Infantile Macrocephaly: Complicated Familial Benign Enlargement of Subarachnoid Space in Twins of Suspected Nonaccidental Injury.

A 3-month-old first of dizygotic male twins, born at 34 + 5 weeks gestational age, presented with a 4-week history of increasing head circumference and vomiting. He had a tense anterior fontanelle and a head circumference above the 97th percentile. Magnetic resonance imaging showed large bilateral subdural collection with hemosiderin deposits suggestive of hemorrhage. Nine days of bilateral subdural drainage reduced the collection size and blood load. On postoperative day 16, magnetic resonance imaging confirmed persistent but smaller subdural collections, unmasking the underlying subarachnoid space enlargement. On day 18, a right subdural-peritoneal valveless shunt was inserted as definitive treatment. As part of a nonaccidental injury investigation, Twin 2 was also found to have macrocephaly secondary to benign enlargement of subarachnoid space, which was managed conservatively. Benign enlargement of subarachnoid space has an assumed autosomal/multifactorial inheritance and predisposes to subdural hemorrhage. Ultimately, no safeguarding issues were raised. Both twins continued to be neurologically stable at 2-year follow-up with head circumferences between the 98th and 99th percentiles.