Cervical arachnoid cysts after craniocervical decompression for Chiari II malformations: report of three cases

We describe three cases in which ventrally situated cervical arachnoid cysts led to spinal cord or cervicomedullary compression after repeat craniocervical decompression for Chiari II malformations.

All three patients underwent craniocervical decompression when their Chiari malformations became symptomatic. The first patient developed chronic vertiginous spells and headache and was treated with repeated craniocervical decompression procedures during several years. Seven months after undergoing her third decompression procedure, she developed severe dizzy spells, which were determined to be of brain stem origin. The second patient had a small, asymptomatic arachnoid cyst anterior to the brain stem discovered at age 6 years. After undergoing repeat craniocervical decompression for headaches 8 years after undergoing his first procedure, the patient developed severe neck pain and acute quadraparesis. A third patient underwent repeat craniocervical decompression at age 14 years for cranial nerve dysfunction. Postoperatively, he acutely developed paresis of extraocular movements and incoordination of the upper extremities. All three patients were found to have anteriorly situated arachnoid cysts compressing the brain stem and/or cervical spinal cord.

Fenestration of the arachnoid cyst or drainage with cystoperitoneal shunting adequately treated acute brain stem or cervical spinal cord compression. All three patients had achieved satisfactory relief from their acute symptoms of neural compression at their follow-up examinations.

An association between spinal arachnoid cysts and neural tube defects has previously been reported. However, the development of previously undetected spinal arachnoid cysts after craniocervical decompression was unexpected. We hypothesize that extensive craniocervical decompression may alter the cerebrospinal fluid pressure dynamics in such a way that the anterior subarachnoid space, previously compressed, may dilate. Occasionally, because of perimedullary arachnoiditis, the cerebrospinal fluid may become loculated and act as a mass. Direct fenestration or shunting may successfully treat this problem, and less extensive craniocervical decompression may avoid it.