**Core Concept**
Cryptococcal meningitis is a serious fungal infection that affects the central nervous system. The most common fungus to cause meningitis in immunocompromised patients, particularly those with HIV/AIDS, is Cryptococcus neoformans.

**Why the Correct Answer is Right**
Cryptococcus neoformans is a type of encapsulated yeast that is commonly found in soil contaminated with pigeon droppings. It enters the body through inhalation of spores and can cause meningitis in individuals with weakened immune systems. The infection occurs when the yeast crosses the blood-brain barrier and invades the meninges, leading to inflammation and damage to the central nervous system. The capsule of Cryptococcus neoformans is composed of polysaccharides, which helps the fungus evade the host's immune response.

**Why Each Wrong Option is Incorrect**
* **Option A:** Aspergillus species can cause invasive aspergillosis, which affects the lungs, brain, and other organs in immunocompromised patients. However, Aspergillus is not the most common fungus to cause meningitis.
* **Option B:** Histoplasma capsulatum can cause histoplasmosis, which primarily affects the lungs and can disseminate to other organs in immunocompromised patients. While it can cause meningitis, it is not the most common fungus to do so.
* **Option D:** Candida species are common causes of fungal infections in humans, but they are not typically associated with meningitis.

**Clinical Pearl / High-Yield Fact**
Cryptococcal meningitis is a medical emergency that requires prompt treatment with antifungal medications, such as amphotericin B and fluconazole. Early diagnosis and treatment are critical to prevent complications and improve outcomes.

**Correct Answer:** C. Cryptococcus neoformans