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Paracentral homonymous hemianopic scotoma caused by anterior choroidal artery infarction.

A 71-year-old man experienced an acute onset of difficulty in reading letters in the right visual field. His past medical history included hypertension and diabetes mellitus. The general examination was unremarkable. On neurological examination, paralysis, sensory disturbance and ataxia were not present. History of present illness inspired us right homonymous hemianopsia, and subsequent Humphrey visual field test indeed revealed right paracentral homonymous hemianopic scotoma (Figure 1A), which is typically caused by a lesion in the occipital pole. Brain MRI, however, showed acute infarction in the origin of the optic radiation, consistent with left anterior choroidal artery (AChA) territory (Figure 1B). Laboratory data revealed a normal lipid profile and prothrombin time. HbA1c was 7.4%. The etiology of AChA territory infarction is usually small vessel disease. Hemiparesis, hemisensory impairment and hemianopsia are the triad of AChA territory infarction. One or more of the three symptoms can be absent, but visual field defects are less common than the other cardinal symptoms and cases presenting solely with visual field defects are quite rare. Visual field defects related to AChA territory infarction are variable and include upper quadrantanopia, sectoranopia and homonymous hemianopia with or without macular sparing. Brain MRI of our case revealed a lesion in the origin of the optic radiation supplied by the superior branches of the cisternal segment of AChA. In the optic radiation, the anterior bundle (temporal fascicle) conveys contralateral superior quadrant visual information. A small lesion confined in the anterior bundle of the optic radiation, probably caused by arteriosclerosis of a small branch of AChA, may plausibly explain the pure presentation of paracentral homonymous hemianopic scotoma.