Abstract
ObjectivesDebates over the relationship between hippocampal malrotation (HIMAL) and epilepsy continue without consensus. This study explores the role of HIMAL in a cohort of epilepsy caused by focal cortical dysplasia (FCD).MethodsIn this study, 90 patients with epilepsy caused by FCD type I and type II and 48 healthy adults underwent a 3 Tesla MRI following a dedicated epilepsy protocol for the analysis of the prevalence and morphologic features of HIMAL. In addition, numerous clinical characteristics and hippocampal volumes were evaluated.ResultsThe cohort included a total of 90 patients (32 were HIMAL, 58 were non-HIMAL). Among these patients, 32 (35.6%) had HIMAL (22 left, four right, and six bilateral), which did not differ from the 48 controls, where 16 (33.3%) had HIMAL (12 left, two right, and two bilateral). Neither the quantitative features of HIMAL (diameter ratio, dominant inferior temporal sulcus height ratio, medial distance ratio, dominant inferior temporal sulcus angle, and parahippocampal angle), nor the accompanying characteristics of HIMAL (vertical dominant inferior temporal sulcus, enlarged temporal horn, and a low position of ipsilateral fornix) showed differences between patients with FCD and controls. No statistical difference in the clinical characteristics between FCD patients with HIMAL and those without was found. Neither the side nor the existence of HIMAL was correlated with the lateralization and location of FCD. As to the hippocampal volume, there was no difference between FCD patients with HIMAL and those without.ConclusionHippocampal malrotation is a common morphologic variant in healthy controls as well as in patients with epilepsy caused by FCD type I and type II. Hippocampal malrotation could be less significant in epilepsy caused by FCD type I and type II.
Highlights
Hippocampal malrotation (HIMAL), described as incomplete hippocampal inversion, often presents with a round or pyramidal shape, medial position close to the midline, vertical collateral sulcus, and a low position of ipsilateral fornix [1ā3]
HIMAL has not been directly considered as an epileptogenic lesion, it may be a factor of susceptibility to neuropathological processes which lead to the hippocampal neuronal loss and hippocampal sclerosis [12ā14]
We retrospectively reviewed the records of consecutive epileptic patients with Focal cortical dysplasia (FCD) who were admitted to the Epilepsy Center of our hospital between 2013 and 2020
Summary
Hippocampal malrotation (HIMAL), described as incomplete hippocampal inversion, often presents with a round or pyramidal shape, medial position close to the midline, vertical collateral sulcus, and a low position of ipsilateral fornix [1ā3]. It has been reported that patients with periventricular nodular heterotopia, lissencephaly, polymicrogyria, holoprosencephaly, and hemimegalencephaly often have HIMAL [4, 7ā11], and eventually present epilepsy. In patients with FCD type II or type I, it is unclear whether HIMAL provides localization value or has any relationship with the epileptogenic zone. Most research on HIMAL have involved patients with malformation of cortical development [4, 7, 8], and little is known about the involvement of HIMAL in patients with FCD. Under this scenario, addressing the relationship between HIMAL and FCD can contribute to clinical work and fill in knowledge gaps
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