Microdysgenesis with abnormal cortical myelinated fibres in temporal lobe epilepsy: a histopathological study with calbindin D-28-K immunohistochemistry

Microdysgenesis is a microscopic cortical malformation reported to occur wi th varying incidence in surgical lobectomies from patients with temporal lo be epilepsy (TLE). It may act as a substrate for the seizures. Four patient s are reported with TLE, hippocampal sclerosis and cortical microdysgenesis which was also characterized by the presence of abnormal myelinated fibres running tangentially in the superficial cortical laminae and closely assoc iated with abnormal clusters of neurones. Similar abnormal cortical fibres have been described in other malformations of cortical development includin g polymicrogyria and focal cortical dysplasia and it is therefore likely th at these fibres represent part of the microdysgenetic malformation not hith erto reported. The possibility is discussed that they may also be of functi onal significance in terms of influencing local seizure propagation and the secondary cortical neuronal loss observed, predominantly affecting layer I I. Studies of calbindin interneuronal populations showed preservation of th ese cells in the microdysgenetic cortex, when compared with non-malformed t emporal lobes, despite an overall reduction in cortical neuronal density. I n addition, prominent numbers of neurogliaform calbindin-positive nerve cel ls were observed in the microdysgenesis cases and the nature of these cells is speculated upon.