Answer: Low grade leiomyosarcoma

Histology: The lesion consists of fasicles of spindle cells with abundant eosinophilic cytoplasm. The nuclei are elongated and cigar shaped. Many of the nuclei appear relatively uniform without significant pleomorphism. Other areas show more striking nuclear pleomorphism. Mitotic figures are rare with no evidence of necrosis. The lesion is of moderate cellularity.

Discussion: In an adult, the most common paratesticular soft tissue tumor is liposarcoma, typically well differentiated. Paratesticular leiomyosarcomas are less frequently present. Although adenomatoid tumors of the testis may show a very prominent smooth muscle component one still will be able to identify the epithelial component of an adenomatoid tumor which is lacking in the current case. Also the presence of atypia in the current case rules out leiomyoma and smooth muscle hyperplasia with an adenomatoid tumor. Although there is striking cytologic atypia, the overall cellularity is not high, mitotic figures are not frequent, and the lesion lacks necrosis such that it would be best regarded as low grade leiomyosarcoma. In a study from our institution, the key prognostic feature is the grade of the tumor. All patients with low grade leiomyosarcomas were alive without evidence of disease although a couple of patients experienced local recurrences. In contrast all of the high grade leiomyosarcomas were dead of disease. Therapy typically consists of radical orchiectomy. Immunohistochemically these lesions express muscle markers as in other sites. The only pitfall that one must be aware of is as with leiomyosarcomas elsewhere, some of these lesions may show focal expression for cytokeratin.