**Core Concept:**
The question is asking about the possible pathways through which a central nervous system (CNS) infection can spread. The CNS includes the brain and spinal cord, and infections involving these areas can have severe consequences. Understanding the routes of infection is crucial for appropriate diagnosis and treatment.

**Why the Correct Answer is Right:**
CNS infections can spread via several routes, including bloodstream, meningeal spaces, cerebrospinal fluid (CSF), and direct extension. In this case, the correct answer is **D** - **Bloodstream**. Infection of other organs or tissues can spread to the CNS via the bloodstream, involving the meningeal spaces, CSF, or direct extension.

**Why Each Wrong Option is Incorrect:**

**A.** **Meningeal spaces:** While meningeal spaces are involved in meningitis, they are not the primary route of infection for most CNS infections.

**B.** **Cerebrospinal fluid (CSF):** While CSF plays a role in CNS infections, it is not the sole route for infection to reach the CNS.

**C.** **Direct extension:** Direct extension refers to the spread of infection from an adjacent site (e.g., brain abscess from a contiguous focus), but it is not the primary route of infection for most CNS infections.

**Clinical Pearl / High-Yield Fact:**
Understanding the routes of CNS infections helps in formulating a proper differential diagnosis and treatment plan. CNS infections can be caused by bacteria, viruses, fungi, or parasites. Early recognition and appropriate treatment are crucial to prevent complications and improve outcomes.

**Correct Answer:** D. Bloodstream