Tumore misto maligno dello stroma gonadico in uno stallone

A 30 year old Standardbred stallion was examined for an unilateral scrotal swelling. Physical and ultrasound examinations revealed a painless enlarged left testis with a non-homogeneous echogenicity, as compared to the controlateral testis. The stallion underwent left unilateral ochidectomy. Grossly, the excised testis was irregularly enlarged (12x9x9 cm; weight: 530 g) and form. On the sections, testicular parenchyma was replaced by a lobulated, grey-white mass, which involved the epididymal head. At microscopy, a double Leydig and Sertoli cell tumour component could be seen. In the latter, that prevailedm frequent pleomorphic cells and mitotic figures were observed, with occasional vascular invasion. Tumour patterns showed tubular or solid areas, cord-like or diffuse in apperance, among which newly-formed Leydig nests and low-density fibrillar bundles were interposed. Immunohistochemically, a weak/moderate immunostaining for vimentin, AE1/AE3 cytocheratin, alfa-1-antitrypsin and CD99 antigens was found, in the growing Sertoli cells, whose nuclear MIB-1 labeling index was scored 13+/-2 (%). The Leydig tumour cells displayed, in their turn, a moderate/strong positivity for alfa-inhibin, vimentin, cytocherratin, neuron specific enolase and CD99. On these bases, a diagnosis of malignant mixed dex xord-stromal tumour was made.