Thoracic intramedullary arachnoid cyst in an infant.

Symptomatic intramedullary arachnoid cysts are rare, especially in children; these lesions are rarely described as a cause of spinal cord compression in this age group. The authors report on an 18-month-old boy who experienced a sudden loss of his ability to stand and walk due to a paraparesis. Magnetic resonance imaging of the spine exhibited a cystic intramedullary lesion at the level of T5-6. A hemilaminectomy was performed, and after myelotomy the cystic lesion was decompressed by fenestration to the subarachnoid space. The histopathological examination verified the diagnosis of an arachnoid cyst. In the postoperative course the boy experienced complete resolution of the initial paraparesis.