COW-2020-17

CASE OF THE WEEK

2020-17 / April 27
(Contributor: Ankur Sangoi)

A 55-year-old man presented with paratesticular pain and swelling. A hydrocelectomy was performed.

Quiz

1. What is the correct diagnosis?

a. Adenomatoid tumor

b. Mesothelioma

c. Rete testis adenocarcinoma

d. Florid mesothelial hyperplasia of the tunica vaginalis

1. Florid mesothelial hyperplasia of the tunica vaginalis

Immunostains performed on this case showed lesional cells with strong calretinin reactivity, low Ki67 proliferation index (<2%), wild-type p53 staining, and intact BAP1 staining. Follow-up (2 years) showed no recurrences.

The main differential diagnosis includes florid mesothelial hyperplasia of the tunica vaginalis (reactive process secondary to persistent serosal injury in hydroceles and hernia sacs) and mesothelioma. Mesothelioma often shows gross nodules or irregular thickening of the hydrocele wall. Histologically, mesothelioma shows expansile, complex, and irregular formations with destructive invasion and more frequent mitotic activity. Although florid mesothelial hyperplasia can impart an “infiltrative” appearance especially when entrapped mesothelial cells occur deep within fibrous tissue, it typically shows a linear array of widely spaced architecturally simple cell clusters lacking severe atypia/increased mitoses and can show variable chronic inflammation. Ancillary studies can be used in this differential diagnosis, with positivity for p53, positivity for GLUT1, loss of BAP1 stain, high Ki67 proliferation index, and 9p21 FISH deletion all supportive clues to a diagnosis of mesothelioma.

1. Lee S, Illei PB, Han JS, Epstein JI. Florid mesothelial hyperplasia of the tunica vaginalis mimicking malignant mesothelioma: a clinicopathologic study of 12 cases. Am J Surg Pathol. 2014 Jan;38(1):54-9.

1. Lee S, Illei PB, Han JS, Epstein JI. Florid mesothelial hyperplasia of the tunica vaginalis mimicking malignant mesothelioma: a clinicopathologic study of 12 cases. Am J Surg Pathol. 2014 Jan;38(1):54-9.

Testis

Florid mesothelial hyperplasia, tunica vaginalis