**Core Concept:** Trigeminal Autonomic Cephalgia (TAC) is a group of primary headache disorders characterized by both ocular and facial autonomic symptoms along with headache. The three subtypes are:

1. TAC1: Atypical ophthalmic headache (Lesser occipital neuralgia, ophthalmic branch of trigeminal nerve pain)
2. TAC2: Hemicrania continua (persistent unilateral headache with autonomic symptoms)
3. TAC3: Sinus headache (sinusitis-induced headache with autonomic symptoms)

**Why the Correct Answer is Right:**

The correct answer is D (TAC3 is a sinus headache) because TAC3 is a subtype of trigeminal autonomic cephalgia where the headache is primarily caused by underlying sinusitis. The headache is unilateral and is often accompanied by autonomic symptoms like nasal congestion, rhinorrhea, conjunctival injection, and facial swelling.

**Why Each Wrong Option is Incorrect:**

A. This option refers to TAC1 (lesser occipital neuralgia) which is a subtype of TAC characterized by unilateral headache and autonomic symptoms from the lesser occipital nerve. This is different from TAC3.

B. TAC2 (hemicrania continua) is a subtype of TAC characterized by persistent unilateral headache with autonomic symptoms. It is not related to sinusitis, making it incorrect in this context.

C. TAC3 is not a sinus headache, but a subtype of TAC characterized by sinusitis-induced headache with autonomic symptoms.

**Clinical Pearl:**

Understanding the different subtypes of trigeminal autonomic cephalgias is essential for proper diagnosis and management of these conditions. TAC3 (sinus headache) is a headache caused by underlying sinusitis and can be confused with migraine or tension headache. A thorough history and physical examination, including sinus evaluation, is crucial in differentiating these conditions.

**Correct Answer:**

Correct Answer: D (TAC3 is a sinus headache)

**Why Each Wrong Option is Incorrect:**

A. Correct Answer: TAC1 is lesser occipital neuralgia, which is a different headache disorder characterized by unilateral headache and autonomic symptoms from the lesser occipital nerve.

B. Correct Answer: TAC2 is hemicrania continua, a different subtype of TAC characterized by persistent unilateral headache with autonomic symptoms. It is not related to sinusitis.

C. Correct Answer: TAC3 is a sinus headache caused by sinusitis, not migraine or tension headache, making it a distinct headache type.