Abstracts

Malformations of cortical development (MCD) are divided into those resulting from abnormal cell proliferation, neuronal migration, and cortical organization. Abnormalities of hippocampal shape and positioning in MCD have been reported in few reports which included mostly patients with heterotopia. The occurrence of such changes in the different MCD groups and in healthy subjects has not been systematically studied.
Our purpose was to investigate shape and positioning characteristics of the hippocampal formation in healthy subjects and patients with MCD using high-resolution MRI.
We studied 76 patients with MCD, including focal cortical dysplasia (n=29), heterotopia (n= 30) and polymicrogyria (n=17). Patients were compared to 50 age- and sex-matched healthy control subjects. T1-weighted three-dimensional MR images were presented in random order to two trained observers who were unaware of the final diagnosis and a consensus report was obtained. Abnormalities of shape and positioning of the hippocampal formation were evaluated at the level of the hippocampal head, body and tail, and were diagnosed on the presence of 12 recognized criteria. These criteria were based on the evaluation of the hippocampus, the parahippocampal gyrus, the collateral sulcus and the subiculum. A subject was considered abnormal if at least two of the criteria were found. Group differences between patients and controls were assessed using Chi-square.
7/50 (14%) healthy control subjects and 42/76 (55%) of MCD patients (p[lt] 0.01) were found to have abnormal findings. This was true for patients with heterotopia (20/30=67%; p[lt]0.0001), polymicrogyria (9/17=53%; p=0.001) and focal cortical dysplasia (13/29=45%; p=0.006). We found a significant association between 11 criteria and MCD (p[lt]0.05). No association was found between any criteria and healthy control subjects. Abnormalities were observed in all segments of the hippocampal formation.
There was a weak association between the side of MCD and EEG focus (p=0.04). No association was found between side of hippocampal abnormalities and side of MCD lesion or EEG focus.
Abnormalities of hippocampal shape and positioning occur in more than half of patients with MCD, but can also be found in a small proportion of healthy subjects.
The fact that hippocampal abnormalities are present in equal proportion among different MCD groups suggests an underlying diffuse altered brain developmental process common to all MCD. Yet, abnormalities of hippocampal shape and positionning seem unrelated to the epileptogenic area.