Urethral Diverticulum (Anterior)
A.  Anterior urethral diverticulum
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Congenital urethral diverticulum, though uncommon, is a known cause of urethral obstruction in boys and most commonly occurs in the distal and ventral urethra. Described as saccular or diffuse, the saccular type is a localized protrusion from the urethral lumen into the ventral wall of the anterior urethra, and the diffuse type is a generalized dilatation of the entire anterior urethra (synonymous with megalourethra or urethral ectasia). The diffuse type is associated with prune-belly syndrome. The congenital saccular diverticulum may produce anterior urethral obstruction by a valve-like mechanism of the distal lip of the diverticulum that obscures the urethral lumen during filling. In fact, the urologic literature describes the entity of an anterior urethral valve (please see separate discussion of this entity) as actually a congenital urethral diverticulum. The cause of congenital anterior urethral diverticulum is unknown. Hypotheses include in utero distal urethral obstruction, dilatation of the periurethral glands, and an incomplete urethral groove with faulty development of the corpus spongiosum of the penis. Like the anterior urethral valve, patients may present with penis swelling noted during micturation, caused by dilatation of the saccule and/or obstructive dilatation of the urethra. Intermittent obstruction of the urinary stream and simultaneous swelling of the penis strongly suggest an anterior urethral diverticulum. The diagnosis of this entity is confirmed with voiding cystourethrography. Difficulty with catheterization can be encountered because the catheter preferentially slips into the diverticulum. Because the diverticulum is almost always located within the ventral midline, and dorsally oriented coude-tipped catheter can usually be negotiated into the more proximal urethral. The entire penile urethra must be included in the voiding phase of the study, or more distal located lesions will be missed. The diverticulum usually involves the midportion of the penile urethra, though occasionally involves the bulbous urethra. The urethrographic appearance of a saccular diverticulum is characteristic. Contrast fills an oval ventral outpouching of the anterior urethra. Voiding cystourethrography is followed by renal sonography or scintigraphy to assess the anatomy and function of the upper urinary tract. Clinical management differs slightly from that of anterior urethral valves. A true anterior urethral valve (an obstructing membrane) may be treated by transurethral resection, whereas an anterior urethral diverticulum usually requires diverticulectomy and urethroplasty. The primary differential diagnostic considerations are anterior urethral valve and dilatation of a Cowper gland duct. Saccular dilatation of the distal ventral urethra is also commonly seen after hypospadias repair. Reference: Campbell’s Urology, 8th ed, pp 2225-2226. Practical Pediatric Imaging; Diagnostic Radiology of Infants and Children, 3rd ed, pp1059.