Periventricular nodular heterotopia (PNH) is the most common clinically encountered heterotopia and makes up 15-20% of all cortical dysgenesis series. The majority of patients with PNH have seizures or epilepsy. Abnormal cellular representation and connectivity of interneurons in heterotopia may explain or contribute to epileptogenicity of PNH. Several groups have advocated a subclassification of PNH using radiological grounds, based on contiguity and symmetry of nodules, or the clinical and genetic associations. Brain computerized tomography (CT) would usually demonstrate the malformation in cases of diffuse and contiguous PNH but can miss more subtle and focal types. Neuropsychological testing is useful to identify specific domains of deficiency in patients who display signs of neurological developmental delay. Fluoro-deoxy-glucose positron emission tomography (FDGPET) and single positron emission computerized tomography (SPECT) have shown that the metabolic activity and perfusion to the nodules are identical to that of the overlying cortex.