Interdural spinal cyst following lumbar puncture: illustrative case.

backgroundInterdural spinal cysts are rare lesions located between the layers of the dura mater, not included in traditional spinal cyst classifications. Only 12 cases have been reported in the literature, with two located in the lumbar region. This case represents the first reported lumbar interdural cyst developing as a direct complication of a single lumbar puncture. OBSERVATIONS: A 44-year-old woman developed severe radicular pain 1 week after undergoing a diagnostic lumbar puncture; the pain was posture dependent, worsening when upright and improving when recumbent. MRI revealed a cystic lesion at L3-4 without nerve root compression. CT myelography showed delayed contrast filling, indicating communication with the subarachnoid space. Surgical exploration confirmed an interdural cyst. Both dural layers were sutured to obliterate the cyst and the defect of the inner dural layer. Her radicular pain resolved postoperatively. LESSONS: Interdural spinal cysts can form as a rare complication of lumbar puncture, causing persistent spinal pain. Such cysts should be considered in patients with unexplained, posture-dependent pain after lumbar puncture, as their dynamic nature may elude standard imaging. Suturing both dural layers to obliterate the cyst and repair the defect of the inner dural layer can effectively resolve the symptoms. https://thejns.org/doi/10.3171/CASE2652.