2019-3 / MARCH 4

A 25 year old man was found to have a 5.0 cm. paratesticular mass.


What is the correct diagnosis?

a) De-differentiated liposarcoma

b) Synovial sarcoma

c) Malignant mesothelioma

d) Rhabdomyosarcoma

Q1. B

Synovial sarcoma

The tumor is biphasic. The spindle cell component consists of short fascicles of cellular spindle cells. Despite very high cellularity and cells having a high N/C ratio, imparting a very “blue” appearance at low magnification, there is relative uniformity in the atypia with a lack of pleomorphism. Focally, there are areas of collagen deposition. In addition, there is gland formation which is an integral component of the tumor. The cells within the glands are atypical and have similar cytology to the spindle cells. The tumor was focally pancytokeratin positive and on the outside stains was focally positive for inhibin and calretinin. S100 protein was negative. Given the morphology, molecular studies were performed and showed a translocation t(X;18)(p11;q11), consistent with synovial sarcoma. In an adult, the most common malignant spindle cell tumor in the paratesticular region would be a de-differentiated liposarcoma. However, these tumors in addition to having a well-differentiated liposarcoma component, would show greater pleomorphism and an haphazard array of the tumor cells. Rhabdomyosarcoma is the most common paratesticular malignant tumor in childhood and one of the variants is “spindle cell rhadomyosarcoma” which could mimic the spindle cell component in the current case, yet would lack a glandular component. The spindle cell component of a biphasic malignant mesothelioma would be more fibrous and not as monotonous and cellular. There are no cases reported as paratesticular synovial sarcomas, although the one reported case of a testicular synovial sarcoma is not clear whether it was intratesticular or paratesticular.

Testicular synovial sarcoma: a case report.
Nesrine M, Sellami R, Doghri R, Rifi H, Raies H, Mezlini A.
Cancer Biol Med. 2012 Dec;9(4):274-6.

Jonathan I. Epstein
Johns Hopkins Hospital
Baltimore, MD


Synovial sarcoma, spindle, biphasic