Incomplete hippocampal inversion—is there a relation to epilepsy?

Abstract

Incomplete hippocampal inversion (IHI) has been described in patients with epilepsy or severe midline malformations but also in nonepileptic subjects without obvious developmental anomalies. We studied the frequency of IHI in different epilepsy syndromes to evaluate their relationship. Three hundred patients were drawn from the regional epilepsy register. Of these, 99 were excluded because of a disease or condition affecting the temporal lobes or incomplete data. Controls were 150 subjects without epilepsy or obvious intracranial developmental anomalies. The coronal MR images were analysed without knowledge of the clinical data. Among epilepsy patients, 30% had IHI (40 left-sided, 4 right-sided, 16 bilateral). Of controls, 18% had IHI (20 left-sided, 8 bilateral). The difference was statistically significant (P < 0.05). Of temporal lobe epilepsy (TLE) patients, 25% had IHI, which was not a significantly higher frequency than in controls (P = 0.34). There was no correlation between EEG and IHI laterality. A total of 44% of Rolandic epilepsy patients and 57% of cryptogenic generalised epilepsy patients had IHI. The IHI frequency was very high in some epileptic syndromes, but not significantly higher in TLE compared to controls. No causality between TLE and IHI could be found. IHI can be a sign of disturbed cerebral development affecting other parts of the brain, maybe leading to epilepsy.

Asymmetric Development of the Hippocampal Region Is Common: A Fetal MR Imaging Study

“…A vertical orientation was seen unior bilaterally in 58% of the fetuses in our cohort that presented a well-defined sulcus, a slightly larger number (P ϭ .045) than the 36% described for children or adult populations. 13 Also, this vertical orientation occurred more commonly on the left side, thus suggesting the possibility of a transitional phase toward a more mature horizontally oriented axis. However, this proposed hypothesis could not be confirmed within our own cohort because we failed to find any significant association between the GA and the percentage of vertical collateral sulci.…”

“…7,12,13 Most of the population has an oval hippocampus with a horizontal long axis, a shape we classified as "oval." All other shapes were classified as "nonoval.…”

“…We believe that hippocampi with nonoval shapes most likely represent IHI; indeed, some hippocampi never reach the complete inverted shape even in adulthood. 12,13 The frequency of IHI has been shown to be as high as 14%-20% in preterm neonates at GWs 25-36 in the sonographic study 7 and 19% in MR imaging series of children and adults. 12,13 These frequencies are best comparable with the frequency of the uni-or bilateral nonoval hippocampi in the fetuses in which both hippocampal sulci were closed (from GW 33 onward).…”

“…7 However, the nonoval shape can be seen throughout life in 19% of the general population, most often on the left side. 12,13 The aim of this study was to evaluate the development of the hippocampal region in fetuses by using MR imaging.…”

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.…”