Background: Idiopathic arachnoid cysts are rare lesions not associated with trauma or other inflammatory insults. To date, there have been few large series describing the presentation and management of these lesions.
Methods: Twenty-one cases of intradural spinal arachnoid cysts were identified (1994-2001). Pediatric patients and cases with antecedent trauma were excluded. There were eight women and 13 men with an average age of 52 years. Follow-up averaged 17 months.
Results: Cysts were most commonly found in the thoracic spine (81%). Fifteen cysts were dorsal to the spinal cord and six were ventral to the spinal cord. All patients underwent laminectomy with cyst fenestration and radical cyst wall resection. Based upon intraoperative ultrasonography, four cysts were also shunted to the subarachnoid space, and seven patients had an expansile duraplasty with freeze-dried dural allograft. Of the seven patients with syringomyelia, three resolved with extramedullary cyst resection alone. Four required syrinx to subarachnoid shunting. Follow-up MRI demonstrated cyst resolution in all cases. All seven intramedullary syrinxes were decreased in size and four resolved completely. Weakness (100%), hyperreflexia (91%), and incontinence (80%) were more likely to improve than neuropathic pain (44%) and numbness (33%). One patient had increased numbness postoperatively.
Conclusions: Ventral cysts are more likely to cause weakness and myelopathic signs. Preoperative symptoms of neuropathic pain and numbness are less likely to improve than weakness and myelopathy. Utilizing intraoperative ultrasound to guide aggressive surgical treatment with the adjuncts of shunting and duraplasty results in a high rate of cyst and syrinx obliteration.