ABSTRACT
Spinal extradural arachnoid cysts are unusual causes of symptomatic spinal cord compression. They represent expanding diverticula of the subarachnoid space herniating through a dural defect into the extradural space. The pathogenesis of this entity is still unclear. We describe the clinical, neuroradiological and surgical aspects of two young patients in whom symptoms attributable to thoracic spine compression were caused by spinal extradural arachnoid cysts. The first child presented with progressive spastic paraparesis accompanied by urinary incontinence, superficial and deep sensory disturbance below the umbilical level. The second patient presented with unstable gait as a result of weakness and diminished sensation in the lower extremities. Magnetic resonance imaging showed a thoracic posterior extradural arachnoid cyst in both patients. The cyst was completely removed by posterior approach. Histological examination confirmed the diagnosis of arachnoid cyst. Neurological symptoms progressively resolved after surgical decompression. Although quite rare, the diagnosis of arachnoid cyst should be included in the differential diagnosis of intraspinal extradural cystic lesions, causing spinal cord compression. Surgery is the treatment of choice, providing good clinical outcome