Median Raphe Cyst–Clinical Report and Immunohistochemical Analysis

Cysts of the median raphe are very rare. We describe a 20-year-old man with an asymptomatic nodule on the ventral surface of the penis. The nodule was surgically removed under local anesthesia, and send to histological and immunohistochemical analysis. Immunohistologicaly epithelial cells appeared Cytokeratin-7 (CK7), epithelial membrane antigen (EMA) positive and anti-S100 protein (S100), Cytokeratin-20 (CK20), smooth muscle actin (SMA) and carcinoembryonic antigen (CEA) negative. Histological and immunohystochemical findings indicate median raphe cyst.


Introduction
Median raphe cysts of the penis are benign lesions in young men [1,2]. Median raphe cyst was first described in detail by Mer met in 1895 [1,2]. These cysts are midline-developmental and can occur anywhere from the anus to the urinary meatus [1,2]. When located on the border of the meatus they are also termed as parameatal cysts [3]. Lesion is usually asymptomatic, but can be complicated by infection or trauma [2,4]. It is thought that cysts of the median raphe to arise from embryologic developmental defects of the male urethra [1][2][3]. Histologically the cyst does not communicate with the urethra and is lined by a pseudostratified, columnar or stratified squamous cell epithelium, similar to urethral transitional epithelium [2,5]. The luminal cells may present with minimal secretion [6,7]. Therefore the lesion can be misinterpreted as an apocrine hydrocystoma or cystadenoma [6,7].

Case Report
We present a 20-year old man with an asymptomatic nodule on the ventral surface of the penis. Physical examination revealed round, painless, soft nodule, 0.9 cm in diameter on the ventral surface of the penis, just proximal to the glans ( Figure 1). There was no history of trauma or infection. In this case, because of problems during sexual intercourse was treated surgically this change on the penis.
Histolopathological examination showed unilocular cystic cavity within the corium, lined by columnar, partially pseudostratified epithelium with occasional mucinous cells ( Figure 2). The lumen was empty. There was no epithelial atypia or inflammatory infiltrate. abnormality of the male genitalia [1,2,8,9]. Several histogenetic explanations have been suggested; abnormal formation of epithelial buds from the urethral epithelium that became sequestrated and independent after closure of the medium raphe, incomplete fusion of the urethral folds and cystic dilatations of ectopic Littré's periurethral glands [2,3].
The cysts develop mainly on the ventral surface of the penis [1,2,5], mostly near the glans, but can occur anywhere from the urinary meatus to the anus. They are seldom pigmented [8] or present as a perianal polyp [9]. Usually they are asymptomatic and complications are possible only to care of. In that care it should be (surgically treated) [2].
Differential diagnosis includes dermoid cyst or epidermal cyst, glomus tumor, pilonidal cyst, urethral diverticulum, and steatocystoma [2]. Differentiation is possible on the base of histological findings typical for median raphe cyst, a single cystic cavity with no urethral communication and lined by a columnar pseudo-stratified epithelium [1]. However, differentiating median raphe cyst from apocrine hidrocystoma could be difficult. Several reports of apocrine cystadenoma of the penis could, in fact, represent cysts of the median raphe [6,7]. The absence of a basal layer of cuboidal, myoepithelial cells, and the absence of true decapitation secretion are very important in differentiating those two entities [10]. Apocrine cystadenomas have the presence of smooth muscle actin (SMA) positive cells, and an apical border of luminal cells and are regularly stained by anti-human milk fat globule (anti-HMFG), a peripheral layer of S100 protein [7].
The lining epithelium varies according to the segment origin of the urethra of the lesion, i.e., stratified in the distal part (ectodermal origin) and columnar pseudostratified in the remainder of the urethra (endodermal origin) [2]. In conclusion, we have presented a medium raphe cyst case whose study supports its histogenetic relationship with the urothelium.

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