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12 December 2012 - Case of the Week #261

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Thanks to Dr. Chungja C. Shim, Titusville Area Hospital, Pennsylvania (USA), for contributing this case. To contribute a Case of the Week, follow the guidelines on our Case of the Week page.

This month’s recommended article
by the Editors of Modern Pathology:

Reproducibility of histopathological subtypes and invasion in pulmonary adenocarcinoma.
An international interobserver study

Click here to view article.


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Case of the Week #261

Clinical History:

A 11 year old boy was initially seen for a left hydrocele. Ultrasound showed only the hydrocele.

At surgery, multiple papillary lesions were present on the tunica, which were biopsied. An orchiectomy was performed.

Intraoperative images:


Micro images:

What is your diagnosis?


Malignant papillary mesothelioma of testicle (invasive)



Left to right: calretinin+, WT1+, Mesothelin+, BerEP4-

The orchiectomy specimen showed multifocal involvement of the papillary tumor on the external surface with no testicular parenchymal involvement.

Immunohistochemistry indicated that the tumor was diffusely positive for Calretinin, WT1 and Mesothelin, as well as CD56, CK7 and CA125, with focal staining for EMA, p16, CK5/6 and p53 and negative staining for desmin, MOC31, C-kit and BerEP4.

Mesothelioma of the testis originates from the tunica vaginalis, which derives from evagination of the peritoneum into the scrotum. This rare entity has a mean age of 54 years, but can occur in children (Am J Surg Pathol 1995;19:815, Mod Pathol 2010;23:1165). It is associated with asbestos exposure (BJU Int 2012;110:533, Cancer 1998;83:2437), and often presents with hydrocele.

It has a papillary or tubulopapillary pattern with a single layer of atypical mesothelium overlying a fibrovascular core. The tumor cells are typically epithelioid, not spindled. Stromal invasion is present, and psammoma bodies are variable. Mesotheliomas of the testis, as at other sites, are immunoreactive for calretinin, EMA, thrombomodulin and CK7, and negative for CK20 and CEA (Am J Surg Pathol 2006;30:1).

The differential diagnosis includes:

Adenocarcinoma: more common in the epididymis than in the tunica vaginalis, back to back glands or a poorly differentiated pattern, often necrosis and mitotic figures, CK20+, CEA+, calretinin-, thrombomodulin-, no long thin microvilli on EM
Well differentiated papillary mesothelioma: very rare, papillary but not tubular, papillae are lined by cuboidal cells with a complex branching pattern but no atypia and no invasion; stroma has lymphoplasmacytic infiltrate
• Mesothelial hyperplasia: no mass, no complex arborizing papillae, not invasive

Treatment is radial orchiectomy, but these tumors are aggressive, and the median survival is only 1-2 years (
Arch Pathol Lab Med 2012;136:1).

Nat Pernick, M.D., President
and Palak Thakore, Associate Medical Editor
PathologyOutlines.com, Inc.
30100 Telegraph Road, Suite 408
Bingham Farms, Michigan (USA) 48025
Telephone: 248/646-0325
Email: NatPernick@Hotmail.com
Alternate email: NatPernick@gmail.com