HISTORY

A 12 year-old, male mixed-breed dog presented with a 1-month history of chronic paraparesis. Physical examination was unremarkable. Neurologic examination showed non-ambulatory paraparesis, CP deficits in both pelvic limbs, worse on the left, and normal spinal reflexes. Pain was not detected on paraspinal palpation. Lesion localization was T3-L3. Main differential diagnoses included neoplasia, degenerative disease and infectious/inflammatory conditions. CBC and serum biochemical profile showed abnormalities consistent with chronic steroid administration. Thoracic radiographs and abdominal ultrasound were unremarkable. Plain spinal radiographs and myelography were performed under general anesthesia. The LL myelographic views showed thinning of the dorsal contrast column over T2-T4. On the VD views a marked deviation of the spinal cord to the right was observed at T3-T4. CT confirmed the presence of an extradural, soft tissue mass at T3-T4, on the left side of the vertebral canal, displacing the cord to the right and causing significant compression. A left hemilaminectomy was performed to decompress the cord. An extradural, whitish mass, ventrolateral to the spinal cord was visualized invading the third left thoracic spinal nerve and firmly attached to the cord. The mass was completely removed with the spinal nerve. Histopathologic exam revealed a dense proliferation of polygonal cells. Invasion and destruction of the spinal nerve were also seen. Special immunohistochemical staining was consistent with a granular cell tumor.

DISCUSSION

Granular cell tumors, sometimes also called myoblastomas, are rare neoplasms; the origin of the cell characterizing these tumors being under dispute. Early reports attributed these tumors to myoblastic cells but succeeding reports have variously suggested mesenchymal, fibroblastic or histiocytic derivations. More recently, it has been proposed that they arise from Schwann cells or an even more primitive neuroectodermal precursor. Granular cell tumours have been reported in humans, dogs, cats, horses, rats, mice and a cockatiel. These neoplasms are characteristically found in different locations according to the species involved. In dogs, these tumours are almost always benign; most occur in the oral cavity, but they have also been reported in unusual sites such as the brain, heart, and lymph nodes. However, no reports of granular cell tumors in the spine of dogs have been found in the literature. Granular cell tumors tend to be poorly circumscribed nodules that may be solitary or multiple. Under the microscope they consist of rounded or polygonal cells of uniform character with small, centrally placed vesicular nuclei and coarsely granular eosinophilic cytoplasm. Excluding malignant examples of the tumor, recurrence is rare, local surgical excision should be curative in nearly all cases.

The tumor described in this case report is a granular cell tumor arising from the third thoracic spinal nerve and compressing the spinal cord. Excision of the tumor resulted in resolution of myelopathic signs and a favorable outcome of the case.