Median Raphe Cyst
Median raphe cysts are uncommon benign cysts that form in the midline region of the perineum. They most commonly occur on the ventral shaft of the penis but can occur anywhere from the urethral opening along the ventral surface of the penis, in the midline across the scrotum, and to the anus. This cyst is considered to be formed from a congenital abnormality of the genitalia. An abnormal folding of the urethral folds is believed to be the cause of these developmental cysts.
Clinical Findings: Most median raphe cysts are found in young boys on the ventral surface of the penis and midline scrotum. They have no race predilection. They are present at birth but may go unnoticed for some time, even into adulthood. They appear as small (0.5-1 cm), solitary, soft, translucent cystic nodules. They are almost always asymptomatic. On occasion, they can rupture and drain serous fluid. The cyst rarely connects to the underlying urethra or other structures. The clinical differential diagnosis can be very broad, and the only way to make a definitive diagnosis is to perform a biopsy or complete excision.
Pathogenesis: These cysts are believed to be caused by an abnormal folding or fusing of the paired urogenital/urethral folds during embryological devel- opment. These folds normally combine and fuse to form the external genitalia at about the eighth to tenth weeks of gestation. In the male the folds form the shaft of the penis, and in females they form the labia minora. Hypospadias is another congenital abnormality caused by improper folding of these embryological tissues. The ause of the abnormal folding has yet to be determined.
Histology: The cysts are lined with a pseudostratified or stratified columnar epithelium. The epithelium can closely approximate the appearance of transitional urethral cell epithelium. The lining surrounds a central cavity filled with serous fluid. Large mucinous cells are scattered throughout the columnar epithelium. The luminal cells have been shown to stain with cytokeratin 7, cytokeratin 13, epithelial membrane antigen (EMA), and carcinoembryonic antigen (CEA). Histologically, these cysts have a very characteristic appearance. The main pathological differential diagnosis is between the median raphe cyst and an apocrine cystadenoma. Immunohisto chemical staining can be used to differentiate the two.
Treatment: Simple surgical excision is all that is required for cure. They will not recur, because they are developmental cysts. Care should be taken not to damage underlying structures, and often a urological surgeon performs the procedure.