Home Education AUAUniversity Education Products & Resources Pathology for Urologists Paratesticular Tumors Malignant Mesothelioma

Malignant Mesothelioma (MM)

Image A

Image B

  • Arise from mesothelial cells of tunica vaginalis.
  • Rare, but represents the 2nd most common paratesticular tumor.
  • Wide age range: 6-90 years old (ave. 54 years).
  • Similar to thoracic cases, asbestos exposure is also a risk factor (only in <50%).
  • Presents as paratesticular enlargement and may be associated with hydrocele.
  • Gross: Diffuse thickening of tunica vaginalis with multiple friable nodules or papillary excrescences; may invade into testis.

Image C

Image D

  • Histology:
    • Similar to mesothelioma of other serosal sites.
    • Pure epithelial (60-70%) (image A), (image B), (image C), & (image D) or biphasic epithelial and stromal (30-40%).
    • Well-differentiated tumors show papillary or tubulopapillary (most common), glandular and poorly differentiated tumors show solid growth.
    • Tumor cells are round or cuboidal, with mild to moderate pleomorphism and prominent nucleoli.
    • Cytologic atypia or mesothelial proliferation may not be diagnostic: invasion to tunica vaginalis key.
  • Immunohistochemistry: Positive for mesothelial-associated markers (calretinin+, WT1+ and CK5/6+).
  • Aggressive tumors with a bad habit of recurring and metastasizing late; may recur in abdominal or thoracic serosa.
  • DDX: reactive mesothelial hyperplasia: often seen inflamed hernia sac; cytologically may look similar to MM but lacks invasion.