrium beneath the level of the pulmonary arter-
ally not visible. However, the articulation of the manubrium with the
ies. Occasionally, the veins can be seen to unite prior to their entry
clavicles (the manubrio-clavicular joint) can be seen. By contrast, on a
into the left atrium.
lateral radiograph the manubrium can be clearly identi¬ed. The body
It should be remembered that, in addition to the main pulmonary
of the sternum is a roughly rectangular structure which has a notched
arterial supply, there is a bronchial circulation originating from the
lateral margin, where it articulates with the costal cartilages of the
systemic circulation. The most common arrangement is of a single
third to seventh ribs. The xiphoid is the most inferior portion of the
right bronchial artery (usually arising from the third posterior inter-
sternum and prinicipally consists of hyaline cartilage that may
costal) and two left bronchial arteries (originating from the descend-
become ossi¬ed in later life.
ing thoracic aorta). However, there is considerable normal variation.
The thoracic vertebrae provide structural support to the thorax in
There are two groups of bronchial veins: the deep veins taking blood
both the axial (vertical) and, through the attachment with ribs and
from the lung parenchyma and draining into the pulmonary veins.
muscles, the coronal and sagittal planes. Whilst individual vertebrae
The super¬cial bronchial veins receive blood from the extrapul-
are rigid, their articulations mean there is considerable potential
monary bronchi, visceral pleura, and hilar lymph nodes, both drain-
mobility in terms of ¬‚exion, extension, and rotational movements
ing into the pulmonary veins. The bronchial vessels, although small,
over the length of the twelve vertebrae. There is a progressive increase
are of great clinical importance. They maintain perfusion of the
in the height of thoracic vertebrae bodies from T1 to T12 and these
lung after a pulmonary embolism so that, if the patient recovers,
vertebrae can be distinguished by the presence of lateral facets, which
the affected lung returns to normal.
articulate with the heads of the ribs. Facet joints for articulation with
The thoracic duct the tubercles of the ribs are also present on the transverse processes
of T1 to T10. Furthermore, when viewed in the sagittal plane, each
The thoracic duct is the main channel by which lymph is returned to
the circulation. The thoracic duct begins within the abdomen as a
dilated sac known as the cistrna chyla and ascends through the
diaphragm on the right of the aorta. At the level of the sixth thoracic
vertebral body, the thoracic duct crosses to the left of the spine and
passes upwards to arch over the subclavian artery. The duct drains
lymph into a large central vein, which is close to the union of the left
internal jugular and subclavian veins. The diameter of the thoracic
Fig. 3.16. Targeted view
duct may vary between 2 and 8 mm and, although usually single, mul-
from a PA chest
tiple channels may exist. In normal subjects, the thoracic duct is col-
radiograph
lapsed and, as such, cannot be visualized on imaging studies. A
demonstrating a
variation on the normal is for a right-sided lymphatic duct, which unilateral left sided
drains lymph from the right side of the thorax, the right upper limb, calci¬ed cervical rib
and right head and neck into the right brachiocephalic vein. (arrows).


29
jonathan d. berry and sujal r. desai
The chest wall and ribs


vertebrae can be seen to possess a long spinous process; with the Fig. 3.17. Coronal
magnetic resonance
exception of T1 (whose spinous process is almost horizontal), the
image of the posterior
spinous processes all point downward.
aspect of the thorax at
Initial analysis of the thoracic vertebrae is still best done with a suit-
the level of the
ably penetrated plane ¬lm. However, in the presence of complex
* acromion process of the
trauma or where the contents of the spinal canal need to be visual- scapula (arrow) showing
ized, CT and MRI are being employed increasingly. the erector spinae
muscles (asterisk).
Muscles of the chest wall
There is a complex arrangement of muscles around the chest which,
in addition to the vital act of breating, help to maintain stability.
Outermost and anteriorly are the pectoralis (major and minor)
muscles; serratus anterior is situated laterally, and posterolaterally are
the muscles of the shoulder girdle. Posteriorly and adjacent to the ver-
tebrae are erector spinae and trapezius. These muscle groups are ganglia within the thorax. The ¬rst ganglia is frequently fused with
readily depicted on axial (CT and MRI) images (Fig. 3.17). The deeper the inferior cervical ganglia to form the cervicothoracic or “stellate”
muscles of the chest include the intercostal muscles (external, inter- ganglia. The remaining ganglia are simply numbered so that they cor-
nal, and innermost), which are situated between the ribs. Elsewhere, respond to the adjacent segmental structures. A number of plexi are
the subcostal muscles span several ribs and further muscles attach the formed through the fusion of different ganglia, for example, the
ribs to the sternum and vertebrae. All these muscles may be visualized cardiac plexus and aortic plexus.
accurately with MR.
Each intercostal space is supplied by a single large posterior inter-
The diaphragm
costal artery and paired anterior intercostal arteries. Incidentally, each
posterior intercostal artery also gives off a spinal branch, which sup- The diaphragm is the domed structure, which serves to separate the
plies the vertebrae and spinal cord. The venous drainage is via the contents of the thorax from those of the abdomen and plays a vital
posterior intercostal veins running backward to drain into the azygos role in breathing. The components of the diaphragm are a peripheral
(or hemi-azygos) and the anterior intercostal veins into the internal muscular portion and a central tendon. The diaphragm is ¬xed to the
thoracic and musculophrenic veins. chest wall at three main points: the vertebral attachment (via the
crura which extend down to the level of the lumbar vertebrae), the
Nerve supply of the chest wall costal component (comprising slips of muscle attached to the the deep
The innervation of the chest wall is via 12 paired thoracic nerves. part of the six lowermost ribs), and ¬nally the sternal component
The 11 pairs of intercostal nerves run between the ribs while the (consisting of slips of muscle arising from the posterior aspect of the
twelfth pair (the subcostal nerves) runs below the twelfth rib in xiphoid process). At three points, roughly in the midline, the central
the anterior abdominal wall. The intercostal nerves are the anterior tendon transmits (and is pierced) by the esophagus, descending aorta,
rami of the ¬rst 11 thoracic spinal nerves, which enter the inter- and inferior vena cava.
costal space between the parietal pleura and posterior intercostal The normal diapragm is easily visualized on both frontal and lateral
membrane to run in the subcostal groove of the corresponding radiographs as a smooth but curved structure. Laterally, on the frontal
ribs and below the intercostal artery and vein. It is for this reason radiograph, the diaphragm appears to make contact with the chest
that, whenever possible, needle aspiration or pleural drainage should wall. At the apparent point of contact (called the costophrenic recess)
be performed by entering the pleural space immediately above. the angle subtended to the chest wall is acute and well de¬ned. This
In addition to the peripheral nervous system, the sympathetic chain is of practical value since even small collections of ¬‚uid (pleural
is also found within the thorax. There are either 11 or 12 sympathetic effusions) will lead to a blunting of the costophrenic recess.




30
Section 2 The thorax

Chapter 4 The breast


STELLA COMITIS




Breast cancer is the commonest malignancy in women in Europe and underdevelopment of breast tissue is less common. The severity
the United States. In recent years, physicians and the media have ranges from amastia, the complete absence of glandular tissue, nipple
encouraged women to practice self-examination, to have regular evalua- and areola, to hypoplasia, the presence of rudimentary breasts.
tion by a medical practitioner, and to participate in breast screening
programs. This has resulted in the general population developing a
Breast anatomy
heightened awareness of breast cancer and in turn presenting to the
general practitioner with a variety of breast complaints. In order to The adult breast lies on the anterior chest wall between the second
evaluate properly such symptoms, there must be an understanding rib above and the sixth rib inferiorly, and from the sternal edge medi-
of the normal breast. This chapter serves to describe normal breast ally to the mid-axillary line laterally. Breast tissue also projects into
anatomy and the role of imaging techniques used to evaluate the the axilla as the axillary tail of Spence. The breasts lie on the pectoral
breast. fascia, covering the pectoralis major and minor muscles medially and
serratus anterior and external oblique muscles laterally. The breasts
are contained within a fascial sac, which forms when the super¬cial
Embryology
pectoral fascia splits into anterior (super¬cial) and posterior (deep)
During the fourth gestational week, paired ectodermal thickenings layers. The suspensory Cooper™s ligaments are projections of the
called mammary ridges (milk lines) develop along the ventral surface super¬cial fascia that run through the breast tissue and connect to
of the embryo from the base of the forelimb buds to the hindlimb subcutaneous tissues and skin.
buds. In the human, only the mammary ridges at the fourth inter- The nipple is found centrally on each breast and has abundant
costal space will proliferate and form the primary mammary bud, sensory nerve endings. The lactiferous ducts each open separately
which will branch further into the secondary buds, develop lumina on the nipple. Surrounding the nipple is the areola, which is pigmented
and coalesce to form lactiferous ducts. By term, there are 15“20 lobes and measures 15“60 mm. Near the periphery of the areola are eleva-
of glandular tissue, each with a lactiferous duct. The lactiferous ducts tions (tubercles of Morgagni) formed by the openings of modi¬ed seba-
open onto the areola, which develops from the ectodermal layer. The ceous glands, whose secretion protect the nipple during breastfeeding.
supporting ¬brous connective tissue, Cooper™s ligaments, and fat in The human breast contains 15“20 lobes. Each of these lobes has
the breast develop from surrounding mesoderm. a major duct, which connects to, and opens on, the nipple. Each lobe
At birth, the mammary glands are identical in males and females and consists of numerous lobules, which in turn are made of numerous
remain quiescent until puberty, when ductal growth occurs in females acini (or ductules). This forms the basis of the terminal ductal lobular
under the in¬‚uence of estrogens, growth hormones and prolactin. unit (TDLU), which is a histological descriptive term. The TDLU is an
When pregnancy occurs, the glands complete their differentiation by important structure, as it is postulated that most cancers arise in the
eventually forming secretory alveoli. After the menopause, decreased terminal duct, either inside or just proximal to the lobule. The ducts
hormone levels lead to a senescent phase with involution of the glandu- are named according to their position along the branching structure.
lar component and replacement with connective tissue and fat. The acini drain into the intralobular ducts which drain into the extralob-
Congenital breast malformations fall into two categories: the pres- ular ducts and eventually into the main duct, which opens on the
ence of supernumerary tissue, or the underdevelopment of breast nipple. The acini and ducts structures form the glandular breast
tissue. If the milk line fails to involute, it results in supernumerary parenchyma, which is surrounded by fatty tissue and ¬brous connec-
breast tissue. The commonest form, found in 2“5% of the population, tive tissue, which forms the stroma.
is polythelia, which is the presence of two or more nipples along the The glandular breast parenchyma predominates in the anterior
chest wall in the plane of the embryonic milk line. The absence or third and upper quadrant of the breast. Between the glandular

Applied Radiological Anatomy for Medical Students. Paul Butler, Adam Mitchell, and Harold Ellis (eds.) Published by Cambridge University Press. © P. Butler,
A. Mitchell, and H. Ellis 2007.

31
The breast stella comitis


Normal axillary lymph nodes can be demonstrated on both mam-
parenchyma and the pectoral muscle, there is predominantly fatty
mography and ultrasound. On mammography, nodes are oval struc-
tissue named the retroglandular tissue.
tures with a lucent centre due to the fatty hilum and should measure
The relative amounts of glandular breast tissue and stroma alter over
less than 2 cm. On ultrasound, normal nodes are oval with a hypoe-
the normal lifespan. Younger women have more glandular breast tissue
choic rim and a bright center (Figs. 4.1, 4.2). Arterial and venous
and, with increasing age, this is replaced with ¬brofatty tissue, particu-
supply is seen entering and leaving from the hilum, which can be
larly after the menopause. Women who take hormone replacement
notched with the result that the lymph node will have a bean-shape.
therapy preserve the glandular breast tissue for a longer period. With
pregnancy, the number of acini is increased and this persists in the lac-
tation period. After pregnancy, the acini decrease in number and the
Imaging
breast will be less dense than prior to pregnancy. There is, however,
great variation in the composition of breast tissue with some women Mammography allows excellent characterization of breast tissue.
having fatty breasts throughout their lives and others with extremely Special mammography units use low dose radiation to image the
dense glandular and ¬brous tissue. breast tissue. Mammography is most suitable for women over the age
of 40, as at a younger age the glandular tissue is very dense and differ-
entiation of the tissues is dif¬cult. Mammography can be performed
Arterial supply
with the patient seated or standing. To maximize the tissue imaged,
The arterial supply of the breast is derived from branches of the inter- the breast needs to be pulled away from the chest wall and com-
nal thoracic artery, lateral thoracic artery, and posterior intercostal pressed. Compression creates a uniform thickness through which the
arteries. Venous drainage is primarily into the axillary vein but also X-ray beam penetrates so that a uniform exposure can be obtained.
into the internal thoracic vein, subclavian vein, and azygos vein. Compression also reduces motion artifact by holding the breast still
and by separating overlapping structures.
Two views of each breast are obtained in the ¬rst instance: a medio-
Nerve supply
lateral-oblique (MLO) view and a cranio-caudal (CC) view. The MLO
Innervation of the breasts is primarily via the anterior and lateral view allows the breast to be viewed in pro¬le, ideally from high in the
cutaneous branches of the upper six thoracic intercostal nerves. axilla to the inframammary fold (Fig. 4.3). In the CC projection the
breast is viewed as if looking from above the breast downwards. In an
adequate CC projection, the nipple is seen in pro¬le and the retroglan-
Lymphatics
dular fat should be visible. Generally, more tissue can be projected on
Understanding the lymphatic drainage of the breast is vital because of
its importance in the spread of malignant disease. The majority (97%)
of the lymph from the breast drains to axillary nodes, and approxi-
mately 3% drains to the internal thoracic nodes. For surgical purposes,
to plan the removal of pathological nodes, the axilla is divided into
three arbitrary levels. Level I nodes (low axilla) lie lateral to the lateral
border of the pectoralis minor muscle, level II nodes (mid axilla) lie
behind the muscle, and the level III nodes (apical axilla) are located Bright fatty hilum
medial to the medial border of the pectoralis minor muscle.
The concept of a sentinel node, which is de¬ned as the ¬rst node that
drains a cancer, was ¬rst described in relation to melanoma and subse-
quently adapted to breast tumors. A blue dye (or more recently in
combination with a radiolabeled colloid), is injected into the tumor
and the identi¬cation of this dye in the sentinel node will predict the Fig. 4.2. Ultrasound of the axillary tail demonstrating a normal axillary lymph
status of the remaining nodes (95% accuracy). node with central fatty hilum.




Pectoralis major muscle

Normal axillary
lymph nodes
Glandular tissue
Retroglandular fat




Fatty tissue
Glandular tissue


Nipple in profile



Fig. 4.1. Mammogram in the mediolateral oblique (MLO) projection, Fig. 4.3. Mammogram in the mediolateral oblique (MLO) projection. The
demonstrates normal sized axillary lymph nodes with notched hilum. Note pectoralis major muscle projects to the level of the nipple and the retroareolar
the normal calci¬ed vessels bilaterally. fat is well seen. The nipple is visualized in pro¬le.


32
The breast stella comitis

(c)
the MLO projection than on the CC projection because of the slope
and curve of the chest wall. The pectoralis major muscle is visualized
in only 30“40% of women on a normal CC view (Fig. 4.4).


Normal mammographic patterns
Patterns of normal breast parenchyma vary greatly (Fig. 4.5). The most
widely accepted classi¬cation of breast patterns is that of Wolfe,
which consists of four groups.


Pattern type Description

N1 Predominantly fatty parenchyma
P1 15“25% nodular densities
P2 35% nodular densities
DY pattern Extreme nodularity and density




Calcified cyst




Retroglandular fat tissue
Glandular tissue




Pectoralis major muscle (d)




Fig. 4.4. Mammogram in the cranio-caudal (CC) projection. The retroglandular
tissue is seen but the pectoral muscle is only visible in 30“40% of CC projection
mammograms.

(a) (b)




Fig. 4.5. Wolfe
classi¬cation of breast
parenchymal patterns
(a) N1 predominantly
fatty tissue (b) P1 is less
than 25% nodular tissue
(c) P2 is greater than
25% nodular tissue
(d) DY pattern is
uniformly extremely
dense breast tissue.

33
The breast stella comitis


Viewing a mammogram Skin

As with all imaging, abnormalities on mammogram are seen as a dis-
ruption in the normal anatomical pattern. Mammograms should be
Fat lobule
viewed back-to-back as mirror images of each other. The breast
parenchyma should be symmetrical. Any areas of asymmetry, dif-
fering density between the breasts or architectural distortion, should
be viewed with suspicion. A magnifying glass should be used to assess
Pectoralis
areas of microcalci¬cation. major muscle



Rib
Ultrasound Chest cavity

Fig. 4.6. Ultrasound transverse image demonstrating normal breast parenchyma
Since the 1980s, high resolution probes perform “real-time” examina-
with lobules of fat interspersed with bright bands of ¬brous septa.
tion of breast tissue. Breast ultrasound is now seen as the most impor-
tant adjunct to assessing breast tissue. It is, however, not used alone
for routine screening for breast disease. The advantages of ultrasound
Fat lobule
in imaging the breast include reproducible size evaluation of lesions,
differentiation of solid from cystic structures and evaluation and
biopsy of abnormalities close to the chest wall and in the periphery Fibrous septa
Pectoralis major
of the breast.
muscle
The following tissue layers can be differentiated with ultrasound:
skin and nipple, subcutaneous fat, glandular tissue and surrounding
Rib casting
¬brous tissue, fat lobules, breast ducts, pectoralis major muscle, ribs posterior
shadow due to
and intercostal muscle layer. Deep to the ribs, the pleura is identi¬ed calcification
Pleura with
as a thin, very bright, echogenic layer (Figs. 4.6, 4.7, 4.8). Lymph nodes chest cavity
below
in the breast and axilla are identi¬able as oval structures with low
density periphery, a notched hilum, and an echogenic centre.
Fig. 4.7. Ultrasound axial image of axillary tail demonstrates normal breast tissue
and the underlying chest wall structures.
Magnetic resonance imaging (Fig. 4.9)
Although mammography has revolutionized imaging of the breasts,
there are still a number of instances where suboptimal imaging is
obtained with mammography. In some breasts, X-rays are severely
attenuated, which results in poor penetration and suboptimal visual-
ization of masses. These problems are seen in women with mammo- Prominent ducts
Leading to nipple
graphically dense breasts, in the presence of breast prostheses, and system
in scar tissue.
Magnetic resonance imaging is therefore most useful to assess
the integrity of breast implants and normal tissue around the
implants, to assess postoperative breast tissue as it allows differen-
tiation of tumour recurrence from scar tissue, and to look for
multifocal disease in dense breasts. While MRI is highly sensitive
for detection of focal lesions, its speci¬city for lesion characterization Fig. 4.8. Ultrasound of the retroareolar region demonstrating prominent breast
is not as high, and so it should not be used as a solitary ducts joining to form a single duct which opens on the nipple.
imaging modality, but rather as an adjunct to mammography
and ultrasound.
Nipple



Glandular tissue




Fat



Pectoralis major
muscle



Fig. 4.9. Axial MRI of the breast tissue demonstrates predominantly fatty breast
parenchyma with a little residual glandular tissue in the retroareolar regions.


34
The breast stella comitis


Further reading 6 Jackson, V. P., Hendrick, R. E., Feig, S. A., and Kopans, D. B. (1993). Imaging of the
1 Friederich, M. and Sickles, E. A. (2000). Radiological Diagnosis of Breast Diseases. radiographically dense breast. Radiology, 188, 297“301.
Berlin:Springer Verlag. 7 Wolfe, J. N. (1976). Breast parenchymal patterns and their changes with age.
2 Kopans, D. B. (1998). Breast Imaging. 2nd edn. Philadelphia: Lippincott-Raven. Radiology, 121, 545“552.
3 Gray, H. (1999). Gray™s Anatomy. Courage Books. 8 Tanis, P. J., Nieweg, O. E., Valdes, Olmos, R. A., Kroon, B. B. (2001). Anatomy and
4 Husband, J. E. S. and Reznek, R. H. (1998). Imaging in Oncology. Oxford: Isis Medical physiology of lymphatic drainage of the breast from the perspective of sentinel
Media. node biopsy, J. Am. Coll. Surg. 193(4), 462“465.
5 Harris, J. R., Lippman, M. E., Morrow, M., and Osborne, C. K. (2000). Diseases of the 9 Tabar, L. and Dean, P. B. (2001). Teaching Atlas of Mammography. Thième Medical
Breast. 2nd edn. Philadelphia: Lippincott, Williams & Wilkins. Publishers.




35
Section 3 The abdomen and pelvis

Chapter 5 The abdomen


DOMINIC BLUNT




The anterior abdominal wall comprises a number of layers. From
super¬cial to deep these are: the skin and super¬cial fascia layers, sub-
cutaneous fat, muscles and their aponeuroses, extraperitoneal fat, and
the peritoneum itself. These layers extend from the xiphoid, lower
costal cartilages and ribs to the bones of the pelvic brim inferiorly.
The lower ribs and chest wall overlie many structures in the upper
abdominal cavity.
The super¬cial fascia is subdivided into layers and contains predom-
inantly fat, with lymphatics, nerves, and vessels. The fat within it is
the most conspicuous component on imaging and the thin fascial
layers are continuous with layers of super¬cial fascia over the thighs
and external genitalia inferiorly, and the chest wall superiorly.
The muscles comprise three sheet-like layers (the external oblique,
the internal oblique and the transversalis muscles). These become thin
aponeuroses medially. Medially are the paired band-like rectus abdo-
minis muscles. Fat and connective tissue can be seen between these
layers on imaging (Fig. 5.1). Transversalis Internal External
muscle oblique oblique muscle
The super¬cial muscle layer is the external oblique and its aponeu- muscle
rosis. This originates from the outer aspects of the lower ribs and the
Fig. 5.1. Axial CT image at the level of the lower pole of the kidneys. Note the
muscular slips unite to run inferomedially, continuing as an aponeu-
rectus abdominis muscles joined in the midline, and laterally the three layers
rosis inserting in the midline into the linea alba (a tough band of con-
(external oblique, internal oblique and thin transversalis), whose fascia can be
nective tissue) where it joins the aponeuroses of the other two seen passing deep to the rectus muscle.
sheet-like muscles. Inferiorly, it inserts into the anterior half of the
iliac crest and the pubic tubercle, the inferior part of the aponeurosis
forming the inguinal ligament, stretching from the anterior superior The inguinal canal runs between layers of the aponeuroses in the
iliac spine to the pubic tubercle. line of the inguinal ligament and marks the line of descent of the
The internal oblique originates from the inguinal ligament, the iliac testis in the male. The sites where this enters and exits the canal com-
crest, and thoracolumbar fascia. It runs in a broad fan superomedially prise de¬ciencies in the abdominal wall through which a hernia may
and its aponeurosis inserts into the lower ribs, the linea alba, and protrude.
pubis. The rectus abdominis muscles originate from the pubic bone inferi-
The third layer is the transversus abdominis, which runs trans- orly and insert into the xiphoid and medial costal cartilages.
versely from the internal aspect of the lower ribs, the thoracolumbar Deep to these muscles and aponeuroses lies extraperitoneal fat and
fascia, the iliac crest, and inguinal ligament. Its aponeurosis inserts the peritoneum itself.
into the linea alba and inferiorly into the pubic tubercle. The layers are well seen with ultrasound, CT and MRI but are
Medially, the common aponeurosis of these three muscles forms the seldom imaged speci¬cally other than in relation to intra-abdominal
rectus sheath, which in the upper abdomen forms layers anterior and or pelvic pathology. Clinically, they are clearly important in abdomi-
posterior to the rectus muscle; in the lower abdomen the sheath runs nal and pelvic surgical practice, when the method for dividing them
only anterior to it. and repairing them is dictated by the access needed and the anatomy.

Applied Radiological Anatomy for Medical Students. Paul Butler, Adam Mitchell, and Harold Ellis (eds.) Published by Cambridge University Press. © P. Butler,
A. Mitchell, and H. Ellis 2007.

36
The abdomen dominic blunt


The gastrointestinal tract
The gastrointestinal tract is a long tubular structure extending from
the pharynx to the anal canal. There are many ways in which this can
be imaged. Gas within bowel is visible on plain radiographs, while
examinations using a suspension of barium sulfate to coat or ¬ll the Indentation
from aortic arch
lumen demonstrate the anatomy and details of the bowel wall. CT and
MRI can be used to study the cross-sectional anatomy and the sur-
rounding anatomical structures. Less commonly, nuclear medicine
Indentation
techniques investigate functional anatomy, and, particularly in the from left main
bronchus
infant, ultrasound has a role in studying the gut. Endoluminal ultra-
sound shows detailed wall structure and is used particularly in the
assessment of tumors.


Esophagus Indentation
from left atrium
The esophagus is a muscular tube, around 23 cm long in the adult,
extending from the level of C6 where it begins below the pharynx,
to the gastro-esophageal junction at around T10. The majority of its
course is within the thorax.
At its origin it is a ¬‚attened tube lying slightly to the left of the
midline behind the trachea, with the prevertebral muscles posteriorly.
Fig. 5.2. Barium swallow image taken in an oblique projection. The esophagus is
Anterolaterally are the thyroid lobes and carotid arteries, and internal outlined by barium and distended with air. Note shallow indentations form the
jugular veins, as well as the vagus nerves. The recurrent laryngeal arch of the aorta, the left main bronchus and, inferiorly, the left atrium.
nerves lie between it and the trachea.
Throughout the thoracic course of the esophagus, the vertebral
column forms the major posterior relation, with the azygos and hemi-
azygos venous systems to the right and left posteriorly and the thoracic
duct between it and the azygos vein. The pleura lies close to it laterally
on the right, other than where the azygos vein arches anteriorly to join
the superior vena cava. On the left, the left subclavian artery and tho-
racic duct pass between it and the pleura in the superior mediastinum,
and below this the aortic arch and descending thoracic aorta make up Left
main
its main relations. From superior to inferior its anterior relations are bronchus
Eesophagus
the trachea, left main bronchus, and lymph nodes. Below this lie the
Aorta
pericardium and the left atrium and inferiorly the diaphragm.
It enters the abdomen between the left crus of the diaphragm and
Azygos
the left lobe of the liver and passes to the left of the midline towards vein
the gastro-esophageal junction.
The blood supply of the esophagus derives from the inferior thyroid
arteries in the neck, via small branches directly from the aorta in the
Fig. 5.3. CT image to demonstrate the relations of the oesophagus in the
thorax and from the celiac artery via the left gastric in its lower third. mediastinum. Note the left main bronchus anteriorly and the aorta and azygous
Its lymphatic drainage is to local nodes along its length, which drain vein posteriorly. The pleura and lungs are the lateral relations.
superiorly into the deep cervical nodes and inferiorly towards the
celiac axis group.
technique is almost exclusively used in the assessment of esophageal
The muscular wall is skeletal muscle in the upper third with transi-
tumors and their local spread.
tion into smooth muscle in the lower third.
When distended with barium, the anterior wall of the oesophagus is
indented by the arch of the aorta and inferiorly the left main
Stomach
bronchus. In the lower thorax the left atrium makes a long shallow
The stomach is a wide muscular bag and represents the widest part
anterior indentation in it (Fig. 5.2). Using barium and gas distension
of the gut. It has a variable shape and lie depending on the build of
(“double contrast”) the mucosa of the esophagus is demonstrated, and
the subject. As well as having a roughly “J” shape in the erect position,
liquid and solid swallows allow dynamic assessment of motility.
its proximal part lies posteriorly, with the distal stomach curving
Motility is frequently studied with video series in the upper esophagus
anteriorly as it passes downwards and to the right. In the empty state
with the patient erect, whereas the lower esophagus is best assessed
it is ¬‚attened antero-posteriorly. The inferior edge is referred to as
with the patient prone. CT and MRI allow visualization of the wall of
the greater curve, and the superior edge is the lesser curve. Inferiorly
the esophagus and the surrounding structures (Fig. 5.3). Endoscopic
on the lesser curve is a variably de¬ned notch called the incisura
ultrasound gives very detailed information of the esophageal wall as
angularis.
well as of surrounding structures particularly local lymph nodes. This

37
The abdomen dominic blunt


The stomach is divided into a number of areas for the purposes of
description, although these anatomical divisions are not strictly
de¬ned by changes in structure or function.
Proximally, the gastro-esophageal junction opens at the cardia into
the fundus. This is the superior part and lies beneath the left hemidi-
aphragm. It also represents the most posterior part of the stomach. Gastric
fundus
The body of the stomach extends from the fundus to the incisura
where it then becomes the antrum. The pylorus or pyloric canal
represents the outlet of the stomach into the duodenum and lies to
the right of the midline at a variable level depending on gastric ¬lling
and position of the subject. First part
of the
The wall of the stomach contains layered smooth muscle, while duodenum
the mucosal surface contains large longitudinal mucosal folds called
rugae. These become less prominent when the stomach is distended. Lesser
curve
The anatomical relations of the stomach are anteriorly, the left of stomach
lobe of the liver above and the abdominal wall inferiorly. Posterior to
the stomach is a blind ended peritoneal recess called the lesser sac
(see section on peritoneal anatomy) which lies between it and its
posterior relations. These are the ¬bers of the left hemidiapragm
arching upwards towards the dome of the diaphragm, the spleen,
and splenic artery, the left adrenal and upper pole of the left kidney
and, inferiorly the body and tail of pancreas overlaid by the transverse
Fig. 5.4. Stomach on barium meal, in supine position. The stomach mucosa is
mesocolon.
coated with barium and distended with air. The posteriorly-lying fundus
The stomach is invested in peritoneum. This is in contact above the contains dense barium. The ¬rst part of the duodenum is distended with air,
stomach to form the lesser omentum and, inferiorly, meets further while the descending second part contains barium.
folds of peritoneum from around the transverse colon to form the
greater omentum, which often contains prominent fatty tissue and
spreads inferiorly as an apron-like fold and is the ¬rst structure seen
on opening the peritoneum anteriorly.
The blood supply is from branches of the celiac artery. The major
Left lobe
branches run along the greater and lesser curves, small branches radi- of liver
ating from these over the anterior and posterior surface of the
stomach.
The lymphatics correspond to the arterial branches, most draining
to celiac axis groups.
The modalities used to image the stomach are as for the esophagus.
Gas frequently makes the fundus particularly visible on the erect
chest radiograph, while the body is often seen on the supine abdomi-
Gastric Spleen
nal image. Double contrast barium techniques show the rugae and rugae
mucosa (Fig. 5.4), although the barium meal examination has been
Fig. 5.5. Axial CT image through the upper abdomen. The gastric rugae are well
superseded in much clinical practice by endoscopy. In the infant, the
demonstrated (compare with the barium meal image). Note the position of the
pylorus may be evaluated by ultrasound in the diagnosis of infantile
stomach, passing anteriorly below the left lobe of the liver, and on the
hypertrophic pyloric stenosis. Gastric emptying can be evaluated in
anteromedial side of the spleen. Fat lying between these structures appears
a quantitative functional manner with isotope studies. CT is used in black on CT.
the evaluation of gastric malignancies, and the stomach™s relations are
well demonstrated on this and MRI (Fig. 5.5).
relations. Posteriorly are the portal vein and bile duct, and the inferior
vena cava. The gastroduodenal branch of the hepatic artery also lies
Duodenum
posterior to it. On its inferior surface lies the pancreatic head.
The second part runs in a vertical orientation. On its medial surface
The duodenum is a roughly C-shaped tube, which runs from the
lies the head of the pancreas and it is into it that the common bile
pyloric canal to the jejunum. For most of its curved course it has
duct and pancreatic duct open, usually together at the ampulla of
the pancreas on its inner margin. For descriptive purposes it is
Vater, but with common anatomical variations. Posteriorly lie the
divided into four parts, although there is no structural change
right renal vessels, renal pelvis, and part of the kidney itself.
between each part.
Anteriorly and laterally lie parts of the colon (the hepatic ¬‚exure and
The ¬rst part of the duodenum passes posterosuperiorly from the
proximal transverse colon) and part of the right lobe of the liver.
pylorus. It is partly within the peritoneum but distally becomes

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