Benign extra-axial fluid of infancy

Axial T1-weighted image of a term infant who presented with increasing head circumference >97^th percentile for age. The infant was otherwise well-appearing, had no concerning symptoms, and was developing normally. The family history was positive for macrocephaly. Brain MRI demonstrates enlargement of the anterior subarachnoid space with mild ventriculomegaly consistent with benign extra-axial fluid of infancy (also called "benign external hydrocephalus").