Idiopathic thoracic intradural and extradural arachnoid diverticula. Report of a case.

Intraspinal arachnoid diverticula are unusual lesions that may demonstrate significant mass effects. A 15-year-old boy with upper lumbar discomfort and progressive spastic paraparesis also demonstrated a sensory deficit at T-10 as well as a severe lower extremity dorsal column deficit. Radiographic evaluation demonstrated interpedicular widening from T-2 to T-9. Myelography revealed a triloculated arachnoid diverticulum, with major collections at C-7 to T-2, T-3 to T-5, and T-8 to T-10. An eight-level laminotomy (T-2 to T-9) was performed, leaving the spinous processes and interspinous ligaments intact. The inferior collection was completely extradural, with a diverticular neck leaving the right nerve root sleeve at T-8. The other loculations were intradural. The lesion was excised without difficulty, and the laminae were replaced. The postoperative course was unremarkable, in that recovery occurred almost immediately, and the patient's strength was essentially normal on discharge. In treating such lesions, replacement laminotomy is the best approach.