Lumbosciatica Indicative of an Intradural Lumbar Spinal Arachnoid Cyst

Introduction. Spinal arachnoid cysts (SAC) are uncommon lesions that result from a small defect in the arachnoid resulting in an intradural or extradural arachnoid hernia. Their diagnosis is misleading. Surgery is required when SAC is symptomatic. The modalities of this surgery are still the subject of controversy. We report an unusual case of intradural lumbar SAC. Observation. A 43-year-old man consulted for a right L5 lumbosciatica evolving for at least 7 years. Rheumatological examination noted lumbar spinal syndrome and radicular syndrome. The neurological examination was normal. Lumbar CT scan had shown discrete protrusive disc disease. Medical treatment had been prescribed. In view of the persistence of pain, magnetic resonance imaging (MRI) was prescribed. This was performed 6 months later when the patient had experienced a worsening type of cauda equina syndrome. This MRI had objectified signs in favor of an intradural lumbar SAC. The patient was transferred to neurosurgery. Cyst excision was performed and histology had confirmed the arachnoid nature of the cyst wall. The postoperative follow-up was simple and the patient had to recover completely from his neurological deficits. Conclusion. The diagnosis of SAC can be misleading and late in the stage of significant neurological disorders. Do not hesitate to request an MRI for a rebellious lumbosciatica with a normal CT scan in a patient without neurological deficits.