Intracranial extracerebral glioneuronal heterotopia with heterotopic cerebellum, glioependymal cyst, and DNA methylation profiling

To the Editor: Intracranial extracerebral glioneuronal heterotopia (IEGH) is a rare developmental lesion with mature or maturing central nervous system tissue outside the brain parenchyma, usually near the leptomeninges and skull base. Other terms include neuroglial heterotopia, glioneuronal choristoma, and ectopic brain tissue. IEGH may mimic congenital brain tumors, teratomas, or encephaloceles but is regarded as a benign malformation. Fewer than 20 cases were identified in a 2014 review, mainly in the anterior or middle cranial fossa, sometimes with associated craniofacial abnormalities, skull-base defects, extracranial extension, cysts, or ectopic tissue.1 Recent reports include a prenatally detected lesion and a middle cranial fossa lesion with infratemporal and oropharyngeal extension.2,3 Molecular data on IEGH remain scarce. We report an IEGH with a glioependymal cyst, highly differentiated heterotopic cerebellum, and DNA methylation profiling. Prenatal ultrasonography at 23 + 2 weeks detected right frontal solid-cystic and nasal cutaneous lesions. Genetic testing following amniocentesis identified no pathogenic abnormality. Fetal MRI showed an 18 × 13 × 13 mm frontal mass and a 5 × 5 × 5 mm nasal soft-tissue lesion. Serial prenatal examinations showed no growth. Delivery was by cesarean section at 38 + 5 weeks; the neurologically intact infant was followed by ultrasonography.