Enhanced Diagnosis and Management of Far‐Out Syndrome Using 3D Visualization and Uni‐Portal Non‐Coaxial Spinal Endoscopic Surgery: A Case Report With Literature Review

BACKGROUND: Far-out syndrome (FOS) is an uncommon cause of L5 radiculopathy that may be missed when extraforaminal compression lies beyond routine imaging planes. This report describes the added value of three-dimensional (3D) CT/magnetic resonance neurography (MRN) fusion for diagnosing persistent symptoms after lumbar endoscopic surgery and planning revision decompression. CASE PRESENTATION: A 55-year-old woman had persistent right L5 radiculopathy after unilateral biportal endoscopic discectomy (UBED). CT/MRI suggested L5-S1 extraforaminal stenosis. Patient-specific 3D CT/MRN fusion showed the exiting L5 root compressed by the L5 transverse process, sacral ala, posterior osteophyte, disc protrusion, and ligaments, redirecting revision planning to the extraforaminal zone. Uni-portal non-coaxial spinal endoscopic surgery (UNSES) achieved targeted bony, ligamentous, and disc decompression without vascular, neural, or dural injury. From pre-revision values of VAS 7/10 for back pain and 7/10 for leg pain, ODI 54%, and JOA 5, scores improved at postoperative Day 1 to 3/10, 2/10, 22%, and 23, respectively. At 1, 3, and 6 months, back/leg VAS was 2/1, 1/0, and 1/0; ODI was 24%, 16%, and 8%; and JOA was 23, 25, and 27, respectively. CONCLUSIONS: In this patient, 3D CT/MRN fusion complemented conventional imaging by integrating bone, disc, and nerve anatomy and directly informing revision decompression. UNSES was feasible, with improvement maintained through 6 months. As a single case, these findings support clinical feasibility and educational value rather than general efficacy or safety.