Spinal extradural meningeal cyst with spinal stenosis.

Study Design: Case report.
Objective: To present a rare pathology causing a common disease.
Setting: Spine unit of the orthopaedic surgery department of a university hospital in Berlin/Germany.
Case Report: A 39-year-old female with an intraspinal extradural arachnoid cyst of the lumbar spine presented with intermittent radiating lumbar pain. The magnetic resonance imaging (MRI) showed a dorsal spinal extradural arachnoid cyst at L3/4. After wide laminotomy L3, operative cyst resection and stabilisation at L3/4 by posterior lumbar interbody fusion (PLIF), major symptom relief occurred.
Conclusion: Spinal extradural arachnoid cysts are a rare entity causing low back pain and intermittent radicular syndromes. They can be caused by arachnoid herniation through dural weak spots which are hereditary or occur after trauma. A ball-valve mechanism promotes growth. The main diagnostic tool for spinal extradural cysts is the MRI scan. Additionally, myelography is helpful to demonstrate fluid communication. Complete surgical removal of the cyst should be attempted to reduce risk of recurrence. If extensive decompression is needed for the surgical approach causing segmental instability, interbody fusion is recommended. The outcome depends on age, duration and degree of neurological damage.