Sisodiya, Sanjay Mull; (1996) Qualitative and quantitative analysis of MRI data from patients with epilepsy. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

Cerebral dysgenesis is the second commonest cause of refractory epilepsy, but its identification and the definition of its anatomical boundaries, though clinically important, remain problematical. This thesis investigates new methodologies for analysis of structural MRI data in normal subjects and patients with partial epilepsy due to known or suspected focal abnormalities and examines the following hypotheses: informative structural patterns and proportionalities in the normal brain should be quantitatively demonstrable. structural abnormalities in the brain affected by cerebral dysgenesis may extend beyond visualised boundaries of the apparently focal lesion itself. postprocessing of MRI data should reveal more abnormalities, qualitative and quantitative, than are found by visual inspection alone, including abnormalities in apparently normal scans of some patients with focal epilepsy. Subjects studied were: healthy controls (33); patients with: dysgenesis (35); focal epilepsy and apparently normal scans (45); patients with a different cause for epilepsy, without obvious dysgenesis (hippocampal sclerosis; 16). Qualitative analysis was performed by reconstruction of data into three-dimensional surface renderings and inspection for surface gyral pattern abnormalities. Novel methodologies (grey, white matter volume distributions; surface areas; callosal areas; surface-volume relationships) were devised for the quantitative analysis of cerebral anatomy. Methodological problems and biases are considered. Extensive quantitative structural order was found in brains from normal subjects; using the chief methodology devised, evidence supporting the hypothesis of widespread structural abnormality was found in 70% of patients with dysgenesis, no controls and no patients with isolated hippocampal sclerosis. More subtle abnormalities were also revealed in all patient groups using measures of surface-volume proportionalities. Using all methods some abnormality of structure was revealed in 56% of patients with apparently completely normal scans. The biological basis and clinical relevance of these findings is discussed. Extensive abnormalities in dysgenesis may be due to widespread alteration in the normal pattern of connections in the brain.

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