Lumbar Radiculopathy Caused by an Undetected Facet Joint Cyst: A Case Report on Diagnostic Challenges and Endoscopic Treatment.

Abstract

Case report. To describe a rare case of lumbosciatalgia caused by a synovial facet joint cyst undetected on preoperative MRI, successfully diagnosed and treated with a minimally invasive endoscopic approach. Low back pain with sciatica (lumbosciatalgia) is a common and disabling condition. Facet joint cysts are uncommon but may cause nerve root compression and radiculopathy. Magnetic resonance imaging (MRI) is the diagnostic gold standard, but dynamic or small cysts may remain undetected, complicating diagnosis, and delaying appropriate treatment. A 46-year-old male presented with chronic lumbosciatalgia unresponsive to conservative management. MRI showed lumbar spondyloarthrosis, degenerative disc disease, and ligamentum flavum thickening, but no definitive cause of neural compression. Persistent symptoms and diagnostic uncertainty prompted minimally invasive endoscopic exploration. Intraoperatively, a synovial facet cyst measuring 1.1×1.0×0.2 cm was found compressing the descending L5 nerve root. The cyst was excised completely, resulting in immediate pain relief. Functional status, assessed using the Oswestry Disability Index (ODI), improved from 26% preoperatively (moderate disability) to 8% at 30 days (minimal disability), and further to 2% at 60 days, with stability maintained at 90, 150, and 180 days. No recurrence or complications were observed. This case highlights the importance of considering facet joint cysts in the differential diagnosis of lumbosciatalgia, especially when imaging is inconclusive. Minimally invasive endoscopic surgery enables both definitive diagnosis and treatment, offering minimal tissue disruption, rapid recovery, and sustained symptom resolution. Early suspicion, personalized surgical planning, and structured follow-up are key to optimizing outcomes and monitoring for recurrence.