**Core Concept**
Delayed expansion in the context of cranioplasty or cranial vault reconstruction refers to the gradual increase in intracranial volume following the closure of cranial sutures. This process typically occurs in infants and young children, leading to an increase in intracranial pressure.

**Why the Correct Answer is Right**
Delayed expansion is a normal physiological process in early childhood, allowing for brain growth and development. As the cranial sutures close, the intracranial volume increases, which can lead to an increase in intracranial pressure. However, this process is self-limiting and resolves once the cranial sutures fuse. The exact mechanisms behind delayed expansion involve changes in cerebrospinal fluid dynamics, brain elasticity, and the closure of cranial sutures.

**Why Each Wrong Option is Incorrect**
**Option A:** Delayed expansion is not typically associated with increased risk of hydrocephalus, as it is a normal part of cranial growth and development.
**Option B:** Delayed expansion does not require surgical intervention, as it is a self-limiting process that resolves once the cranial sutures fuse.
**Option C:** Delayed expansion is not a sign of increased intracranial pressure due to a space-occupying lesion, as it is a normal physiological process.

**Clinical Pearl / High-Yield Fact**
Delayed expansion in infants and young children is a normal part of cranial growth and development, and it does not require surgical intervention. Clinicians should be aware of this process to avoid unnecessary diagnostic testing and treatment.

**Correct Answer: D.**