Which of the following is an early sign of hydrocephalus in newborns?

Bulging fontanel is an early sign of hydrocephalus in newborns because it indicates increased intracranial pressure, which can occur when there is an accumulation of cerebrospinal fluid (CSF) within the ventricles of the brain. The fontanels, or soft spots on a baby's skull, are areas where the bones have not yet fused. This flexibility allows for the rapid growth of the infant's brain during the early months of life, and when there is excess fluid, the pressure can cause the fontanel to bulge outward.

In contrast, normal head circumference would not indicate hydrocephalus, as this condition typically presents with a larger than average head size due to the increased fluid. Lazy eye, while a potential sign of various neurological issues, is not specifically indicative of hydrocephalus in newborns. Excessive weight gain is unrelated to hydrocephalus and more indicative of nutritional issues or metabolic conditions. Therefore, the presence of a bulging fontanel serves as a critical warning sign for potential hydrocephalus and should prompt further evaluation and monitoring.