**Core Concept**
The Spetzler-Main classification is a surgical grading system used to assess the risk of surgical intervention in cerebral arteriovenous malformations (AVMs) based on location and size. It evaluates three key features: depth of nidus, proximity to major vessels, and size of the AVM nidus.

**Why the Correct Answer is Right**
For a 5 cm nidus, the score is assigned based on size: up to 3 cm = 1 point, 3–5 cm = 2 points, and over 5 cm = 3 points. A 5 cm nidus falls into the 3–5 cm range, thus scoring **2 points**. This score is combined with other components (depth, vessel proximity), but the size component alone is key here. The classification helps predict surgical risk and guide treatment decisions.

**Why Each Wrong Option is Incorrect**
Option A: 3 – Incorrect because 3 cm or more is scored as 2 points, not 3. A 5 cm nidus is not yet in the "over 5 cm" category.
Option B: 4 – Incorrect; no component of Spetzler-Main assigns 4 points for size. This is outside the scoring scale.
Option D: 5 – Incorrect; the maximum score for size is 3, and 5 cm does not exceed the threshold for 3 points.

**Clinical Pearl / High-Yield Fact**
Remember the Spetzler-Main scoring: **Size (1–3 cm = 1, 3–5 cm = 2, >5 cm = 3)**, depth (1–3 points), and vessel proximity (1–3 points). A total score ≥ 5 indicates high surgical risk.

✓ Correct Answer: C. 2