Intraparenchymal Occipital Cyst Formation after Contralateral Dural Arteriovenous Fistula Obliteration: A Case Report.

Postoperative intracranial cyst formation is a rare complication. We report a case of an air-containing cyst in the contralateral left occipital lobe parenchyma after ligation of a dural arteriovenous fistula of the right transverse sinus. We reviewed related literature and discussed the mechanisms of this rare complication. A 59-year-old man presented with a right transverse sinus dural arteriovenous fistula with cortical reflux discovered incidentally during a brain checkup. The patient underwent surgical ligation of the draining vein combined with spinal drainage for intraoperative brain relaxation and to minimize retraction. The next day, there were no complications, and the subcutaneous drain was removed. Two days after surgery, right lower-quarter blindness appeared, and computed tomography showed the formation of a cyst in the contralateral left occipital lobe containing blood mixed with the cerebrospinal fluid and air. The fluid and air that accumulated in the epidural space and subcutaneously could have been drawn into the brain parenchyma through the dural tear on the surface of the left occipital lobe via the check valve mechanism and "reverse soda bottle effect," resulting in cyst formation. The described complication appears to result from a coincidental combination of factors such as inadequate dural closure, unrecognized dural injury, and spinal drainage. Cyst formation after simple craniotomy is rare, but it can cause serious sequelae. For prevention, it is essential to understand its mechanisms and take appropriate measures.