Commonest cause of obstructive hydrocephalus in children –
**Core Concept**
Obstructive hydrocephalus in children often results from an interruption in the cerebrospinal fluid (CSF) pathway, leading to accumulation of CSF and increased intracranial pressure. This condition can be caused by various factors, including tumors, cysts, or physical obstructions within the ventricular system.
**Why the Correct Answer is Right**
The most common cause of obstructive hydrocephalus in children is a posterior fossa tumor, particularly a medulloblastoma. These tumors arise from the cerebellum and can block the flow of CSF through the fourth ventricle, leading to hydrocephalus. The tumor's location and growth pattern can compress the aqueduct of Sylvius, preventing CSF from flowing from the third to the fourth ventricle.
**Why Each Wrong Option is Incorrect**
**Option A:** Arachnoid cysts can cause non-obstructive hydrocephalus by allowing CSF to egress from the ventricles, but they are not the most common cause of obstructive hydrocephalus in children.
**Option B:** Meningitis can cause communicating hydrocephalus by impairing CSF reabsorption, but it is not a common cause of obstructive hydrocephalus.
**Option C:** Congenital aqueductal stenosis is a rare cause of obstructive hydrocephalus, often presenting at birth or in early childhood.
**Clinical Pearl / High-Yield Fact**
The presentation of obstructive hydrocephalus in children can include symptoms such as irritability, vomiting, and macrocephaly (enlarged head circumference). A high index of suspicion is essential for early diagnosis and treatment.
**Correct Answer:** D.