**Core Concept**
Pheochromocytomas are catecholamine-secreting tumors that can arise from the adrenal glands or, less commonly, from extra-adrenal sites, such as the sympathetic chain. The evaluation of these tumors requires imaging modalities that can accurately detect and characterize their location, size, and metabolic activity.

**Why the Correct Answer is Right**
MIBG (Metaiodobenzylguanidine) scintigraphy is a highly sensitive imaging modality for detecting extra-adrenal pheochromocytomas. MIBG is a catecholamine analog that accumulates in cells of the sympathetic nervous system, including pheochromocytomas. This allows for the detection of these tumors using a gamma camera. The sensitivity of MIBG scintigraphy for extra-adrenal pheochromocytomas is higher than other imaging modalities, such as CT or MRI, due to the specific uptake of MIBG by these tumor cells.

**Why Each Wrong Option is Incorrect**
**Option A:** CT (Computed Tomography) is a useful imaging modality for detecting adrenal pheochromocytomas but is less sensitive for extra-adrenal sites. CT may not accurately detect small or metastatic tumors.

**Option B:** MRI (Magnetic Resonance Imaging) is a sensitive imaging modality for detecting adrenal pheochromocytomas but is not as sensitive as MIBG scintigraphy for extra-adrenal sites. MRI may not accurately detect small or metastatic tumors.

**Option D:** PET (Positron Emission Tomography) is a highly sensitive imaging modality for detecting various tumors but is not as specific as MIBG scintigraphy for pheochromocytomas. PET may detect other tumors or inflammatory processes that are not pheochromocytomas.

**Clinical Pearl / High-Yield Fact**
MIBG scintigraphy is a sensitive imaging modality for detecting extra-adrenal pheochromocytomas due to its specific uptake by these tumor cells. This is a critical consideration in the evaluation of patients with suspected pheochromocytoma, particularly when the tumor is located outside the adrenal glands.

**Correct Answer:** C. MIBG scintigraphy.