Clinical, Radiological, and Demographic Details of Benign External Hydrocephalus: A Population-Based Study

Benign external hydrocephalus has an incidence of about 0.4 per 1000 live births. It affects infants and is characterized by an increasing head circumference and typical neuroimaging findings. Previously published studies on benign external hydrocephalus often contain groups of few and selected patients.

This is a follow-up of a recently published article reporting the incidence of benign external hydrocephalus. This retrospective and population-based study covers two large health regions in Norway, over a 10-year period (1994 to 2003). Infants with increasing head circumference, combined with typical radiological findings of enlarged subarachnoid spaces, were included. Information about head circumference development, neuroimaging findings, and birth delivery methods, as well as demographic details, was retrieved from the hospital medical records.

A total of 176 children with benign external hydrocephalus were included, 86.4% being boys. At birth, the head circumference was close to normal. Mean age for when the head circumference reached abnormal values, i.e., crossing two percentiles or reaching the 97.5 percentile, was 3.4 months; none was older than seven months. Around four of five children had dilated lateral ventricles in addition to enlarged subarachnoid spaces. The neuroimaging findings tended to normalize after age 12 months. About half of the patients ended up with head circumferences at or above the 97.5 percentile.

Most infants with benign external hydrocephalus are born with a normal head circumference that increases too fast and reaches abnormally high values before age six months. This age and gender distribution is very similar to that described for infant subdural hemorrhage.