Malignant Peripheral Nerve Sheath Tumor in a Water Moccasin (Agkistrodon Piscivorus)

Abstract

Peripheral nerve sheath tumors (PNSTs) in domestic and wild animals are uncommon tumors that originate from cells that comprise the sheaths of peripheral nerves. One type of PNST originates from Schwann cells and is termed schwannoma. Two other types of cells, perineural cells and fibroblasts, are components of peripheral nerve sheaths and may give rise to tumors. These tumors, particularly the malignant variety, may have histologic patterns that closely mimic those of other fusiform tumors. Electron microscopic and/or immunohistochemical evaluation is often necessary to establish a diagnosis of PNST. 11,13 PNSTs affecting cranial or spinal nerve roots and the brachial plexus have been described in several animal species (cattle, dog, cat, rat). 11 Malignant cranial and spinal PNSTs are rare in animals and metastasize infrequently. 3,11 In this report, a malignant PNST originating from a spinal nerve with hepatic and splenic metastasis is described in a snake.A 12-year-old captive-bred male water moccasin (Agkistrodon piscivorus) developed a firm nonulcerated and progressive swelling of the subcutaneous tissue on the right midbody. Flaccid paralysis and lack of propriocepcion was present distal to the lesion. The head and neck were displaced laterally to the left. The snake was anesthetized using a face mask with isofluorane a in oxygen for induction followed by tracheal intubation. A biopsy of the costal mass was obtained for evaluation. The histopathologic diagnosis was invasive undifferentiated spindle cell sarcoma. Neoplastic cells were observed in all the sample edges. The animal was again anesthetized to completely resect the cutaneous mass. The previous diagnosis was histologically confirmed, and neoplastic cells were observed in the deeper resection border associated with the ribs.Three months later, a new and larger subcutaneous swelling was observed in the same location. The snake's general condition had markedly worsened: it was anorectic and the head displacement, flaccid paralysis, and lack of propriocepcion were more pronounced. The animal was again anesthetized and positioned in sternal recumbency to evaluate the extension of the new lesion and to detect possible metastasis by radiography and magnetic resonance imaging (MRI). Plain radiographs revealed a large, poorly defined soft tissue mass on the right costal wall that invaded the celomic cavity. On MRI, transverse sections revealed a hyperintense mass on the right side of the body. The mass was located in the paravertebral muscles and invaded the celomic cavity through the intercostal spaces. It also invaded the vertebral canal through intervertebral foramina and compressed the spinal cord (Fig. 1). Coronal sections demonstrated neoplasFrom the Department of Pathology (Ramis, Pumarola, Majó) and the Veterinary Teaching

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