[An unusual case of epilepsy exhibiting gelastic seizure, simple visual hallucination, and transient swelling of the left parieto-occipital region].

We report a 74-year-old man with gelastic seizure, simple visual hallucination, and adversive seizure. The patient described his visual hallucinations as "rotating light like a firefly" and "mimicking a stream". Brain CT scan showed a transient swelling as well as low density of a left parieto-occipital region. Electroencephalographic study revealed spikes and fast waves beginning at left occipital region. Although temporal lobe and hypothalamic lesions (especially hypothalamic hamartomas) are well known as origins of gelastic seizures, we could not find any report that described a series of occurrence of gelastic seizure and simple visual hallucination. Usually, simple visual hallucination is thought to occur in occipital lesion. In our case, it is possible that gelastic seizure and simple visual hallucination are related to the epileptic discharge from occipital lesion directly or indirectly. The reversible brain swelling with low density seen in the present case might be caused by cytotoxic edema due to status epilepticus.