A 48-year-old man with AIDS is admitted to the hospital with a fever of 38.7degC (103degF), persistent cough, and diarrhea. His CD4 cell count is less than 500/mL. The patient is started on broad-spectrum antibiotics. He has also experienced a recent decline in cognitive function. He is at increased risk of developing which of the following CNS neoplasms?

**Core Concept**
The question is testing the patient's risk of developing a specific CNS neoplasm due to his immunocompromised state, specifically with a CD4 cell count below 500/mL. This is related to the increased susceptibility to opportunistic infections and malignancies in HIV/AIDS patients.

**Why the Correct Answer is Right**
The patient is at increased risk of developing primary CNS lymphoma (PCNSL), a type of non-Hodgkin's lymphoma that originates in the brain. This is due to the compromised immune system, which fails to control EBV (Epstein-Barr virus) reactivation, leading to malignant transformation of B lymphocytes. PCNSL is a common CNS neoplasm in HIV/AIDS patients, particularly those with low CD4 counts.

**Why Each Wrong Option is Incorrect**
**Option A:** Oligodendroglioma - This is a type of glioma that is not typically associated with HIV/AIDS.
**Option B:** Meningioma - While meningiomas can occur in HIV/AIDS patients, they are not as strongly associated with the disease as PCNSL.
**Option C:** Glioblastoma - This is a type of glioma that is more commonly seen in immunocompetent individuals.

**Clinical Pearl / High-Yield Fact**
In HIV/AIDS patients, a low CD4 count (<200/mL) increases the risk of PCNSL, and symptoms such as cognitive decline, seizures, and focal neurological deficits may be the presenting features of this malignancy. **Correct Answer:** C.

✓ Correct Answer: C. Lymphoma