Acute cauda equina syndrome secondary to a lumbar synovial cyst

Cauda equina syndrome is a well described state of neurologic compromise due to lumbosacral root compression. In most cases, it is due to a herniated disc, tumor, infection, or hematoma. We report a case of rapid lumbar synovial cyst expansion leading to acute cauda equina syndrome and compare it to similar cases in the literature. The patient is a 49-year-old woman with a history of chronic low back pain who developed cauda equina syndrome. Serial lumbar magnetic resonance imaging studies demonstrated a significant increase in the size of a lumbar synovial cyst over a 2 week interval. After an unsuccessful attempt to relieve her acute symptoms with computed tomography-guided cyst aspiration, an L4-5 posterior spinal decompression with excision of the synovial cyst was performed. Postoperatively the patient's perineal numbness, bladder incontinence, and associated pain complaints resolved. The only residual symptom at one month follow-up was continued numbness in the right lower limb in an L5 distribution. This report adds to 6 other well described similar cases found in the literature by illustrating several important points. First, a lumbar synovial cyst is a rare but possible cause of acute cauda equina syndrome. Second, magnetic resonance imaging is the test of choice to diagnose and characterize lumbar synovial cysts; serial imaging can detect fluctuations in cyst size. Third, percutaneous treatment of lumbar synovial cysts is variable in efficacy and proved to be unsuccessful in our patient. Finally, surgical management has shown high success rates for symptomatic cysts. Specifically, in the setting of acute cauda equina syndrome secondary to a lumbar synovial cyst, urgent surgical decompression has led to resolution of neurologic symptoms in most reported cases. A lumbar synovial cyst is an uncommon cause of acute cauda equina syndrome. Prompt diagnosis and treatment may lead to reduced morbidity associated with this condition.