Dermatology

Median Raphe Cyst [genitoperineal raphe cyst, mucous cyst of the penis, or parameatal raphe cyst)

Median Raphe Cyst [genitoperineal raphe cyst, mucous cyst of the penis, or parameatal raphe cyst]

Are You Confident of the Diagnosis?

The diagnosis of median raphe cysts can be made with confidence by history, physical examination, and histologic evaluation.

What you should be alert for in the history

Patients typically present with one or more asymptomatic nodules on the ventral side of the penis. They may complain of tenderness, pain, and/or purulent discharge if there is associated infection, most commonly with Staphylococcus aureus or Neisseria gonnorrhoeae, or as a result of trauma. In addition, if located near the urethral meatus, some patients may complain of obstructive urinary symptoms. Some reports describe sexual interference depending on location and size of the cyst.

Characteristic findings on physical examination

Median raphe cysts appear as skin-colored to translucent cystic papules, nodules, or cords located in the midline from the urethral meatus to the anus. The distal penis is the most common location reported. They are typically a few millimeters in diameter but may be up to several centimeters long in the canaliform variant. Median raphe cysts are often freely mobile and non-tender to palpation.

Expected results of diagnostic studies

Histologically, median raphe cysts reveal a single cystic space located in the dermis lined by one of two types of epithelium: stratified squamous epithelium or pseudostratified columnar epithelium (Figure 2), the latter being the most common. The majority of cysts have only one type of epithelium, while some may have areas of both. Some may show decapitation secretion resembling apocrine differentiation. Rarely, a ciliated lining has been reported. They do not communicate with the urethra.

Figure 1.

Skin-colored papule in the midline on the ventral surface of the penis.

Figure 2.

Median raphe cyst: small cystic space lined by a pseudostratified columnar epithelium.

The epithelium stains for Cytokeratin 7 (CK7) and carcinoembronic antigen (CEA) and commonly with Cytokeratin 13, but it does not stain for S-100, Cytokeratin 20, or human milk fat globulin 1 (HMFG1), the latter helping to distinguish median raphe cysts from an apocrine cystadenoma.

Diagnosis confirmation

The clinical differential diagnosis includes steatocystoma, molluscum contagiosum, pilonidal cyst, dermoid cyst, epidermoid cyst, and urethral diverticulum. These entities can be easily distinguished on histologic grounds. Urethral diverticuli can be diagnosed using voiding and retrograde cystourethrography.

Who is at Risk for Developing this Disease?

Median raphe cysts occur only in males. Although they are congenital, they are typically discovered for the first time in adolescent boys and some may not come to medical attention until adulthood, when they enlarge or become symptomatic.

What is the Cause of the Disease?

Etiology

Pathophysiology

Median raphe cysts are thought to arise from an abnormality in the formation of the urethra whereby embryonic nests persist during invagination and closure of the urogenital folds. Another theory holds they may form from ectopic Littre’s (periurethral) glands.

Systemic Implications and Complications

There are no reported systemic implications associated with median raphe cysts. They can, however, become infected with S aureus or N gonnorrhoeae causing swelling, pain and purulent discharge.

Treatment Options

Expectant Management

- If small and asymptomatic

Medical Therapy

- Systemic antibibiotics to cover S. aureus and/or N. gonnorrhoeae if clinically infected

Surgical Therapy

- Surgical excision with primary closure if symptomatic or of cosmetic concern.

Optimal Therapeutic Approach for this Disease

When treatment is required, surgical excision followed by primary closure is the treatment of choice. This procedure can be performed under local, spinal, or general anesthesia, depending on the patient and size of the lesion. If clinical infection is present, excision should be postponed until after successful treatment of the infection.

Patient Management

If expectant management is chosen, the patient and/or family should be informed the cyst may enlarge slowly and, rarely, quickly over time, it may become infected and surgical excision can occur any time in the future. The recurrence rate following surgical excision is extremely low.

Unusual Clinical Scenarios to Consider in Patient Management

Rarely, median raphe cyst will present as a rapidly growing nodule, at times following sexual intercourse.

What is the Evidence?

James, WD, Berger, TG, Elston, DM. Andrews' diseases of the skin. Saunders-Elsevier. 2006. pp. 682.

(Excellent review of the salient features of median raphe cysts including clinical presentation, histologic findings, and treatment.)

Navarro, HP, Lopez, PC, Ruiz, JM, Martinez Sanchiz, C, Cha, SH, Sanchez, AS. "Median raphe cyst. Report of two cases and review of the literature". Arch Esp Urol. vol. 62. 2009. pp. 585-9.

(Excellent overview of median raphe cysts, including histologic and immunohistochemical findings.)

Verma, SB. "Canal-like median raphe cysts: an unusual presentation of an unusual condition". Clin Exp Dermatol. vol. 34. 2009. pp. e857-8.

(Report of two cases of an uncommon canaliform presentation of median raphe cysts accompanies a brief review of the diagnosis. Although there was not histologic confirmation of these cysts, this paper raises awareness of this unusual clinical appearance.)

Koga, K, Yoshida, Y, Koga, M, Takeshita, M, Nakayama, J. "Median raphe cyst with ciliated cells of the penis". Acta Derm Venereol. vol. 87. 2007. pp. 542-3.

(Case report of the rare histologic finding of a pseudostratified ciliated columnar epithelial lining of a median raphe cyst. This report raises awareness of this unusual histologic finding.)

Giannakopoulos, S, Makris, NE, Kalaitzis, C, Papatsoris, AG, Pantazis, T, Touloupidis, S. "Two unusual cases of median raphe penile cysts". Eur J Dermatol. vol. 17. 2007. pp. 34.

(Description of presentation following sexual intercourse and another of a large cyst creating difficulties w/ sexual intercourse. Case descriptions accompanied by a brief review of the salient features of median raphe cysts including immunohistochemical findings and treatment.)

Dini, M, Baroni, G, Colafrancheschi, M. "Median raphe cyst of the penis: a report of two cases with immunohistochemical investigation". Am J Dermatopathol. vol. 23. 2001. pp. 320-4.

(Report of two cases of immunohistochemical staining for cytockeratins, carcinoembryonic antigen, dynein, chromagranin and synaptophysin. Both cases stain positively for CK7 and 13, as well as CEA, indicating immature uroepithelial metaplasia and dysembryogenetic cloacal nature of the cysts.)

Ohnishi, T, Watanabe, S. "Immunohistochemical analysis of human milk fat globulin 1 and cytokeratin expression in median raphe cyst of the penis". Clin Exp Dermatol. vol. 26. 2001. pp. 88-92.

(Excellent report of immunohistochemical findings of nine cases of clinically definite median raphe cysts. Staining for several cytokeratins, human milk fat globulin 1 (found in apocrine cystadenoma of the penis) and smooth muscle acting were evaluated. Only one case stained positively for HMFG; this was limited and focal only, whereas all apocrine cystadenomas stained positively in a previous study. Absence of HMFG staining may be a useful tool to differentiate median raphe cyst from apocrine cystadenoma.)
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