## **Core Concept**
The question tests the understanding of referred pain in the context of a peritonsillar abscess. Referred pain occurs when pain is perceived at a location other than the site of the painful stimulus. This phenomenon is due to the convergence of afferent nerve fibers from different areas onto the same spinal neuron.

## **Why the Correct Answer is Right**
The correct answer, **D. Common nerve supply**, is right because the pain in a peritonsillar abscess is referred to the ear due to the common nerve supply. The tonsils and the ear share a common innervation through the **trigeminal nerve** (cranial nerve V) and the **glossopharyngeal nerve** (cranial nerve IX). The glossopharyngeal nerve provides sensory innervation to the tonsils and also to the middle ear through the tympanic branch (Jacobson's nerve). This shared innervation leads to the referred pain in the ear when there is inflammation or an abscess in the peritonsillar area.

## **Why Each Wrong Option is Incorrect**
- **Option A: Direct spread of infection** is incorrect because while direct spread of infection can cause complications, it does not explain the referred pain to the ear.
- **Option B: Increased intracranial pressure** is incorrect as it is not directly related to the mechanism of referred pain in peritonsillar abscess.
- **Option C: Referred pain via the vagus nerve** is incorrect because, although the vagus nerve does provide some innervation to the throat, the specific referral of pain from the peritonsillar area to the ear is primarily due to the glossopharyngeal nerve.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **glossopharyngeal nerve** plays a crucial role in the referred pain pathway from the tonsillar area to the ear. This is a classic example of referred pain and is important for clinical diagnosis and management.

## **Correct Answer: D. Common nerve supply**