Post-operative spinal subdural extra-arachnoid hygroma causing cauda equina compression: a report of two cases.

We present two cases of symptomatic, post-lumbar surgery cauda equina compression due to formation of a dissecting subdural extra-arachnoid cerebrospinal fluid (CSF) collection (hygroma) under tension. In both cases, a small inadvertent durotomy was sustained during the initial surgery. Surgical re-exploration confirmed a tension subdural extra-arachnoid hygroma due to one-way flow of CSF through a pinhole puncture in the arachnoid. The mechanism and clinico-radiological features of this rare post-operative complication are discussed.