Hippocampal malrotation with normal corpus callosum: a new entity?

Abstract

Among 527 MRI examinations of patients with a suspicion of epilepsy in 5 years, we found 32 cases of hippocampal malrotation (HIMAL). The characteristic features are: incomplete inversion of the hippocampus with and abnormally round shape; unilateral involvement of the whole hippocampus; normal signal intensity and size; blurred internal structure; an abnormal angle of collateral sulcus; abnormal position and size of the fornix; normal size of the temporal lobe; enlargement and particular configuration of the temporal horn, typical of corpus callosum agenesis; and a normal corpus callosum. In 7 cases (22%) HIMAL occurred together with developmental disorders. It was predominantly seen in men. The clinical features were varied. Based on some MRI features, the presence of developmental disorders, the male predominance, the frequently positive family history, and a review of the literature, we think HIMAL may be the consequence of a mild hemisphere developmental disorder. It is probably not the basic cause of epilepsy in such varied clinical setting, but may be a sign of a developmental disorder and can help in selecting patients for more meticulous investigation. It also may give some new understanding of brain development.

Evaluation of hippocampal infolding angle and incomplete hippocampal inversion in pediatric patients with epilepsy and febrile seizures

“…This morphologic evaluation for IHI included a hippocampus with an abnormally rounded shape but a normal size and signal intensity. Also, other features of IHI, including enlargement of the temporal horn tip, collateral sulcus orientation, collateral white matter position, and ipsilateral fornix position were analyzed according to relevant literature (2,5,6). Collateral white matter has a lateral position to the hippocampus and the ipsilateral fornix has a lower position in patients with IHI.…”

Mesial temporal lobe morphology in intractable pediatric epilepsy: so-called hippocampal malrotation, associated findings, and relevance to presurgical assessment

“…9 This morphology has been variously described depending on the defining criteria chosen in each study (e.g., "hippocampal malrotation," or HIMAL, "incomplete hippocampal inversion," or "hippocampal morphologic modification"). 1,2,4,5,12,20 Imaging criteria for HIMAL have varied but have typically included asymmetrical medialized rounded hippocampal shape, vertical collateral sulcus, internal architecture blurring, and ipsilateral low fornix position. 1,2,12 Prior studies have reported a wide variation in HIMAL prevalence, from 1%-19% in healthy controls to 6%-30% in patients with epilepsy (mostly adult studies), 1,2,5,31 with the highest prevalence in significant anomalies of brain development (64%-85%).…”

Presurgical Assessment of Patients with Refractory Temporal Lobe Epilepsy

“…Defined in 2000 by Barsi et al as a group of ten characteristics: incomplete hippocampal investment with rounded shape, unilateral commitment, signal intensity and normal size, internal structure blurred, abnormal angle collateral sulcus, anomalous fornix size and position, temporal lobe size preserved, temporal horn enlargement and normal corpus callosum (Barsi, 2000) [ Fig. 6].…”