[Progressive paralysis of divergence in an adult with midbrain angioma]

A 37-year-old woman was admitted to the hospital with the complaint of progressive horizontal diplopia of six years' duration when viewing distant objects. On admission she had a slight left convergent strabismus. Homonymous diplopia was present beyond 50 cm and increased on distance fixation. Both eyes were fully mobile in the horizontal plane with a mild decrease in the velocity of horizontal eye movement to the left, and slight impairment of upward eye movement. The left eye did not fully adduct during convergence. The right pupil was slightly larger than the left. Prism cover test showed 6 delta esophoria at 30 cm and 14 delta esophoria at 5 m. The Hess chart showed a convergent deviation. MRI revealed a small right-side paramedian lesion of the midbrain tegmentum lying ventral to the aqueduct of Sylvius, at the level between the superior colliculi and the intercollicular area. A venous angioma with arteriovenous shunts in the right midbrain was diagnosed by angiography. We suggest that lesions that damage the divergence neurons in the tegmentum of the midbrain and also interrupt the supranuclear fibers having an inhibitory effect on the convergence neurons may produce homonymous diplopia on distant fixation combined with the esotropia.