**Question:** Commonest cause of obstructive hydrocephalus in children -

A. Fetal ventriculomegaly
B. Post-haemorrhagic hydrocephalus
C. Post-meningitic hydrocephalus
D. Post-neuroblastoma hydrocephalus

**Core Concept:** Obstructive hydrocephalus is a condition where the accumulation of cerebrospinal fluid (CSF) leads to increased intracranial pressure, causing brain enlargement and potential neurological impairment. It can be classified into three types: obstructive, communicating, and non-communicating hydrocephalus. Obstructive hydrocephalus is characterized by an increase in intracranial pressure due to blockage in the CSF circulation pathway.

**Why the Correct Answer is Right:**

The correct answer, **B. Post-haemorrhagic hydrocephalus**, is the most common cause of obstructive hydrocephalus among children. Post-haemorrhagic hydrocephalus occurs due to the blockage in the CSF circulation pathway following a parenchymal haemorrhage, such as that seen in a subdural or intracerebral haemorrhage. Haemorrhage can lead to inflammation, scarring, and obstruction of the CSF pathways, causing obstructive hydrocephalus.

**Why Each Wrong Option is Incorrect:**

A. **Fetal ventriculomegaly (A)** is a condition characterized by enlarged ventricles in utero, often a precursor to postnatal hydrocephalus. However, it does not address the blockage in the CSF circulation pathway, making it an incorrect answer to the question about obstructive hydrocephalus.

C. **Post-meningitic hydrocephalus (C)** is a complication of meningitis, where inflammation and infection can lead to obstruction of CSF pathways. However, the question specifically asks for the commonest cause among children, which is not met by post-meningitic hydrocephalus.

D. **Post-neuroblastoma hydrocephalus (D)** is a complication of neuroblastoma, a malignant tumor of the neural crest cells. Although it can lead to hydrocephalus due to obstruction in CSF pathways, it is less common compared to post-haemorrhagic hydrocephalus, making it an incorrect answer for this question.

**Clinical Pearls:**

1. Hydrocephalus is a syndrome characterized by the accumulation of cerebrospinal fluid (CSF) within the ventricles of the brain, leading to increased intracranial pressure and subsequent neurological impairment.
2. Obstructive hydrocephalus is a type of hydrocephalus that occurs when there is a blockage in the CSF circulation pathway.
3. In pediatric patients, post-haemorrhagic hydrocephalus is more common than post-meningitic hydrocephalus.
4. Although neuroblastoma can lead to hydrocephalus, it is less common compared to post-haemorrhagic hydrocephalus, making it an incorrect answer to this question.
5. Fetal ventriculomegaly (A) is a risk factor for postnatal hydrocephalus but does not address the blockage in CS