Glucose utilization of visual cortex following extra-occipital interruptions of the visual pathways by tumor. A positron emission tomography study.

Overview

To assess the effect of extra-occipital lesions on the local cerebral glucose utilization of the primary and associative visual cortex, 29 patients were studied in the unstimulated state by positron emission tomography and [18F]2-deoxyglucose. Quantitative Goldmann perimetry was done in each patient at the time of the positron emission tomographic study. Nine patients showed homonymous defects, either hemianopsia or quadrantanopsia, whereas nine patients had heteronymous defects. Eleven control subjects, free of any neurological symptoms and with normal visual fields, were also studied with [18F]2-deoxyglucose positron emission tomography. In the normal control subjects and in patients with a heteronymous defect, left-to-right differences in the local cerebral metabolic rate for glucose of the visual cortex varied less than 10%. In patients with hemianopic defects, differences ranged from 8 to 38%, with the hypometabolic cortex always contralateral to the field defect. In patients with quadrantanopic defects, the visual cortex contralateral to the field defect demonstrated differences from 14 to 24% above and below the calcarine fissure, the cortex that received greater input from the affected field being hypometabolic.