Attending Physician Mayo Clinic Faribault, Minnesota, United States
Case Diagnosis: Postoperative adhesive arachnoiditis
Case Description: A 61-year-old female with remote history of bilateral L4 laminectomy presented with years-long, insidiously-starting low back pain that radiated into the left hip and laterally down the left leg to the left ankle. Her pain worsened with movement, particularly at night. She denied numbness, tingling, incontinence, or saddle anesthesia, but endorsed weakness of the left lower extremity, with recent falls. She had previously tried physical therapy, Gabapentin, spinal cord stimulator implantation, left L5/S1 selective nerve root blocks, and an ultrasound-guided left piriformis tendon sheath injection, all without long-term improvement of her symptoms. Physical exam was non-contributory. Lumbar spine MRI showed displaced nerve roots of the cauda equina below L3 to the periphery of and adhering to the dural sac, an “empty sac sign,” indicative of adhesive arachnoiditis. Her persistent pain was caused by postoperative adhesive arachnoiditis, occurring from her prior L4 laminectomy, which effectively impinged on several nerve roots.
Discussions: Arachnoiditis is a painful condition associated with inflammation of the arachnoid mater, one of the meningeal layers that surround the spinal cord. The most common precipitating factors of arachnoiditis include infection, intracranial or intraspinal hemorrhage, herniated discs, and intrathecal medications or contrast. Spinal surgery may also be a risk factor for adhesive arachnoiditis, but it is typically associated with disc-related surgeries and arachnoiditis is often only incidentally found on later imaging. Rarely does postoperative adhesive arachnoiditis result in persistent, unrelenting pain.
Conclusions: Postoperative adhesive arachnoiditis is usually a non-painful, often incidental, imaging finding, but rarely it can present as chronic low back pain when the adhesions impinge on the spinal nerve roots.