A large anterior fontanelle in an infant may indicate what condition?

A large anterior fontanelle in an infant is often associated with certain medical conditions, and among the options provided, hydrocephalus is the most relevant condition. In this context, hydrocephalus refers to an accumulation of cerebrospinal fluid (CSF) in the ventricles of the brain, leading to increased intracranial pressure. The anterior fontanelle, which is the soft spot on the top of the skull, can become enlarged as the pressure rises, causing the skull to expand. This phenomenon occurs because the sutures in an infant's skull are not yet fused, allowing for some flexibility and expansion of the cranial bones.

Conditions like spina bifida may also present with other neurological signs, but they are not directly linked to an enlarged anterior fontanelle in the way that hydrocephalus is. Similarly, hypothyroidism and Down syndrome have different presentations and do not typically result in a prominent increase in the size of the fontanelle. Understanding that the anterior fontanelle serves as an important clinical indicator in assessing neurodevelopmental conditions highlights why hydrocephalus is the correct answer in this scenario.