Extradural spinal synovial cysts in nine dogs

Nine dogs presenting for investigation of cervical or thoracolumbar myelopa thies were diagnosed with extradural spinal synovial cysts. Degenerative di sease affecting the articular facets or intervertebral discs was present on plain spinal radiographs in all cases. Myelography was consistent with dor solateral, extradural spinal cord compression. Two groups of dogs were iden tified: (1) young, giant breed dogs with multiple cysts involving one or mo re levels of the cervical spinal cord; and (2) older, large breed dogs with solitary cysts involving the thoracolumbar spinal cord. The synovial cysts constituted the major compressive lesions in four of the dogs. Analysis of lumbar cerebrospinal fluid demonstrated albuminocytological dissociation, consistent with chronic compressive myelopathy, in six dogs. All dogs under went decompressive surgery and the diagnosis of synovial cysts was confirme d histologically. The mean follow-up period was 17 months (range four to 36 months). At the time of follow-up, all dogs were fully ambulatory with imp roved neurological function compared with that at initial presentation.