**Core Concept**
Pseudotumor cerebri, also known as idiopathic intracranial hypertension (IIH), is a condition characterized by increased intracranial pressure in the absence of a space-occupying lesion or other identifiable cause. It is often associated with headache, visual disturbances, and papilledema.

**Why the Correct Answer is Right**
The correct answer, **B. Increased protein in CSF**, is incorrect because pseudotumor cerebri is typically associated with normal or low protein levels in cerebrospinal fluid (CSF). The pathophysiology of IIH involves impaired CSF absorption at the arachnoid granulations, leading to increased CSF pressure. However, this does not result in an increase in protein levels in the CSF. Instead, the protein levels in CSF are usually normal or even decreased in patients with pseudotumor cerebri.

**Why Each Wrong Option is Incorrect**
**Option A:** Normal-sized ventricles on CT scan is a characteristic feature of pseudotumor cerebri, as the condition is not associated with hydrocephalus or other structural abnormalities.

**Option C:** Papilledema is a common finding in pseudotumor cerebri, resulting from increased intracranial pressure.

**Option D:** Absence of focal neurological deficit is also a characteristic feature of pseudotumor cerebri, as the condition typically does not result in focal neurological deficits.

**Clinical Pearl / High-Yield Fact**
A key distinguishing feature of pseudotumor cerebri is the absence of a space-occupying lesion or other identifiable cause of increased intracranial pressure. This can be remembered using the mnemonic "Pseudotumor Cerebri: Painful, Papilledema, and Pressure without a Pathological Lesion".

**✓ Correct Answer: B. Increased protein in CSF**