Specific Imaging Findings

Nodular heterotopia (NH) may be located in subependymal or subcortical locations. The subependymal type (periventricular nodular heterotopia, PNH) is the more common one. The lesions show signal intensity that follows the gray matter on all MRI sequences, best seen on T1-weighted inversion recovery and FLAIR images. The nodules do not calcify or enhance with contrast and there is no associated edema. PNH lesions are typically located along the walls of the lateral ventricles causing indentation of the lateral ventricular contours. PNH is most commonly found in the peritrigonal region, it may be unilateral or bilateral, and the number and distribution of lesions varies, from a single one to a few scattered heterotopias to almost continuous nodules. The surrounding white matter and the overall appearance of the cerebral hemisphere is otherwise normal. Subcortical NH (SNH), on the other hand, shows irregular lobulated masses in the subcortical white matter, usually continuous with the overlying cortex and underlying ventricular surface without intervening normal white matter. The overlying cortex is usually thin with shallow sulci. The size of SNH heterotopias varies from a focal small lesion to a conglomerate of abnormal gray matter that involves a large part of the hemisphere. The ipsilateral hemisphere and basal ganglia may be of decreased volume.

Pertinent Clinical Information

BilateralNHis an X-linked dominant disorder with predominance in females due to a near total male mortality during embryogenesis. Clinical related symptoms are epilepsy, intelligence ranging from normal to borderline mental retardation, and coagulopathy. Sporadic heterotopias are associated with seizures and developmental delay, which varies with the severity of brain involvement. Heterotopias may be seen in conjunction with other brain malformations and syndromes, especially the subcortical type.