The Acetazolamide Challenge: A Tool for Surgical Decision Making and Predicting Surgical Outcome in Patients with Arachnoid Cysts.

Background and Study Aims  Arachnoid cysts (ACs) are benign congenital malformations of the arachnoid that may present with either localizing or nonspecific symptoms. ACs with mass effect are detected frequently in asymptomatic patients. Conversely, symptomatic patients may present without imaging signs of a focal mass effect that emphasizes the difficulty of relying on imaging as the sole criteria in surgical selection. We hypothesize that symptomatic AC may be related to the elevated fluid pressure within the cyst on surrounding structures. Thus reducing the amount of fluid in the cyst or surrounding cerebrospinal fluid (CSF) by using acetazolamide (AZM), a carbonic anhydrase inhibitor known to reduce CSF production, might mimic surgical decompression and therefore could serve as a decision-making tool in patients with ACs. Methods and Patients  A total of 103 patients with radiographically proven ACs were initially identified. Twenty (19.4%) were symptomatic and underwent a trial of oral AZM. Data were collected meeting inclusion/exclusion criteria for this cohort study and analyzed retrospectively/prospectively. Results  Overall, 17 patients were able to tolerate the AZM and had at least some subjective improvement in their symptoms during the AZM challenge and underwent surgical therapy. Surgery was beneficial in 16 patients (94.1%). Following surgery, symptoms resolved in 13 patients (76.5%) and improved in 3 (17.6%). Conclusion  The AZM challenge may support the clinical decision to recommend surgery in those patients whose symptoms improve during AZM therapy.