[Complex visual hallucinations in the hemianopic field following an ischemic lesion of the occipitotemporal base--confirmation of the lesion by MRI and speculations on the pathophysiology].

We report a patient who presented with complex visual hallucinations in the right hemianopic field following an infarction in the left occipitotemporal base. A 73-year-old right-handed woman developed right homonymous hemianopia. A week after its onset, she noticed a strange man with glasses, or a man wearing a gray hat and a black coat standing in the defective visual field. Such visual images later included a nurse, a large hand extending from the right side to the center, and many pieces of cloth descending from the roof. Most of these objects were unfamiliar to her, but may have been related to previous experiences. Her hallucinations were usually black and white singular and motionless, and sometimes consisted of multiple identical replications of objects. All of the hallucinations vanished when the patient tried looking directly at them. An EEG failed to showed any epileptic discharges. T1-weighted MRI with gadolinium-DTPA performed nine days after the onset revealed a localized high-signal-intensity region suggesting an infarction around the left collateral sulcus that included part of the lingual gyrus and the fusiform gyrus. 123I-IMP SPECT showed hypoperfusion of the left occipitotemporal base. The hallucinations gradually resolved a month after the onset, but the right homonymous hemianopia persisted. The enhanced lesion on T1-weighted images was no longer visible on MRI performed a month after the onset but, remained high-intensity on the T2-weighted images. There have been reports of complex visual hallucinations in hemianopic fields, but there have been only a few reports in which the responsible lesion was discussed on the basis of the CT and MRI findings. The findings in our patient suggest that lesions of the occipitotemporal base are one of the possible causes of this symptom. Taken together with earlier reports, not only pure release phenomena but irritative phenomena in the association visual cortex may be involved in the complex visual hallucinations in the hemianopic field, as Lance and Kölmel suspected.