**Question:** A 16-year-old boy with no prior medical problems has complained of headaches for the past 9 months. There are no abnormal findings on physical examination. CT scan of the head shows an enlargement of the lateral cerebral ventricles and third ventricle. A lumbar puncture is performed with normal opening pressure, and clear CSF is obtained, which has a slightly elevated protein, normal glucose, and no leukocytes. Which of the following intracranial lesions is most likely to cause these findings?

A. Hydrocephalus
B. Encephalitis
C. Subarachnoid hemorrhage
D. Subdural hematoma

**Core Concept:**

The clinical scenario presented describes a patient who presents with a history of progressive headaches and imaging findings of enlarged ventricles on CT scan, which is consistent with increased intracranial pressure and cerebrospinal fluid (CSF) analysis showing slightly elevated protein and normal glucose levels without leukocytes, which is also characteristic of increased intracranial pressure.

**Why the Correct Answer is A - Hydrocephalus:**

Hydrocephalus is a condition characterized by the accumulation of excess cerebrospinal fluid (CSF) within the ventricular system of the brain, leading to ventricular enlargement. This condition results in increased intracranial pressure and the clinical symptoms described, including progressive headaches. CSF analysis in hydrocephalus typically shows elevated protein levels and normal glucose levels without leukocytes, similar to the findings in the given case.

**Why the other options are incorrect:**

**Option B - Encephalitis:** Encephalitis refers to inflammation of the brain due to an infection, autoimmune response or other causes. Encephalitis is unlikely in this scenario because it presents with a more acute onset of neurological symptoms and signs, which are not consistent with the progressive headaches described in the case. Additionally, encephalitis usually shows elevated protein levels and glucose levels with or without leukocytes in CSF analysis.

**Option C - Subarachnoid hemorrhage:** Subarachnoid hemorrhage refers to bleeding in the subarachnoid space, which is the space between the inner and outer layers of the brain. This condition presents with acute neurological symptoms and signs, not the progressive headaches described in the case. Moreover, subarachnoid hemorrhage often shows elevated protein levels and glucose levels with leukocytosis in CSF analysis.

**Option D - Subdural hematoma:** Subdural hematoma is a type of intracranial hemorrhage involving the subdural space, which is between the dura mater and the arachnoid mater. This condition presents with acute neurological symptoms and signs, not the progressive headaches described in the case. Additionally, subdural hematoma typically shows elevated protein levels and glucose levels with leukocytosis in CSF analysis.

**Core Concept:** The correct answer, Hydrocephalus, is a medical condition characterized by the accumulation of cerebrospinal fluid (CSF) within the ventricular system of the brain, leading to increased intracranial pressure. This condition presents with progressive headaches, which is consistent with the described symptoms in the case. Additionally, elevated protein levels and normal glucose levels with elevated total cell count (leukocytosis) in