Disappearance of Arachnoid Cyst after Burrhole Trephination: Case Series.

We report 3 cases of arachnoid cysts (ACs) that completely disappeared after burr hole drainage, without cyst fenestration into the subarachnoid space or cystoperitoneal shunt. The first patient was a 21-year-old female with an AC of the right cerebral convexity, found incidentally. After endoscopic AC fenestration was performed, the patient complained of persistent headache. Two-month postoperative brain imaging revealed reaccumulated AC and associated multi-stage subdural hematoma. Burr hole drainage was performed to resolve the chronic subdural hematoma (CSDH). Three months later, brain computed tomography showed that the CSDH and the AC had disappeared. The second patient was an 11-year-old male who had a history of trauma 1 month prior to presentation at the clinic. Brain magnetic resonance imaging revealed an AC in the left sylvian fissure with CSDH. We performed burr hole drainage to treat the CSDH first. Subsequently, the AC as well as the CSDH disappeared. The third case was an AC of the right parietal convexity, found incidentally. Only burr hole drainage was performed, following which, the AC disappeared. This case series shows that an AC can disappear naturally after rupture into the subdural space by trauma or the burr hole procedure.