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ANATOMY FOR DIAGNOSTIC IMAGING
Blood supply of the bladder The bladder is supplied via the internal iliac artery via superior and inferior vesical arteries. Venous drainage is via a venous plexus to the internal iliac vein. Lymph drainage This is along the blood vessels to internal iliac and thence to para-aortic nodes. Applied anatomy Bladder rupture may occur with fractures of the pelvis owing to the rigid fixture of the bladder neck to the pelvis. Such ruptures are usually extraperitoneal; extravasated urine may track into the scrotum and the anterior abdominal wall. Intraperitoneal rupture may occur in blunt trauma to the abdomen when the bladder is full. The point of tear is usually at the junction of the loose and the fixed peritoneum at the posterior part of the bladder. Radiology of the bladder Plain films The bladder may be identified on plain films, especially when full. It is seen as a round soft-tissue density surrounded by a lucent line of perivesical fat. It should be smooth and symmetrical. The median umbilical ligament is a fibrous remnant of the urachus, which runs from the apex of the bladder to the umbilicus in the fetus. This may be seen outlined by air in pneumoperitoneum. Contrast studies The bladder may be filled with contrast either after intravenous injection in intravenous urography or retrogradely via the urethra. The corrugations of the bladder wall are seen. The smooth impression of the uterus may be seen posterosuperiorly. The prostatic impression is seen inferiorly in the male. Irregular collections of contrast may be trapped between muscle fibres after micturition. Cross-sectional imaging (see Figs 6.4 and 6.5) The bladder is readily identified by ultrasound, CT and MRI, especially when distended. Ultrasound is best for assessing its internal anatomy. CT and MRI have the advantage of also being able to assess the surrounding structures. THE MALE URETHRA (Fig. 6.13) The male urethra runs from the internal urethral sphincter at the neck of the bladder to the external urethral orifice at the tip of the penis. In radiological terms it may be divided
into posterior and anterior parts. The posterior urethra comprises the prostatic and membranous urethra and the anterior part comprises the bulbous and penile urethra. The prostatic urethra traverses the ventral part of the prostate and is the widest part. It is about 3 cm long. It has a longitudinal midline ridge known as the prostatic crest. Several prostatic ducts open into the prostatic sinus, a shallow longitudinal depression on either side of the prostatic crest. The prostatic crest bears a prominence called the verumontanum (also known as the seminal colliculus). A small blindly ending sinus - the prostatic utricle - opens on to this. (This is the vestigial remnant of the uterovaginal canal in the embryo). On either side of, or just within, the prostatic utricle the ejaculatory ducts open. These are the common termination of the seminal vesicles and the vasa. The lower part of the prostatic urethra is relatively immobile as the prostate is fixed here by the puboprostatic ligaments. The membranous urethra is so called as it traverses the membranous urogenital diaphragm, which forms the (voluntary) external urethral sphincter. It is the narrowest part of the urethra and is about 2 cm long. The urethra is quite immobile at this point. A gland is present at either side at this point - Cowper's gland. The bulbous urethra lies in the bulb of the penis. It has a localized dilatation called the intrabulbar fossa. It is surrounded by the corpus spongiosum. The penile urethra is long and narrow, except for a localized dilatation at its termination - the navicular fossa. It is surrounded by the corpus spongiosum of the penis (see section on the penis). Applied anatomy Proximal urethral injuries are common with pelvic fractures owing to the fixed attachment of the distal prostatic and membranous urethra to the pelvic bones. Radiology of the male urethra (Fig. 6.13) In retrograde urethrography, the male urethra may be outlined by contrast, which is usually introduced retrogradely via a soft catheter in the navicular fossa. The intrabulbar fossa is seen and the various parts of the urethra are recognized by position and calibre. The verumontanum appears as a posterior filling defect in the prostatic urethra, and the utricle may fill. In voiding cystourethrography contrast in the bladder is voided, outlining the urethra from above. The technique allows better distension of the posterior urethra, which may be difficult to achieve with the retrograde approach. Penile sonourethrography may be performed with retrograde instillation of saline into the urethra, or during voiding where the distal urethra is clamped with a device or manually. This technique has the advantage of allowing evaluation of all of the structures of the penis.
