Migrating lumbar facet joint cysts

Synovial cyst mimicking an intraspinal sacral mass

A 68-year-old female had a three-week history of severe low back pain radiating down the posterior left buttocks and left leg exacerbated by standing and walking. Lumbar spine MRI revealed cystic mass with similar intensity to cerebrospinal fluid located on dorsolateral left side of the sacral spinal canal inferior to the S1 pedicle. There was compression of left exiting S1 and traversing S2 nerve roots. Neurosurgery consult was requested to evaluate the cystic mass in the sacral spinal canal. After clinical evaluation, an unusually located synovial cyst was thought possible. Cyst contents were heterogeneous, suggestive of small hemorrhage and acute clinical history seemed reasonable. Left S1 and partial left S2 hemilaminectomy was performed and an epidural, partially hemorrhagic cyst was removed. There was no obvious connection to the ipsilateral L5-S1 facet joint. Pathology revealed synovial cyst, and the patient's leg pain was improved postoperatively. This synovial cyst was unusual as it had no connection with the facet joint intraoperatively and its location in the sacral canal was uncommon.

Evidence that atypical juxtafacet cysts are joint derived

OBJECT

Juxtafacet cysts (JFCs) in usual locations have recently been shown to have joint connections. The pathogenesis of JFCs in unusual locations has remained obscure. The authors hypothesize that all JFCs, including atypical ones, are joint derived.

METHODS

In this study the authors sought to explain the occurrence and formation of clinical outliers of spinal JFCs. In Part I, they performed an extensive literature search to identify case reports of spinal intraneural cysts that have been unappreciated despite the fact that they should occur. In Part II, they studied far-lateral (extraforaminal) cysts treated at their institution and reported in the literature. The presence of a joint connection was specifically looked for since this finding has not been widely appreciated.

RESULTS

In Part I, 3 isolated case reports of spinal intraneural JFCs without reported joint connections were identified: 2 involving L-5 and 1, C-8. In Part II, 6 cases involving patients with far-lateral JFCs treated at the authors' institution were reviewed and all 6 had joint connections. Two of these cases had been previously published, although their joint connections were not appreciated. In 2 of the newly reported cases, arthrography confirmed a communication between the facet and the cyst. Only 1 of 5 cases in the literature had a recognized joint connection.

CONCLUSIONS

The authors believe that all JFCs are joint derived. This explanation for intraneural and extraneural JFCs in typical locations would be consistent with the unified articular (synovial) theory and the pathogenesis for intraneural and extraneural ganglion cyst formation in the limbs. Facet joints appear no different from other synovial joints occurring elsewhere. Understanding the pathogenesis of these cysts will help target treatment to the joint, improve surgical outcomes, and decrease recurrences.