A 72-year-old man consulted his primary care physician because of confusion and vision loss of recent onset. He had no history of hypertension or diabetes.
An MRI scan of the brain revealed a significant signal change on T2-weighted and fluid-attenuated inversion recovery (FLAIR) imaging in the left medial occipital lobe; this finding was consistent with profound ischemia and infarction (A). Similar signal changes, which pointed to the same diagnosis, were seen in the right inframedial cerebellar hemisphere (B). No intracranial hemorrhaging was found.
The patient subsequently underwent an eye examination to confirm any permanent visual field defect. Visual acuity was 20/20 in each eye. His slit-lamp and funduscopic examination results were unremarkable. His computerized visual field analysis showed a dense congruous right inferior homonymous quadrantopsia (C and D). Visual field examinations repeated 1 year later revealed that the defect had persisted.
Homonymous hemianopsias and quadrantopsias result from damage to the postchiasmal portion of the visual pathway. A congruous visual field defect is one in which both half-fields are symmetric or identical in size, shape, position, density, margins, and all other characteristics. The more congruity in the 2 fields of a homonymous hemianopsia or quadrantopsia, the more posterior in the postchiasmal portion of the visual pathway is the lesion producing it. Homonymous symmetric defects indicate a location in the occipital cortex.