Magnetic resonance fast spin-echo imaging (MRI) was performed after complex febrile convulsions (CFCs) in 27 infants treated at Duke University Medical Center, Durham, NC. Of 15 with focal CFCs 6 had abnormal MRIs, and of 12 infants with generalized CFCs all had normal MRIs. Of the 6 infants with focal CFCs and abnormal MRIs, 2 showed perinatal preexisting bilateral hippocampal atrophy, and 4 had acute edema and T2-weighted increased hippocampal signal intensity in the focus of seizure origin. The 4 with acute edema had suffered longer duration seizures than the other infants, and their follow-up MRIs showed hippocampal atrophy. [1]

COMMENT. The findings confirm previous reports that complex febrile convulsions may sometimes be related to preexisting perinatal brain lesions, and in some cases the prolonged focal seizure can result in acute injury followed by atrophy or sclerosis of the hippocampus. The acute hippocampal changes on MRI followed by evidence of chronic mesial temporal sclerosis suggest a causal connection in a minority of cases of focal prolonged complex febrile seizures. Shinnar S, in his editorial, stresses the unusually long duration of the seizure in these patients (100 minutes) [2]. Only long-term follow-up will determine whether or not these patients will develop temporal lobe, complex partial epilepsy.

Temporal lobe lesions missed by MRIs. The failure of conventional MRI in diagnosing hippocampal sclerosis in adults with refractory temporal lobe seizures is reported from the University of Rochester School of Medicine and Strong Memorial Hospital [3]. Of 34 patients with normal reports on MRIs performed outside an epilepsy center, 32 were abnormal when repeated by special protocol (no gaps) imaging. This report points to probable MRI misdiagnosis and a further potential error in research concerning hippocampal injury with febrile seizures.

Interictal EEG spikes for seizure lateralization in mesial temporal lobe epilepsy. In a study of 21 patients at the Universitatsklinik fur Neurologie, Vienna, Austria, lateralization of clinical seizures was correct (ipsilateral to side of hippocampal sclerosis) in almost 100% of cases with unitemporal spikes and in only 50% of those showing bitemporal spikes. [4]