Keyhole aqueduct syndrome.

Communicating syringes confined to the brain stem are extraordinarily rare. Two patients, presenting with signs and symptoms of cerebellar dysfunction, later developed evidence of brain-stem disease with dysarthria, nystagmus, deafness, and internuclear ophthalmoplegia. The condition of both patients had been diagnosed clinically as multiple sclerosis, but at autopsy they had a striking keyhole-shaped syrinx in the midbrain and upper pons, which communicated with the aqueduct and fourth ventricle without associated syringomyelia. In addition, both patients had marked atrophy and gliosis of the cerebellum, one with extension of the syrinx into cerebellar folia. The unique character of these lesions coupled with the similarity of the clinical features of the cases prompted us to name this disorder--"keyhole aqueduct syndrome."