Incomplete hippocampal inversion: diagnostic criteria and effect on epilepsy, seizure localization and therapeutic outcome in children.

PURPOSE: Elaborate a simple Magnetic Resonance Imaging (MRI)-based score to define Incomplete Hippocampal Inversion (IHI) in children (Phase 1), and evaluate the relation of IHI with (A) epilepsy, (B) seizure localization and (C) therapeutic response in a paediatric population (Phase 2).

METHODS

In Phase 1, incompletely inverted hippocampi were matched to completely inverted hippocampi. Multiple qualitative and quantitative hippocampal and extra-hippocampal features were evaluated in coronal-oblique T1-weighted (T1W) and coronal T2-weighted (T2W) images. Multivariate analysis was performed to elaborate the MRI-based score to define IHI. In Phase 2, epilepsy patients were matched to controls, and the T1W and T2W scores were applied. Multivariate analysis was performed to assess the relation of IHI and epilepsy, seizure localization and therapeutic response.

RESULTS

The hippocampal diameter ratio and parahippocampal angle in the coronal-oblique T1-weighted images, and the hippocampal diameter ratio and collateral sulcus depth in the coronal T2-weighted images predicted IHI in Phase 1. Simple and practical imaging-based scores were developed and are available on the website: https://ihiscore.netlify.app/. The Area Under the Receiver Operating Characteristic Curve of the T1W and T2W scores were, respectively, 0.965 and 0.983. In Phase 2, IHI independently predicted epilepsy (OR = 3.144, 95% CI = 1.981-4.991, p < 0.001), temporal lobe epilepsy (OR = 4.237, 95% CI = 1.586-11.318, p = 0.004), and drug resistant epilepsy (OR = 7.000, 95% CI = 2.800-17.500, p < 0.001).

CONCLUSION

The association between IHI and temporal lobe epilepsy (and the lack of association with extra-temporal epilepsy) favours the possibility of a relation between IHI and the pathophysiology of seizures in epileptic patients. Furthermore, IHI is a potential prognostic marker for therapeutic response in epilepsy.