Myelographic CT, A Check-Valve Mechanism, and Microsurgical Treatment of Sacral Perineural Tarlov Cysts

Abstract

There is currently no consensus regarding surgical indications for symptomatic sacral perineural cysts. Nine patients with symptomatic sacral perineural cysts underwent microsurgery. All patients fulfilled the following criteria: (1) cyst sizes larger than 15 mm; (2)cysts show the "delayed inflow" and/or "delayed outflow" of contrast on myelographic computed tomography (CT), and (3)neurological symptoms correlate with the primary cyst. On myelographic CT, all primary cysts showed the "delayed inflow" of contrast; the average cyst/thecal sac Hounsfield units (HU) ratio was 0.17. In 7 patients, the primary cyst showed "delayed outflow"; the average cyst/thecal sac HU ratio increased to 3.12 on images obtained 24hours after contrast injection. Regarding the modified Rankin Scale, 67% of patients reported that their overall symptoms improved to normal activities after surgery. The most improved symptom was coccydynia (75% improvement, P= 0.017), followed by leg radiation pain (67% improvement, P= 0.027) and buttock pain (50% improvement, P= 0.068). Bowel/bladder dysfunction improved in 100% of patients, but newly developed in 1 patient (P= 0.32). Perineal pain only decreased in 33% (P= 0.41). To the best of our knowledge, this is the first study to have performed a quantitative analysis of the dynamics of cerebrospinal fluid in sacral perineural cysts using myelographic CT. Sixty-seven percent of patients benefited from surgery; however, our criteria may not be a necessary and sufficient condition for patient selection because 33% did not respond to surgery despite the successful elimination of the check-valve.