Mild malformations of cortical development (mMCD), previously known as microdysgenesis 4, correspond to microscopic malformations of cortical development with heterotopic neurones and an abnormal cortical architecture 1.
For a broader view on malformations of cortical development refer on classification system for malformations of cortical development and more specifically focal cortical dysplasia.
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Epidemiology
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Clinical features
It is related as one cause of drug-resistant partial epilepsy 1,3, however mMCD were also described in autopsy studies of asymptomatic patients.
Pathology
mMCD correspond to microscopic changes that constitute cortical laminar disorganisation, abnormal cortical myelinated fibres, neuronal clustering, and heterotypic or excessively numerous neurones in white matter, subcortical areas, or cortical layer I 3.
It is important to emphasises that isolated single neurones are usually present in the white matter of normal brains. On the other hand, a large groups of mispositioned cortical neurones in the white matter are found in types malformations of cortical development associated with epilepsy. mMCD may lie between these extremities, but the point at which white matter neuronal numbers become abnormal and represent a significant malformation is controversial and not well defined 2.
The fact that several types of cortical dysplasia may be observed in the same patient illustrates the complexity of this broad spectrum of pathological processes that affect cortical mantle formation 3.
mMCD is recognised in the Palmini classification of focal cortical dysplasia.
Radiographic features
These features correspond to microscopic abnormalities in which MRI scans usually are normal.
Treatment and prognosis
The literature describes both favourable and worse outcomes after epilepsy surgery in patients with increased numbers of white matter neurones and mMCD 1.
History and etymology
In 1984, Meencke and Janz described microdysgenesis in post-mortem tissue from patients with generalised epilepsy 2,5.
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