= collection of cortical neurons in an abnormal location ← arrest of migrating neuroblasts from ventricular walls to brain surface between 7–24 weeks of GA

Frequency: 3% of healthy population

May be associated with: agenesis of corpus callosum, aqueductal stenosis, microcephaly, schizencephaly

• seizures

Location:

1. nodular form: usually symmetric bilaterally in subependymal region / periventricular white matter with predilection for posterior + anterior horns
2. laminar form: deep / subcortical regions within white matter (less common)

• single / multiple bilateral subependymal nodules along lateral ventricles
• isointense with gray matter on all sequences, NO surrounding edema, NO contrast enhancement

DDx: subependymal spread of neoplasm, subependymal hemorrhage, vascular malformation, tuberous sclerosis, intraventricular meningioma, neurofibromatosis