Testis & paratestis

Mesothelial tumors

Adenomatoid tumor

Editor-in-Chief: Debra L. Zynger, M.D.
Sarah Findeis, M.D.
He Huang, M.D., Ph.D.

Last author update: 28 January 2020
Last staff update: 15 November 2023

Copyright: 2002-2023, PathologyOutlines.com, Inc.

PubMed Search: Adenomatoid tumor testis

Sarah Findeis, M.D.
He Huang, M.D., Ph.D.
Page views in 2022: 20,230
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Cite this page: Findeis S, Huang H. Adenomatoid tumor. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/testisepidadenomatoid.html. Accessed November 29th, 2023.
Definition / general
Essential features
  • Most common benign paratesticular tumor
  • Usually based in the epididymis and well circumscribed
  • Expresses markers typical of mesothelial origin
ICD coding
  • ICD-10: D29.30 - benign neoplasm of unspecified epididymis
  • Testicular adnexa
  • Not known
  • Not known
Clinical features
  • Primarily made histologically
  • Testicular tumor markers: normal
Radiology description
  • Circumscribed, solid paratesticular mass
  • Unable to distinguish benign versus malignant on sonography (Radiology 1997;204:43)
  • Tumors of the tunica may be indistinguishable from a germ cell tumor by imaging
Radiology images

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Coronal MR


Prognostic factors
  • Benign neoplasm
Case reports
  • Surgical excision
  • Intraoperative frozen section may be helpful to indicate testis sparing surgery
Gross description
Gross images

Contributed by Debra L. Zynger, M.D.

Paratesticular tumor

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Well circumscribed tumor

Frozen section description
  • May be confused for malignant mesothelioma on biopsy; gross correlation often needed
  • Can have atrophic testes with fibrous stromal proliferation (Urology 2004;63:779)
Frozen section images

Contributed by Debra L. Zynger, M.D.

Distorted, compressed tubules

Spindle cell appearance Spindle cell appearance

Spindle cell appearance

Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Sarah Findeis, M.D., Stephanie J. Conrad, M.D., Ming Zhou, M.D.,
the Genitourinary Pathology Society (GUPS) and @katcollmd on Twitter

Interface with testis

Cords and trabeculae pattern

Eosinophilic cells


CK AE1/3

Circumscribed tumor

Dilated cystic spaces

Vacuolated and attenuated epithelium

Bland nuclei


Adenomatoid tumor Adenomatoid tumor Adenomatoid tumor Adenomatoid tumor

Adenomatoid tumor

Virtual slides

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Adenomatoid tumor

Cytology description
  • Epithelioid, monolayered sheets or clusters of cells with eccentric, vesicular round to ovoid nuclei, granular chromatin and pale / vacuolated cytoplasm (J Cytol 2009;26:30, J Cytol 2013;30:65)
  • Can have a background of naked nuclei as well as stromal cells (Acta Cytol 1989;33:6)
Cytology images

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Moderate cellularity

Monolayered sheets of cells

Negative stains
Electron microscopy description
  • Rich in cytoplasmic organelles and has superficial desmosomes with microvilli (Cancer 1972;30:244)
Molecular / cytogenetics description
Sample pathology report
  • Testicle and spermatic cord, right, radical orchiectomy:
    • Paratesticular adenomatoid tumor, 1.5 cm
    • Margins widely free of tumor (> 5.0 cm)
    • Unremarkable background testis, epididymis and spermatic cord
    • Comment: The tumor is positive for AE1/3, WT1 and calretinin and is negative for SALL4 and inhibin.
Differential diagnosis
Board review style question #1

    Which is true regarding this paratesticular entity which does not involve the testicular parenchyma?

  1. Exclusively identified within men
  2. Malignant transformation occurs in 50% of cases
  3. Most common in the sixth to seventh decade
  4. Rarely identified within the testicular parenchyma
Board review style answer #1
D. These tumors are rarely identified within the testicular parenchyma. This is an adenomatoid tumor. They can be identified within both sexes. It occurs in the paratesticular region most commonly in the third to fourth decade. The tumor rarely involves the testicular parenchyma. If there is only intraparenchymal involvement, other primary parenchymal lesions need to be ruled out, such as a sex cord stromal tumors or germ cell tumors.

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Reference: Adenomatoid tumor
Board review style question #2

    A 36 year old man presents to his physician with a painless testicular mass. Imaging showed a well circumscribed solid mass arising from the tunica albuginea and not involving the testicular parenchyma. An orchiectomy is performed which shows a 2.0 cm unencapsulated white-tan circumscribed nodule. Histologic examination shows cords and tubules of cuboidal eosinophilic cells with vacuolated cytoplasm in the background of fibrous stroma, which infiltrates into the surrounding testicular tubules. What is the most likely staining pattern for this lesion?

  1. Calretinin +, EMA +, BAP 1+
  2. CK AE1/3 -, CD31 +, CD15 +
  3. OCT3/4 +, CEA+, S100+
  4. Vimentin -, CD99 +, calretinin -
Board review style answer #2
A. Calretinin +, EMA +, BAP 1+. This is an adenomatoid tumor, which is of mesothelial origin as the staining pattern suggests. The patient presentation of a small painless mass in a patient in the third - fourth decade is typical. Adenomatoid tumors rarely involve the testicular parenchyma and are the most common paratesticular tumor. Microscopic infiltration may be misinterpreted as invasion but may occur and the tumor still has a benign course.

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Reference: Adenomatoid tumor
Board review style question #3
    Which of the immunohistochemical stains, when positive, supports the diagnosis of adenomatoid tumor?

  1. AFP
  2. B72.3
  3. Calretinin
  4. CD34
  5. Inhibin
Board review style answer #3
C. Calretinin

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