Which of the following is not a cause of communicating hydrocephalus?
**Communicating Hydrocephalus**
**Core Concept**
Communicating hydrocephalus is a condition characterized by an accumulation of cerebrospinal fluid (CSF) in the brain due to impaired CSF absorption, leading to increased intracranial pressure. This type of hydrocephalus is often associated with normal or enlarged ventricles.
**Why the Correct Answer is Right**
Communicating hydrocephalus typically occurs due to blockage of the CSF pathways, such as the arachnoid granulations or the subarachnoid space, or due to impaired CSF reabsorption. This can be caused by conditions like meningitis, subarachnoid hemorrhage, or tumors. The correct answer is the option that does not involve a blockage or impairment of CSF pathways.
**Why Each Wrong Option is Incorrect**
**Option A:** Blockage of the aqueduct of Sylvius can cause non-communicating (obstructive) hydrocephalus, not communicating hydrocephalus.
**Option B:** Infection or inflammation of the subarachnoid space, such as meningitis, can lead to communicating hydrocephalus by blocking the arachnoid granulations.
**Option C:** Subarachnoid hemorrhage can cause communicating hydrocephalus by blocking the subarachnoid space and impairing CSF reabsorption.
**Clinical Pearl / High-Yield Fact**
In communicating hydrocephalus, the CSF pressure is typically elevated, but the ventricles may be normal or enlarged, distinguishing it from non-communicating (obstructive) hydrocephalus.
**Correct Answer:** A. Blockage of the aqueduct of Sylvius can cause non-communicating (obstructive) hydrocephalus, not communicating hydrocephalus.