Extraforaminal Lumbar Synovial Cyst Causing Sudden Foot Drop

A 52-year-old female presented with extraforaminal lumbar synovial cyst at the L4-5 level causing sudden foot drop on the right. Computed tomography, magnetic resonance (MR) imaging, and coronal MR myelography source images identified the cystic mass in the extraforaminal zone. The patient underwent microdecompression via a lateral transmuscular route, and the extraforaminal cyst compressing L4 ganglion was successfully removed. The histological diagnosis was synovial cyst. This unique case of surgically proven extraforaminal lumbar synovial cyst causing sudden foot drop indicates that extraforaminal synovial cyst should be included in the differential diagnosis of patients presenting with sudden foot drop.