Mystery case: Bilateral posterior periventricular heterotopias.

A 33-year-old man presented with a 2-year history of focal seizures. A previous brain MRI scan was reported to show dilatation of 3rd and 4th ventricles with possible aqueduct stenosis and tonsilar ectopia. Repeated brain MRI revealed bilateral posterior periventricular nodular heterotopias (pPNH), a malformation of cortical development, lining the occipital and temporal horns of both ventricles (figure, A–F), which was retrospectively visible in the first MRI scan. pPNH may present with epilepsy but can easily be missed. White matter volume decreases and other associated brain abnormalities are often seen in pPNH and should prompt careful review of the periventricular region.1 Epilepsy surgery in bilateral pPNH has a less favorable outcome.2