Microdysgenesis--relevant finding in refractory epilepsy? A response to S. H. Eriksson et al., Acta Neuropathologica (2002) 103:74-77

Preferential susceptibility of limbic cortices to microstructural damage in temporal lobe epilepsy: A quantitative T1 mapping study

The majority of MRI studies in temporal lobe epilepsy (TLE) have utilized morphometry to map widespread cortical alterations. Morphological markers, such as cortical thickness or grey matter density, reflect combinations of biological events largely driven by overall cortical geometry rather than intracortical tissue properties. Because of its sensitivity to intracortical myelin, quantitative measurement of longitudinal relaxation time (qT₁) provides and an in vivo proxy for cortical microstructure. Here, we mapped the regional distribution of qT₁ in a consecutive cohort of 24 TLE patients and 20 healthy controls. Compared to controls, patients presented with a strictly ipsilateral distribution of qT₁ increases in temporopolar, parahippocampal and orbitofrontal cortices. Supervised statistical learning applied to qT₁ maps could lateralize the seizure focus in 92% of patients. Intracortical profiling of qT₁ along streamlines perpendicular to the cortical mantle revealed marked effects in upper levels that tapered off at the white matter interface. Findings remained robust after correction for cortical thickness and interface blurring, suggesting independence from previously reported morphological anomalies in this disorder. Mapping of qT₁ along hippocampal subfield surfaces revealed marked increases in anterior portions of the ipsilateral CA1-3 and DG that were also robust against correction for atrophy. Notably, in operated patients, qualitative histopathological analysis of myelin stains in resected hippocampal specimens confirmed disrupted internal architecture and fiber organization. Both hippocampal and neocortical qT₁ anomalies were more severe in patients with early disease onset. Finally, analysis of resting-state connectivity from regions of qT₁ increases revealed altered intrinsic functional network embedding in patients, particularly to prefrontal networks. Analysis of qT₁ suggests a preferential susceptibility of ipsilateral limbic cortices to microstructural damage, possibly related to disrupted myeloarchitecture. These alterations may reflect atypical neurodevelopment and affect the integrity of fronto-limbic functional networks.

Parenchymal lesions in pharmacoresistant temporal lobe epilepsy: dual and multiple pathology

OBJECTIVES

Dual pathology is reported in 5-30% of temporal lobe resections performed in pharmacoresistant epilepsy. Dual pathology may be of importance for surgical planning and also for the understanding of the pathogenesis of epilepsy. We describe the frequency of dual or multiple pathology, i.e. more than one histopathological diagnosis, in adults with temporal lobe resections.

MATERIAL AND METHODS

Surgical specimens from 33 consecutive patients with resections including mesial as well as neocortical temporal structures were reviewed. All histopathological findings were recorded. Post-mortem specimens from 11 control subjects were also reviewed.

RESULTS

Dual or multiple pathology was found in almost half of the epilepsy patients (48%). Hippocampal sclerosis was found in 25 patients (76%), malformations of cortical development in 15 (46%), of which 12 (36%) were microdysgenesis, and low-grade tumours in seven (21%). Apart from mild gliosis, there were no histopathological changes in the control specimens.

CONCLUSION

Dual or multiple pathology was a common finding in this group of adults with temporal lobe resections. In order to increase our understanding of how aetiological factors may combine in the development of seizures, we consider it relevant and important to report all histopathological findings in epilepsy surgery series.