Iatrogenic Spinal Subdural Extra-Arachnoid Hygroma Following Uncomplicated Lumbar Decompression.

Intradural spinal arachnoid cysts (ISACs) have been reported in the current literature as either an idiopathic disease or exceedingly rare sequelae after lumbar puncture, spinal trauma, or meningitis. Other studies have more appropriately termed the iatrogenic pathology as a spinal subdural extra-arachnoid hygroma (SSEH), as there is not often a clear cyst wall as in a true arachnoid cyst. However, to the best of our knowledge, none of the previous studies described an SSEH following uncomplicated posterior lumbar surgery, as they have previously involved clear durotomies during the initial operation. Here, we report the case of a 53-year-old woman who presented to the emergency department with a persistent severe orthostatic headache and worsening leg pain, six days following an uneventful L5-S1 discectomy and left L4-5 laminoforaminotomy, without intraoperative durotomy. Lumbar magnetic resonance imaging (MRI) scan revealed a pseudomeningocele and an SSEH extending from the S1 up to the lower thoracic spine, compressing and displacing the cauda equina. Although the hygroma extended up to the lower thoracic spine, surgical exploration was performed only at the index surgical site with bilateral L5 laminectomy, wide durotomy, and wide fenestration of the arachnoid layer. Postoperatively, her headaches dissipated and her pain improved with complete radiographic resolution of the collection. Iatrogenic SSEH is an exceedingly rare complication of posterior lumbar decompression and can occur in the absence of a durotomy during the index surgery. Although these hygromas may span multiple levels, the initial surgical site or the site of known durotomy should be explored first. They can potentially be treated with only a limited durotomy and arachnoid fenestration at a single level rather than at a multilevel arachnoid fenestration.