Intradural Symptomatic Arachnoid Cyst Formation Following Non-Instrumented Lumbar Decompression

Purpose Intradural arachnoid cyst is a rare complication of lumbar puncture, post-trauma or post-intraoperative durotomies. We aim to estimate the incidence of early intradural arachnoid cyst radiologically in non-instrumented posterior lumbar decompression among symptomatic patients, and establish clinical correlation. Materials and methods Patients who underwent lumbar decompression without instrumentation at a tertiary spinal service between December 2014 and January 2018 were identified. When MRI scans were performed post-operatively within 14 days, imaging, medical and operative records were reviewed by two consultant neuroradiologists. Results 488 operations were included. 46 operations were followed by an early MRI scan. 59% were requested to investigate new or ongoing pain. Ten demonstrated an intradural arachnoid cyst - seven had no documented durotomy. Eight were primary operations, three were emergency operations. Statistically, we have not identified durotomy, primary-vs-revision surgery, and elective-vs-emergency surgery as risk factors. Two patients required revision operations, of these, one had a repeat post-operative scan, where the cyst resolved following further decompression at the index level, without intradural exploration. Conclusions Intradural arachnoid cyst may complicate posterior lumbar decompression. To our knowledge, this is the first study to assess its incidence as an early post-operative radiological finding, which is likely to be commoner than we recognise. It may be a cause of persisting post-operative pain.