The adrenal glands

The intravesical portion of the ureter has an oblique course of 2 cm through the bladder wall. The vesical muscle has a sphincteric action and the obliquity has a valve-like action. The ureter opens into the bladder at the ureterovesical orifice.

Blood supply of the ureter

The ureter is supplied by branches of nearby arteries and drains to corresponding veins, that is, the aorta and IVC and the renal, gonadal, internal iliac and inferior vesical vessels. Despite the varied arterial supply, the ureter is prone to vascular injury at surgery, which may lead to stricture formation.

The development of the ureter

The ureter develops as a blind diverticulum from the metanephric duct and grows first posteriorly and then cranially to unite w i th the developing kidney.

Developmental abnormalities and variants Duplication of part or all of the ureter occurs in about 4% of subjects. It is the commonest significant congenital anomaly of the urinary tract. Duplication is two to three times commoner in females. When complete duplication occurs, the ureter serving the upper renal moiety drains fewer calyces and is inserted lower into the bladder than that draining the lower moiety - known as the Weigert-Meyer law. The low insertion may extend to the bladder neck or the urethra or, in females, the vestibule or vagina.

Ureteric ectopy is most common in association w i th duplication, but may occur alone.

Ureterocoele is a dilation of the intramural portion of the ureter due to narrowing of its orifice. This is most common in a duplicated system, when it occurs in the ureter draining the upper renal moiety that is usually ectopic.

Radiological features of the ureter

Plain films of the abdomen

The ureter is not visible, but a knowledge of its course in relation to the skeleton is necessary when looking for radio-opaque calculi. The ureters pass anterior to the tips of the transverse processes of L2-L5 lumbar vertebrae and anterior to the sacroiliac joint. They then curve laterally at the ischial spines and medially again to the bladder.

Intravenous urography (see Fig. 5.49) The ureters are either completely or partly visible when filled w i th contrast. Their course is as above. The ureter passes anteriorly from the kidney to its position near the psoas muscle. Prone views aid ureteric filling. Distension of the upper part of the collecting system can also be aided by applying a compression band across the abdomen during the first part of the IVU examination. The ureter enters the posterior part of the bladder, and oblique views are therefore helpful in imaging the ureterovesical junction.

Varying degrees of ureteric duplication may be seen w i th the ureters uniting at any point of their course. Other variants already discussed may also be identified.

Ultrasound The proximal and distal ureters may be visible on ultrasound when well distended. Intestinal gas generally obscures the midportion unless it is abnormally dilated.

Computed tomography Ureteric calculi not visible on radiographs are readily visible on CT scans, and non-contrast CT has largely replaced the IVU for diagnosis of ureteric calculi. The normal ureter can be identified on non-contrast scans, although it is easier to identify if it contains contrast medium (see Fig. 5.4). It is visible medial to the lower pole of the kidney, anterior to psoas. More distally the ureter remains anterior to the psoas muscle and is lateral to the great vessels. Having crossed the bifurcation of the common iliac artery, the ureter in the pelvis is medial to the iliac arteries and veins. It enters the bladder posterolaterally. Variants such as duplication are easily identified.

MR urography The ureters may be imaged using the same water-sensitive techniques as MR cholangiography (see above). However, because they are intermittently collapsed due to peristalsis parts of the ureter may not be distended w i th urine and thus not imaged using these techniques. MR urography works well in a distended system. MR contrast urography can be performed where the ureters are imaged during the excretory phase after intravenous gadolinium. MRI tends to be used in cases where irradiation is undesirable, such as during pregnancy.

THE ADRENAL GLANDS (see Fig. 5.11) The adrenal glands lie retroperitoneally above each kidney. They are each enclosed w i t h in the perirenal fascia but in a separate compartment from the kidney. Each gland is composed of a body and medial and lateral limbs. The adrenal glands have an outer cortex derived from mesoderm and an inner medulla (10% of the weight of the gland), which is derived from the neural crest and is related to the sympathetic nervous system.

The right adrenal gland tends to have a consistent location. It lies posterior to the inferior vena cava, medial to the

right lobe of the liver and lateral to the right diaphragmatic crus. It is lower and more medial in relation to the spine than the left. On cross-section it is linear or V-shaped, w i th a larger medial limb and a smaller lateral limb.

The left adrenal gland lies posterior to the splenic vein and lateral to the diaphragmatic crus, but its position is less consistent than that of the right side. The left adrenal gland is more semilunar than the right and it extends down the superomedial border of the kidney towards the hilum. On cross-section it is triangular or Y-shaped.

Embryologically, the adrenals do not develop w i th the kidneys. They develop in the retroperitoneum and descend, whereas the kidneys develop in the pelvis and ascend (see above). In cases where the kidneys fail to ascend normally, the adrenal glands are still found in the expected position although their shape may be more discoid owing to lack of moulding by the kidneys during development.

At birth the adrenal glands are relatively much larger than in the adult - one third the size of the kidney at birth and one-thirtieth in the adult. The size of the gland is somewhat variable, but as a rule of thumb on cross-sectional imaging the limbs of the adrenal should not be thicker than the diameter of the adjacent crus of the diaphragm.

Arterial supply

Three arteries supply these glands on each side, namely: • The superior adrenal artery from the inferior phrenic artery; • The middle adrenal artery from the aorta; and • The inferior adrenal artery from the renal artery.

Venous drainage

One vein drains the adrenal gland on each side. The right adrenal vein drains to the IVC and the left adrenal vein drains to the left renal vein.

Variants

Small masses of adrenal cortical tissue called cortical bodies are often found near the adrenal glands. These may become attached to other organs early in embryology and migrate w i th these organs to be found in such places as the broad ligament of the uterus, the spermatic cord and even the epididymis.

Radiological features of the adrenal glands

Plain films of the abdomen

The adrenal glands are visible only if calcified, and they are then seen to be lateral to the spine at the level of the upper pole of the kidneys. Computed tomography (see Figs 5.11, 5.56 and 5.57) With modern scanners the adrenal glands can be identified in almost all subjects. The shape of the adrenal gland on CT cuts is variable, w i th a linear, inverted V shape being commonest on the right and a triangular or Y shape commonest on the left. Its craniocaudal extent is less than 4 cm and limb thickness is usually less than 1 cm.

The right adrenal gland is seen posterior to the IVC. More laterally it lies between the liver and the crura of the diaphragm. The left adrenal is higher and extends more laterally anterior to the kidney, from which it is separated by perirenal fat. Contrast medium may help to distinguish it from the adjacent splenic vessels.

Magnetic resonance imaging The adrenals are very well seen on MRI because of surrounding fat (more easily than w i th CT). They are iso- or slightly hypointense compared to liver on both T1- and T2-weighted images. They lose signal on fat suppression or fat subtraction techniques, depending on the cholesterol content of the adrenal cortex (Cortisol is derived from cholesterol esters).

Ultrasound

In thin individuals the adrenal glands can sometimes be seen between the kidney and liver on the right and between the kidney and pancreatic tail on the left using highresolution scanning. They are readily seen in neonates and usually seen in children.

Adrenal venography This may be performed for venous sampling in addition to imaging the veins. The right adrenal vein enters the IVC 3 cm above the renal vein near the neck of the twelfth rib, close to the entry of the hepatic veins. The left adrenal vein is easier to cannulate than the right. It enters the left renal vein near the lateral border of the vertebral body and receives the inferior phrenic vein.

Arteriography of the adrenal gland A ll three supplying arteries must be visualized on each side to be studied, as follows: • The superior adrenal artery usually consists of several branches from the inferior phrenic artery. It may arise separately from the aorta, usually above the coeliac artery, but may arise below this or from the renal artery. • The middle adrenal artery arises from the aorta and is multiple in more than 30% of studies. • The inferior adrenal artery may arise from the renal artery directly or w i th the superior capsular artery.

Other arteries to the adrenal gland may arise from the gonadal arteries.