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Urogenital Imaging

Diverticulum, urethral

It is thought that congenital urethral diverticula occur only in males, and that urethral diverticula in females are an acquired condition. In males, the diverticulum is typically found ventral to the urethra, with a narrow proximal neck. It may arise from defective closure of the urethral folds, or as a rudimentary form of urethral duplication. During voiding, the diverticulum fills from above, and may result in urethral obstruction (see anterior urethral valves) and urinary tract infection. The anomaly is usually well demonstrated on voiding cystourethrography. Urethral diverticula are common in adult females, occurring in as many 16% of all women. They typically arise from the posterior wall of the urethra, bulging into the vagina or vaginal introitus. Occasionally, they arise laterally or anteriorly. The origin is unknown. Most are probably acquired, though some can be congenital. Possible disguised causes include infection and obstruction of periurethral glands, and trauma from childbirth or repeated catheterization. Symptoms are often nonspecific, consisting of urgency, frequency, dysuria, dyspareunia, recurrent urinary tract infection, dribbling, and incontinence. Careful examination may demonstrate a palpable tender suburethral mass. Occasionally pus may be expressed from such a mass, or it may contain a palpable stone, or even a hard nodule due to complicating carcinoma. Urethral diverticula in women may be difficult to visualize radiographically. They may be visible on a voiding cystourethrogram, but only if they fill and distend with contrast. If the diagnosis is strongly suspected clinically, then special techniques to generate high pressure in the urethra should be used to force contrast into the diverticulum. This can be achieved by occluding the meatal opening with a finger during voiding, or by using a special double-balloon catheter technique that essentially seals the urethra at both ends and forces contrast into the diverticulum from a hole in the catheter between the balloons (Fig.1). Transvaginal sonography (Fig.2) and MRI have also been used to image urethral diverticula in women, particularly when standard imaging has failed to demonstrate a suspected diverticulum. Contrast-enhanced CT can also reveal urethral diverticulae (Fig.3).

Urethral diverticula have a characteristic MRI appearance. On T1-weighted images, the urethra is usually of homogeneous medium signal intensity. Occasionally, an area of lower signal intensity can be seen. On T2-weighted images, the fluid content within the submucosal region of a urethral diverticulum demonstrates high signal intensity (Fig.4). The outer low-signal-intensity wall is usually intact, although it may be thinned. Craniocaudal extension of the diverticulum can be appreciated on sagittal plane images. Following gadolinium-DTPA administration, the submucosal region is enhanced, but the area of diverticulum is not, permitting confirmation of the diagnosis of urethral diverticulum. As MRI becomes more widely available, its use in the study of urethral diverticula will probably expand even further.

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Fig.1

Double bubble urethrogram demonstrating a urethral diverticulum (arrow).
Diverticulum, urethral, Fig.1
Diverticulum, urethral, Fig.2
Diverticulum, urethral, Fig.3
Diverticulum, urethral, Fig.4