Cowper’s Duct Cyst
Cowper’s duct cyst or syringocele consists of cystic dilatation of Cowper’s gland ducts. The bulbourethral glands (Cowper glands) are paired paraurethral glands located in the urogenital diaphragm near the bulbous urethra. Their secretions, which have lubricating and spermatozoa-protecting functions, pass through paired Cowper ducts that enter the ventral surface of the proximal bulbous urethra.  Occasionally, reflux into Cowper’s ducts is observed during urethrography. A retention cyst, or syringocele, can occur with obstruction of the duct and gland, causing variable appearances of Cowper’s ducts and at their insertion into the bulbous urethra.

Though of uncertain embryologic origin, these lesions are likely congenital, as they are commonly observed in young patients with no clinical history. They are usually small, inconsequential lesions, but rarely can be of significant enough size to cause varying degrees of urethral obstruction. Four morphologic types have been described, that differ in their radiographic appearance: the simple syringocele presents as modest dilation of the bulbourethral (Cowper’s) duct; the imperforate syringocele, that does not communicate with the urethra and that causes submucosal cystic dilatation which at urethrography appears as a posterior urethral impression and/or filling defect at the level of Cowper’s ducts insertion; perforate syringocele, in which dilated excretory ducts communicate with the bulbar urethra, allowing reflux and opacification of Cowper’s ducts; and ruptured syringocele, which presents as thin, frail membranes persisting in the bulbous urethra after syringocele rupture.

Dilatation of Cowper’s Duct and syringocele are best shown on VCUG, as they maybe effaced by urethral distention that occurs during retrograde urethrography. Simple reflux into Cowper’s ducts can be caused by a patulous orifice, rupture of a retention cyst due to urethral instrumentation, spontaneous rupture of a retention cyst, or distal urethral obstruction. Adjunct diagnosis of syringocele has been described utilizing sonourethrography using a transperineal scanning, which shows a thin septation in the bulbar urethra dividing the distended lumen into two parts. Differential diagnosis for similar appearing lesions within the bulbar urethra includes a urethral diverticulum, partial duplication, ectopic ureter, fistula, blood vessel, or Muellerian duct remnant. Though uncommon, if a Cowper’s duct cyt/syringocele is implicated in outlet obstruction, management usually consists of endoscopic unroofing. After unroofing, a diverticulum-like defect may be present on the posterolateral wall of the bulbous urethra.

Campbell’s Urology, 8th ed, pp 2227.

Practical Pediatric Imaging; Diagnostic Radiology of  Infants and Children, 3rd ed, pp 1086.

Pavlica P, Barozzi L, Menchi I (2003) Imaging of male urethra. Eur Radiol 13:1583-1596
A. Imperforate syringocele (Cowper’s duct cyst)
B. Posterior urethra
C. Anterior urethra
A
B
C
Alternate Example
A. Imperforate syringocele (Cowper’s duct cyst)
B. Posterior urethra
C. Anterior urethra
D. Cobb’s collar
A
B
C
D
Differential Diagnosis
(Click on the image to go to a specific discussion)
Anterior valve
Urethral diverticulum
Urethral polyp