Spinal schwannoma missed on lumbar MRI: a case report.

A 55-year-old male presented with 9 months of left buttock and lower limb pain, initially misdiagnosed as lumbar disk herniation. Unsuccessful lateral recess block and physical therapy prompted further evaluation. Lumbar magnetic resonance imaging (MRI) revealed a right L5 nerve root cyst, yet symptoms worsened. Examination showed left paraspinal tenderness, grade IV left lower limb weakness, hyperesthesia, and positive straight leg raise tests. Selective nerve root block localized the lesion to the left L5 root; contrast-enhanced MRI identified an L4-5 facet joint cyst with inflammation. Arthroscopic-assisted Uni-portal Spinal Surgery (AUSS) endoscopic resection under general anesthesia was performed, with pathology confirming schwannoma. Postoperatively, pain intensity (numerical rating scale, NRS) decreased from 7 to 2 within 24 h; discharge occurred on day 6. At 2-month follow-up, symptoms resolved completely. This case underscores the diagnostic pitfalls of lumbar schwannoma (mimicking disk herniation/cysts) and highlights the roles of nerve root blocks, contrast MRI, and histopathology. AUSS endoscopy achieved definitive management.