Epididymal Cyst in a Teenager

Specimen Type:

Epididymis

History:

A 12-year-old boy presented with a cystic mass in the head of the right epididymis. At gross description, the lesion consists of an intact cyst measuring 3 cm in maximum diameter. On piercing the content is composed of clear fluid. No internal loculations or solid areas identified. Representative cross-sections were submitted.

Pathologic Features:

Sections show part of the epididymis and a cyst with a thin fibrous wall lined by columnar ciliated epithelium without atypia or true stratification (Figures 1-2). In one area, a small tube-like structure with surrounding concentric smooth muscle is noted (Figure 3). Adjacent to this the epithelium lining the cyst is slightly more papillary in nature with infoldings (Figures 4).

Differential Diagnosis:

  • Papillary cystadenoma of epididymis
  • Simple epididymal cyst
  • Appendix epididymis (vestigial caudal mesonephric collecting tubule)
  • Paradidymis (organ of Giraldes)
  • Vasa aberrans (organ of Haller)
  • Hydrocele
  • Spermatocele
  • Benign papillary mesothelioma

Papillary cystadenoma of epididymis: Papillary cystadenoma of epididymis is a benign tumor that accounts for about 1/3 of all primary epididymal tumors. It appears as a cystic mass in the head of the epididymis and is bilateral in about 40%. It consists of dilated ducts lined by papillae with a single or a double layer of cuboidal to low columnar ciliated epithelium. About 2/3 of cases of papillary cystadenoma of the epididymis occur in patients with von Hippel-Lindau syndrome, and they are more frequently bilateral in this syndrome.

Simple epididymal cyst: Epididymal cysts are often very difficult to differentiate from spermatoceles, and definitive differentiation depends on aspiration of the cystic fluid. If sperm is present, the cystic mass is a spermatocele. If no sperm is present, the mass is probably an epididymal cyst.

Appendix epididymis (vestigial caudal mesonephric collecting tubule): The appendix epididymis is a pedunculated spherical cystic or elongate structure arising from the anterosuperior pole of the head of the epididymis. Microscopically, it is lined by cuboidal to low columnar epithelium which may be ciliated and show secretory activity. The wall consists of loose connective tissue and is covered on its outer surface by flattened mesothelial cells that are continuous with the visceral tunica vaginalis. It may become dilated by serous fluid and mimic a tumor.

Paradidymis (organ of Giraldes): This wolfian duct embryonic remnant consists of clusters of tubules lined by cuboidal to low columnar epithelium within the connective tissue of the spermatic cord, superior to the head of the epididymis.

Vasa aberrans (organ of Haller): These wolfian ducts remnants appear as clusters of tubules that are histologically similar to the paradidymis. They arise within the groove between the testis and epididymis.

Hydrocele: A hydrocele is a collection of watery fluid around the testicle. This is a common problem in newborn males and usually goes away within the first year of life. When the testicle drops into the scrotum (about the eighth month of pregnancy), a sac (the processus vaginalis) from the abdominal cavity travels along with the testicle. Fluid can then flow to the scrotum to surround the testicle. This sac usually closes and the fluid is absorbed. Hydrocele is lined by a single layer of cuboidal or flattened mesothelial cells, sometimes with prominent atypia, with underlying connective tissue stroma.

Spermatocele: A spermatocele is a benign cystic accumulation of sperm often found in the head of the epididymis that usually presents as a smooth, firm, well-circumscribed mass along the testis. Spermatoceles are considered in the differential diagnosis of any scrotal mass and must be differentiated from hydroceles, varicoceles, epididymal cysts, and other scrotal masses.

Benign papillary mesothelioma: Benign papillary mesothelioma of the tunica vaginalis usually appears in young men and consists of a hydrocele sac with papillary excrescences and cystic and solid areas. Microscopically, there are complex papillae covered by cuboidal, columnar, or flattened mesothelial cells with large vesicular nuclei and glassy eosinophilic cytoplasm.

Diagnosis:

Papillary cystadenoma of epididymis.

Key Features:

  • Benign, familial, unilateral or bilateral (40%)
  • Mean age 36 years
  • Associated with von Hippel-Lindau (VHL) disease; 65% with bilateral tumors have VHL vs. 18% with unilateral lesions
  • High levels of vascular endothelial growth factor mRNA by in situ hybridization in one patient with bilateral tumors
  • Gross: well circumscribed, 1-5 cm, papillary fronds of gray-brown-yellow tissue project into cystic space
  • Micro: papillary infoldings project into cystic spaces covered by cuboidal/columnar cells; tubules common, colloid type cystic material common; tumor cells have lightly eosinophilic to clear cytoplasm; may see dilated efferent ductules; may have clear cells resembling metastastic renal cell carcinoma
  • Positive stains: AE1/AE3, alpha-1-antitrypsin, alpha-1-antichymotrypsin, Cam5.2, EMA, vimentin, CEA variable, vascular endothelial growth factor
  • In some cases, may mimic metastatic clear cell renal cell carcinoma. Serous borderline tumors (atypia, mitotic activity, stratification, detached cell clusters) need to be ruled out as well.

References:

  1. Kuhn MT, Maclennan GT.Benign neoplasms of the epididymis.J Urol. 2005 Aug;174(2):723.
  2. Aydin H, Young RH, Ronnett BM et al. Clear cell papillary cystadenoma of the epididymis and mesosalpinx: immunohistochemical differentiation from metastatic clear cell renal cell carcinoma.Am J Surg Pathol. 2005 Apr;29(4):520-3.
  3. Jones EC, Murray SK, Young RH. Cysts and epithelial proliferations of the testicular collecting system (including rete testis).Semin Diagn Pathol. 2000 Nov;17(4):270-93.
  4. Leung SY, Chan AS, Wong MP et al. Expression of vascular endothelial growth factor in von Hippel-Lindau syndrome-associated papillary cystadenoma of the epididymis.Hum Pathol. 1998 Nov;29(11):1322-4.
  5. Gilcrease MZ, Schmidt L, Zbar B et al. Somatic von Hippel-Lindau mutation in clear cell papillary cystadenoma of the epididymis.Hum Pathol. 1995 Dec;26(12):1341-6.