Benign enlargement of sub-arachnoid spaces in infancy

Benign enlargement of sub-arachnoid spaces (BESS) is one of the causes of macrocephaly in infants. It is a self-limiting condition and does not require any active medical or surgical treatment. We report a case of an infant aged 4 months who was referred for magnetic resonance imaging (MRI) of the brain as the head circumference of the infant had increased rapidly from the 50(th) percentile in the 3(rd) month to more than the 95(th) percentile in the 4(th) month of age. MRI revealed enlarged anterior sub-arachnoid spaces and mild prominence of all the ventricles. A possibility of BESS was suspected since the child was neurodevelopmentally normal. A follow-up MRI done at the age of 18 months showed a reduction in the size of the sub-arachnoid spaces with normal sized ventricles.