Synovial cysts occur throughout the body and are generally benign lesions with limited clinical consequences. Juxtafacet
cysts of the spine, in contrast, often press on a nerve root as it exits in the foramen, causing
radiculopathy. Synovial tissue that emanates from the facet joint but extends medially, is an additional important cause of
spinal stenosis. Over the past 5 years, neurosurgeons at our institution have operated on a large number of patients with
back pain, with removal of abnormal synovial tissues. Histological examination of these tissues distinguishes the different types of
pathologic processes responsible for producing symptoms. Juxtafacet
cysts may be either
mucin-filled
ganglion cysts devoid of
cyst lining or true
synovial cysts with watery content and lined by synovial cells.
Ganglion cysts arise in degenerated ligament at the facet joint, and occasionally within synovial stroma.
Synovial cysts arise within synovium and, unlike
synovial cysts in the extremities, have a thick wall containing granulation tissue, numerous histiocytes and giant cells. This hyperplastic, irritated synovium of the spine, which we term "synovial excrescences", is voluminous and this reactive part overshadows the cystic portion of the lesion in most instances.
Iron pigment deposition and
inflammation are mild to absent, making synovial excrescences different from
pigmented villonodular synovitis. Synovial excrescences of the spine are an important cause of
spinal stenosis, predominantly in elderly patients. Surgical removal of excrescences protruding into the spinal canal provides prompt and durable relief of symptoms, usually without the need for extensive bony
laminectomy or
spinal fusion. Several patients in our study had both spinal ganglion
cysts and synovial excrescences, suggesting common risk factors for both lesions.