Objective: There is currently no consensus regarding surgical indications for symptomatic sacral perineural cysts.

Methods: 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.

Results: 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 24 hours 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).

Conclusions: 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.