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. 

Differential diagnosis

• Taylor dysplasia