Testis and epididymis
Epididymal tumors

Author: Swapnil U. Rane, M.D. (see Authors page)

Revised: 24 May 2017, last major update December 2014

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Mesothelioma [title] epididymis

Cite this page: Mesothelioma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/testisepidmesothelioma.html. Accessed April 27th, 2018.
Definition / general
  • Arises from the tunica vaginalis, often in relation to the epididymis, testis or spermatic cord
Clinical features
  • Often presents as hydrocele with or without associated painless mass
  • Bilateral tumors are rare, ~4% of cases (Cancer 1998;83:2437)
  • Other presentations include inguinal hernia, epididymitis or testicular mass
Radiology description
  • Ultrasound reveals hydrocele with thickened wall with hypoechoic nodule over epididymis / tunica vaginalis
Prognostic factors
  • Complete / adequate excision improves disease free survival; lower recurrence rate after radical orchiectomy (~10%) versus simple hydrocele sac excision (~30%) (Cancer 1998;83:2437)
  • Better outcome in younger patients
  • Metastases at time of presentation associated with worse prognosis
  • Well differentiated papillary mesothelioma has better prognosis than undifferentiated spindle cell mesothelioma
  • Other prognostic factors include tumor size, lymph node metastases, invasion into adjacent structures, degree of differentiation
Case reports
  • Radical orchiectomy is standard treatment
  • If treated with transcrotal surgery, subsequent hemiscrotectomy or hemiscrotal irradiation is often recommended
  • Retroperitoneal lymph node dissection is recommended only if pre-op workup reveals suspicious nodes
  • Well differentiated papillary mesothelioma may be treated with only surgery
Clinical images

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Small nodules

Gross description
  • Multiple nodules within hydrocele sac, frequently associated with mass infiltrating spermatic cord, epididymis or testis
  • May be a solitary nodule
  • Hydrocele sac is thick walled, often containing hemorrhagic fluid and papillary excrescences
  • Less often, mesothelioma creeps along tunica without forming a mass-like lesion
Gross images

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Radical orchiectomy specimen

Nodular mass at spermatic cord

Microscopic (histologic) description
  • Same as mesothelioma at other sites
  • Either epithelial (60 - 70%), spindle cell (least common) or biphasic type (30 - 40%)
  • Epithelial type has papillary, tubular, adenomatoid or solid architectural patterns
  • Biphasic type has fascicles of spindle cells with scanty stroma, often merging with epithelial cells
  • Most well differentiated tumors shows predominance of epithelial type
  • Stroma may be desmoplastic or show necrosis
Microscopic (histologic) images

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Epithelial tumor cells

Glandular pattern in desmoplastic stroma

Malignant mesothelial tubular structures

Biphasic exophytic nodule

Papillary structures

Coagulative necrosis

Mesothelioma of uncertain malignant potential


CK+, calretinin+, CEA-

CK5 / 6+, calretinin+, vimentin+

AE1 / 3+, CAM 5.2+, calretinin+, WT1+

Various stains

Cytology description
  • Moderately cellular smears; well differentiated tumors have papillary clusters of epithelial cells with minimal atypia
Negative stains
Electron microscopy description
  • Cells showing both epithelial and mesenchymal differentiation
  • Presence of numerous microvilli on luminal surfaces with length to breadth ratio of > 10