Subcortical heterotopia

Subcortical heterotopia is a form of nodular grey matter heterotopia. They can be divided into:

• nodular form: extend from the ventricle into the white matter
• curvilinear form: extend from the cortex into the underlying white matter
• mixed form

Terminology

The term laminar heterotopia is sometimes used ambiguously to refer to some of these patients ⁴. It is important to note that these patients should not be confused with lissencephaly type I-subcortical band heterotopia spectrum which is distinct on both imaging and at an underlying genetic level. 

Clinical presentation

Epilepsy is very common and typically presents in childhood ³. It is usually associated with variable developmental delay ³. 

Radiographic features

Subcortical heterotopias are continuous with the overlying cortex or underlying ventricle ² and are associated with severe abnormalities of the involved hemisphere, characterized by ¹:

• diffuse reduction in size of the hemisphere
• distorted ventricles
• diminished and abnormal white matter
• thinned overlying cortex with shallow sulci
• distorted basal ganglia

These features are helpful in distinguishing this entity from subependymal grey matter heterotopia and lissencephaly type I-subcortical band heterotopia spectrum.