Rhabdomyosarcoma in a Texas Gopher Tortoise ( <i>Gopherus berlandieri</i> ). Case Report

Rhabdomyosarcomas are rarely reported in reptiles, and this is, to the authors′ knowledge, the second one described in a tortoise. A male captive terrestrial tortoise of at least 11 years of age ( Gopherus berlandieri ) was presented with a reddened growth of the distal aspect of the right posterior limb, measuring approximately 4.5 cm. The affected limb was amputated, and radiologic evaluation of the sample revealed osteolysis of the phalanges and peripheral inflammation. Initial histopathologic examination showed a nonencapsulated, high cellularity neoplastic lesion conformed by poorly differentiated cells with unappreciable or scant cytoplasm and a nucleus with one or two prominent nucleoli. Occasionally, bigger, eosinophilic, strap cells with evident cross‐striations were present and stained red by Masson′s trichrome stain. The tissue resulted negative for immunohistochemistry staining with MyoD1 and myogenin markers, yet transmission electron microscopy showed electron‐dense bands compatible with Z‐band remains which constitutes a high certainty criterion for the diagnosis of rhabdomyosarcomas. This case highlights the advantages of ultrastructural studies over the more commonly performed immunohistochemistry studies in the diagnosis of neoplasia in nondomestic animals.