**Core Concept**
Neuroangiofibroma, also known as juvenile nasopharyngeal angiofibroma (JNA), is a rare, benign tumor that arises from the nasopharynx. It is characterized by its rich vascular supply and potential for aggressive growth, often leading to nasal obstruction and epistaxis. The tumor is more common in adolescent males.

**Why the Correct Answer is Right**
The investigation of choice for neuroangiofibroma is a **selective arterial angiography**. This is because JNA is highly vascularized, and selective arterial angiography allows for precise visualization of the tumor's blood supply. The procedure involves injecting a contrast agent into the arteries that supply the tumor, enabling the radiologist to identify the areas of blood flow and potential sites for embolization or surgical resection. The angiogram can also help differentiate JNA from other nasopharyngeal masses.

**Why Each Wrong Option is Incorrect**
**Option A:** CT scan with contrast - While a CT scan with contrast can provide valuable information about the tumor's size and location, it is not the investigation of choice for neuroangiofibroma due to its limited ability to visualize the tumor's blood supply.

**Option B:** MRI - MRI is not typically used as the primary investigation for neuroangiofibroma, as it may not provide sufficient detail about the tumor's vascular supply.

**Option C:** Plain X-ray - Plain X-ray is not sufficient for diagnosing neuroangiofibroma, as it may not reveal the tumor's presence or extent.

**Clinical Pearl / High-Yield Fact**
It is essential to consider neuroangiofibroma in the differential diagnosis of adolescent males presenting with nasal obstruction, recurrent epistaxis, or other symptoms related to the nasopharynx.

**Correct Answer:** C. Selective arterial angiography.