MALIGNANT CHROMATOPHOROMA IN A CANEBRAKE RATTLESNAKE (CROTALUS-HORRIDUS-ATRICAUDATUS)

An adult female canebrake rattlesnake (Crotalus horridus atricaudatus) at Zoo Atlanta (Atlanta, Georgia, USA) had a subcutaneous mass on the left lateral abdomen. Microscopically, the tumor contained a pleomorp hic population of cells with abundant intracytoplasmic brown to gold n onrefractile pigment (chromatophores), large stellate cells resembling neurons, and small stellate cells whose cytoplasmic processes formed a fibrillar matrix. The pigment stained black with the Fontana-Masson technique and was positive with the periodic acid-Schiff technique (pr ior to and after diastase treatment). Neuron-specific enolase was dete cted in the large stellate cells using an immunohistochemical staining technique. In addition, glial fibrillary acidic and S-100 proteins we re detected in the chromatophores with immunohistochemical staining. T he smaller stellate cells were strongly S-100 positive. Ultrastructura lly, chromatophores contained intracytoplasmic structures composed of concentric lamellar membranes bordered by a triple-layer outer membran e. The morphology of these structures was compatible with pterinosomes . Three fluorescent pigments were isolated from the neoplasm by one-di mensional chromatography and characterized by spectrophotometry and sp ectrofluorometry.