Extraforaminal facet synovial cyst causing radiculopathy in a 77-year-old patient: a case report on a rare condition with a review of the literature

Extraforaminal facet synovial cysts are rare lesions that can cause lumbar radiculopathy but are often difficult to diagnose due to their atypical location. A 77-year-old woman presented with a one-year history of severe left leg pain that significantly limited her mobility. Magnetic resonance imaging (MRI) revealed a cystic mass in the left L5/S1 extraforaminal region without communication to the facet joint, and magnetic resonance (MR) neurography demonstrated compression of the left L5 exiting nerve root. As conservative therapy failed, surgical excision was performed via total facetectomy followed by transforaminal lumbar interbody fusion to maintain stability. Intraoperatively, the cyst compressed the L5 nerve root and contained clear, gelatinous fluid. Histopathology confirmed a facet synovial cyst. Postoperatively, the patient achieved substantial pain relief and recovered independent ambulation. This case underscores the importance of considering extraspinal facet synovial cysts in patients with extraforaminal radiculopathy. MRI and MR neurography are invaluable for accurate localization and characterization, while surgical excision provides definitive treatment when conservative measures are ineffective. Early recognition and appropriate management lead to excellent clinical outcomes.