Kyste synovial postérieur lombaire

The lumbar synovial cyst is a periarticular cystic developing from the posterior interapophyseal joints and representing a rare, non discal etiology of lower back pain and/or of sciatica of spinal origin. We report the case of a 50-year old woman who consulted with left L5 radiculopathy. Lumbar CT scan (A) showed, at the L4-L5 level, a well-limited round lesion of 15 mm with wall thickening next to the left degenerative posterior joint. Lumbosacral spine MRI (B and C) revealed a left-sided poster lateral synovial cyst at L4-L5 level. The cyst was excised en bloc and associated with a foraminotomy. The clinical course was favorable. Synovial cyst most commonly affects middle aged subjects. Its location is, in most cases, lumbar at L4-L5 level. MRI is the modality of choice in the diagnosis of synovial cysts showing the seat of the cyst, its communication with the facet joint and its signal which is variable depending on its content: fluid identical to cerebrospinal fluid or hyperintense on T2 and T1weighted images or with gaseous content (void area signal). Treatment is primarily medical and it is based on intra-articular corticosteroid injection during arthrography or under CT scan. Surgery is only indicated in cases of failure of medical treatment.