Neuroanatomic correlates of visual hallucinations in poststroke hemianopic patients

Homonymous hemianopia (HH) is the most frequent visual-field defect after a stroke. Some of these patients also have visual hallucinations, the origin and frequency of which remain largely unknown. The aims of this work were to determine the occurrence of visual hallucinations among poststroke hemianopic patients in function of the location (Brodmann areas) of the brain lesion, as determined by MRI, and to study the neuroanatomic correlates of these hallucinations by nature, frequency, and type.

One hundred sixteen patients with HH who had had a stroke in the posterior region, including the occipital lobe, participated in the study. We evaluated the frequency and nature of visual hallucinations with the Questionnaire for Hallucinations in Homonymous Hemianopia. The volume of each patient's brain lesion was modeled in 3 dimensions.

Of 116 patients with an HH from a cortical infarction, 85 were excluded due to confounding factors associated with hallucinations. In the final cohort of 31 patients matched for lesion location and etiology, 58% had experienced hallucinations. A significant inverse correlation between lesion size and the frequency of visual hallucinations emerged. The presence of visual hallucinations in poststroke hemianopic patients requires a relatively small lesion that includes, at the very least, loss of the striate cortex but that spares Brodmann area 19, 20, and 37.

Our results suggest that visual hallucinations might be due to complex interactions between damaged areas and intact areas of the visual cortex. We discuss these findings regarding models of perception and of visual recognition. Our results also have implications for the clinical care of patients with HH who have had a stroke.