Three German Shepherd Dogs that were presented for investigation of chronic unilateral hindlimb lameness and pain in the lumbosacral region were diagnosed with an intraspinal, extradural synovial cyst and reactive fibrosis protruding into the foramen of the lumbosacral articulation using magnetic resonance imaging and histology. This extradural mass compressed the nerve root in the foramen and the cauda equina. During a dorsal laminectomy and unilateral partial foraminotomy, the cyst and the fibrotic tissue were removed with the aid of a 2.4 mm 30° arthroscope for visualization of the foramen. The fibrotic tissue surrounding the cysts was in all cases confluent with the annulus of the intervertebral disc. The histological examination confirmed the diagnosis of a synovial cyst in all three cases by finding inflamed synovial membrane in the samples from the wall of the cyst as well as reactive fibrosis and cartilaginous metaplasia in the surrounding tissue. The three patients improved after the surgery and were pain free during the follow-up evaluations.
Keywords: Synovial cyst; dog; foraminal stenosis; lameness; lumbosacral.