Excisão cirúrgica de um osteocondroma de raiz nervosa da cauda equina de cão

Background: Spinal neoplasms are classified into extradural, intradural/extramedullary or intramedullary. Intradural/extramedullary tumors include meningiomas and nerve sheath tumors, which arise from meninges or peripheral nerves around the spinal cord. Clinical signs are related to dysfunction of the involved nerve and include pain, nerve root signature and atrophy. Osteochondromas are benign tumors located within the bone, on its surface or in extra-osseous regions, when they are classified as soft tissue osteochondoma. The aim of this study is to describe a case of an osteochondroma in a nervous root of the cauda equina in a dog, whose surgical resection allowed the resolution of the clinical signs.Case: A 12-year-old, male, Labrador Retriever dog, was presented with a 40-day history of progressive, painful, pelvic limb paresis, with no improvement when treated with analgesics and acupuncture. Neurological abnormalities included paraparesis, sometimes worse in the left pelvic limb, that was carried flexed at the level of the stifle, hindlimb atrophy, decreased interdigital reflexes and pain in the lumbar spinal region, mainly over L6 vertebra. Results of blood count and serum biochemical analysis were unremarkable. Computed tomography (CT) of the lumbosacral area was performed and the evaluation of images in transverse and reconstructed dorsal and sagittal planes allowed the visualization of a hyperattenuating and calcified round structure with 8 mm x 6 mm, in the left side of vertebral canal, at the level of caudal epiphysis of L6. Lumbosacral (L7-S1) CT abnormalities, as subchondral sclerosis, mild disc margin bulging, spondylosis deformans and foraminal proliferation were also observed but were considered clinically insignificant. Then, a dorsal L6 laminectomy was performed and after opening of the vertebral canal it was observed the presence of an ovoid mass, in the left side of the medullary cone, measuring approximately 0.9 cm in length, originating from a sacral nerve root. This structure was excised and submitted to histopathological evaluation. The dog improved after surgery without any complications, and neurological functions were gradually recovered. The histopathology of the mass was confirmed as an osteochondroma.Discussion: The history and neurologic examination findings as well the improvement after surgery were compatible with the lesion visualized by TC in L6, rather than the degenerative changes in L7-S1. Regarding the position of the mass, the main differential would be nerve sheath tumor, one of the most common types of primary neoplasia of the peripheral nervous system, however in a CT study in dogs with brachial plexus and nerve roots neoplasms, calcification of the tumor was not observed. Most of benign cartilaginous tumors of soft tissue are chondromas/osteochondromas, and this lesion should not be confused with multiple osteochondroma or multiple cartilaginous exostoses, which have been reported as multifocal, proliferative lesions involving the surface of ribs, vertebrae and pelvis of young dogs. If this lesion is unique, it is called osteochondroma. There are two reports of chondromas into the first lumbar vertebrae of dogs, with adherence to the floor of the vertebral canal and one report of an osteochondroma originated from the left pedicle of T11 in a cat. Radiculopathy and myelopathy caused by osteochondromas inside the spine are rare in humans and description of this tumor arising from nerve roots were not found in the veterinary literature. Probably the origin of the mass was metaplasia of the meninges surrounding the nervous root. In conclusion, neurological examination, CT and surgical exploration allowed the diagnosis and removal of a soft tissue osteochondroma, a rare benign tumor, with good patient recovery.