Which of the following signs is most indicative of hydrocephalus in an infant?

Choice A rationale The setting-sun sign is a clinical finding where the infant's eyes appear to be driven downward, with the sclera visible above the iris, resembling the sun setting below the horizon. This is highly indicative of hydrocephalus as the increased intracranial pressure (ICP) presses on the midbrain tectum, causing paralysis of upward gaze. Choice B rationale A high-pitched, shrill cry is a non-specific sign of neurological distress and is often associated with increased intracranial pressure (ICP). While it can occur with hydrocephalus, it is a less specific and less consistent finding than the setting-sun sign, which directly reflects the mechanical pressure effects on the oculomotor and associated midbrain structures. Choice C rationale A sunken or depressed fontanel is a classic sign of dehydration or hypovolemia due to decreased intracranial volume. Conversely, an infant with hydrocephalus, characterized by excessive cerebrospinal fluid accumulation, will typically present with a bulging, tense, and non-pulsatile anterior fontanel due to the severely elevated intracranial pressure. Choice D rationale Normal head circumference would be an unexpected finding in an infant with significant, uncompensated hydrocephalus. The defining clinical feature in infants is the rapid and often exaggerated increase in head circumference (macrocephaly), as the cranial sutures are not yet fused, allowing the head to expand markedly to accommodate the accumulating cerebrospinal fluid and rising pressure.