**Communicating Hydrocephalus**

**Core Concept**
Communicating hydrocephalus refers to the accumulation of cerebrospinal fluid (CSF) in the brain due to an obstruction or disruption in the normal flow of CSF from the ventricles to the subarachnoid space, but with no blockage at the level of the ventricles or the fourth ventricle.

**Why the Correct Answer is Right**
In communicating hydrocephalus, the obstruction or disruption in CSF flow is typically located at the level of the arachnoid granulations or the arachnoid villi, which are responsible for reabsorbing CSF into the bloodstream. This can be due to various factors such as subarachnoid hemorrhage, infection, or inflammation, leading to scarring and obstruction of the arachnoid granulations. As a result, CSF accumulates in the ventricles, leading to increased intracranial pressure and hydrocephalus.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because non-communicating hydrocephalus refers to a blockage at the level of the ventricles or the fourth ventricle, leading to a failure of CSF circulation and accumulation of CSF in the ventricles.
**Option B:** This option is incorrect because normal pressure hydrocephalus (NPH) is a type of communicating hydrocephalus, but it is characterized by a specific set of symptoms, including gait disturbances, dementia, and urinary incontinence, which are not mentioned here.
**Option C:** This option is incorrect because obstructive hydrocephalus refers to a blockage at the level of the ventricles or the fourth ventricle, leading to a failure of CSF circulation and accumulation of CSF in the ventricles.

**Clinical Pearl / High-Yield Fact**
Communicating hydrocephalus often presents with symptoms such as headache, nausea, and vomiting, and may be associated with increased intracranial pressure. It is essential to differentiate communicating hydrocephalus from non-communicating hydrocephalus and normal pressure hydrocephalus, as the management and treatment of these conditions may differ.

**Correct Answer: C. Obstructive hydrocephalus is not the same as communicating hydrocephalus.