Testicular Mass in an Adult

Specimen Type:



A 61-year-old man underwent a hydrocelectomy after incidental finding of multiple masses in the testis. Submitted tissue is membranous with soft tan-pink fine papillary areas on the surface. The largest lesion measures 2.7 x 1.9 x 0.9 cm.

Pathologic Features:

The sections reveal multiple papillary lesions attached to the wall of hydrocele sac with a pushing interface with the underlying stroma (Figures 1, 2). The lesion mainly consists of complex branching papillae although tubules and solid patterns are also seen (Figures 3, 4, 5). The fibrovascular cores are hyalinized, hemorrhagic and edematous (Figure 6). The papillae are covered by a single layer of cells with bland cytologic features (Figures 7, 8). The tumor cells are positive for vimentin and cytokeratin (AE1/AE3) (Figures 9, 10). No prominent spindle cell component identified. No stromal invasion is present.

Differential Diagnosis:

  • Mesothelial hyperplasia
  • Malignant mesothelioma

Mesothelial hyperplasia: This is a common form of pseudotumor that occurs in hydrocele sacs, hernia sacs, and diverse other testicular and adnexal structure. In contrast to other pseudotumors, it is almost invariably an incidental finding on microscopic examination. It is more commonly identified in older patients who more frequently undergo hydrocelectomy. Microscopically, the overall picture is usually of nonspindled mesothelial cells. Small tubular, cord-like, and papillary patterns may be seen. The aggregates of mesothelial cells generally do not invade into underlying tissues to any appreciable degree. There may be mild nuclear pleomorphism, but the overall nuclear features are bland and mitotic figures rare; an associated inflammatory background often points to a reactive process.

Malignant mesothelioma: Malignant mesotheliomas of the tunica vaginalis are often associated with a hydrocele, which may recur after repeated tapping. The diagnosis of a neoplasm is often not apparent until the time of exploration. Gross examination typically reveals a tumor coating the tunica vaginalis or multiple nodules studding it. The tumor may infiltrate into the adjacent soft tissue. Microscopic examination reveals patterns similar to those encountered in malignant mesotheliomas of the pleural or peritoneal cavity. Approximately, 75% of the tumors are epithelial and 25% biphasic. The epithelial tumors are typically papillary or tubulopapillary. Although often predominantly exophytic and noninvasive, at least focal infiltration of the wall of a hydrocele sac or the tunica occurs in most cases. The papillae often have thick fibrovascular cores which are occasionally hyalinized. The neoplastic cells are typically cuboidal and relatively uniform with scant to moderate amounts of eosinophilic cytoplasm.


Well differentiated papillary mesothelioma

Key Features:

  • Grossly: Single or multiple nodules coating tunica vaginalis, often associated with hydrocele
  • Microscopically:
    • Epithelial or biphasic tumor
    • No stromal invasion
    • Papillary and/or tubular growth pattern
    • Bland-looking neoplastic cells
  • Immunohistochemically: Coexpression of vimentin and keratin

Comment: The mesothelioma should be distinguished from florid mesothelial hyperplasia; the presence of a mass with typical studding of a hydrocele sac is incompatible with the diagnosis of mesothelial hyperplasia which is almost invariably a microscopic finding only. In addition, mesothelial hyperplasia does not exhibit the complex, arborizing, papillary, fibrous stalks of papillary mesothelioma. On the other hand, lack of stromal invasion argues against classic malignant mesothelioma. Therefore, the tumor presented here is classified as well differentiated papillary mesothelioma (WDPM) (references 1).

Recently, WDPM has emerged as a distinct clinicopathologic entity in the paratesticular region, and it is a multifocal mesothelial proliferation and often presents with recurrent hydrocele. WDPM of paratesticular region is rare with only a handful of published case reports (references 2, 3). Although the long-term behavior of the paratesticular WDPM remains uncertain, this lesion appears to be more indolent than the true malignant mesothelioma (reference 2). Rare cases of WDPM can progress to malignant mesothelioma, leading to its classification as a tumor of low malignant potential. Excellent survival outcomes may be achieved with aggressive surgical intervention.


  1. J.N. Eble, World Health Organization. Pathology and genetics of tumours of the urinary system and male genital organs, IARC Press, Lyon, France (2004).
  2. Tolhurst SR, Lotan T, Rapp DE, et al. Well-differentiated papillary mesothelioma occurring in the tunica vaginalis of the testis with contralateral atypical mesothelial hyperplasia. Urol Oncol. 2006 Jan-Feb; 24 (1):36-9.
  3. Chetty R. Well differentiated (benign) papillary mesothelioma of the tunica vaginalis. J Clin Pathol. 1992 Nov;45(11):1029-30.