3 June 2009 – Case of the Week #148


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Case of the Week #148


Clinical History


A 59 year old man presented with a left testicular mass which had been growing slowly for a year.  He had a history of a left testicular hydrocelectomy in 2005.  His serum AFP levels were normal, and an orchiectomy was performed.


Sectioning revealed a 4.8 x 4.6 x 3.6 cm yellow, partially cystic firm mass pushing the testicular parenchyma to the edge.  The mass was firmly attached to the tunica vaginalis.


Gross images: #1;  #2


Micro images: low power;  high powercalretinin #1#2;  WT1


What is your diagnosis?




























Malignant mesothelioma of the tunica vaginalis




The tumor had an invasive, tubulopapillary pattern, with a single layer of atypical, epithelioid-type mesothelium overlying a fibrovascular core.  No sarcomatoid features were identified.  Tumor cells were immunoreactive for calretinin and WT1 (nuclear staining), and negative for Ber-EP4, MOC31, CEA, desmin and AFP.  This is consistent with the staining pattern for malignant mesotheliomas in the testis (calretinin+, EMA+, thrombomodulin+, CK7+, CK5/6 variable, CK20-, CEA-, Am J Surg Pathol 2006;30:1).


Mesotheliomas are neoplasms of the lining of the body’s serous cavities, usually involving the pleura, but occasionally the peritoneum or pericardium (eMedicine).  In the testis, the tunica vaginalis (image) derives from evagination of peritoneum into the scrotum.  Mesotheliomas at this site are rare, with a wide age range (AJSP 1995;19:815).  Most cases are associated with asbestos exposure (Orphanet J Rare Dis 2008 Dec 19;3:34), although some cases, including the present one, have no history of asbestos exposure (Cases J 2008 Nov 14;1:310).  Of note, mesotheliomas often present with a hydrocele, as in this case.


The differential diagnosis includes:


• adenocarcinoma - more common in the epididymis than the tunica vaginalis, has back to back glands or a poorly differentiated pattern, often necrosis and mitotic figures, CK20+, BerEp4+, 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


Malignant mesothelioma of the tunica vaginalis is often fatal.  Treatment includes radical orchiectomy and possibly retroperitoneal lymph node dissection.  Even patients with negative resection margins frequently die of disease.  In a recent study of 5 patients, mean disease specific survival was only 29 months, and 3 patients developed inguinal nodal metastases (Urology 2005;66:397).



Nat Pernick, M.D., President

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