Other Disorders Of Neuronal Migration And Cortical Formation

Ulegyria is another distinct cortical anomaly. Ulegyria is best characterized as a fusion of layer 1 at the depths of sulci with relative sparing of the crests of the gyri. The fusion is frequently associated with gliosis in the cortex, neuronal loss, and obliteration of the cortical lamination. The scarring at the depth of a sulcus and sparing at the surface of the brain results in a mushroom appearance when the gyrus is viewed on cross section. These lesions have very well-defined borders and discrete islands of preserved neurons within the lesion. The histology and location, frequently in an arterial zone, have led to the contention that ulegyria arises late in gestation or in early neonatal life as a vascular injury to the immature cortex, possibly related to hypoperfusion. Ulegyria may be clinically silent or manifest as seizures, similar to those of polymicrogyria discussed earlier.

An enlarged brain volume, or megalencephaly, can be sporadic, autosomal dominant, autosomal recessive, or part of a recognized syndrome or disease (...Ta.ble 2.8.-3. ).'7i Generalized megalencephaly shows a diffuse broadening of the cerebral gyri with an increased white matter and gray matter volume and frequently normal-sized ventricles. The brain is usually microscopically normal, although several reports have suggested an increased cell volume. In the familial form of megalencephaly with autosomal dominant inheritance, the majority of cases are neurologically normal. Hydrocephalus and extracerebral fluid collections have to be ruled out by imaging in all cases.

Hemimegalencephaly ( Fig 2.8-9 ) may occur in isolation or may be associated with a specific syndrome, the most

_TABLE 28-3 -- SELECTED CONDITIONS PRESENTING WITH MEGALENCEPHALY AND HEMIMEGALENCEPHALY

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