A 68-year-old man presents with sudden onset of severe headache, jaw claudication, and visual disturbances. Temporal artery biopsy shows granulomatous inflammation with giant cells. Which is the most common site of vascular involvement in this condition?

Explanation

## Giant Cell (Temporal) Arteritis: Vascular Involvement Pattern **Key Point:** Giant cell arteritis (GCA) is a large-vessel vasculitis that predominantly affects the extracranial branches of the carotid artery, particularly the temporal artery, though it can involve other branches including occipital, ophthalmic, and posterior ciliary arteries. ### Pathological Features The disease is characterized by: - Granulomatous inflammation of the media and intima - Giant cells and epithelioid histiocytes - Fragmentation of the internal elastic lamina - Predominantly affects arteries of medium to large caliber ### Distribution of Vascular Involvement | Vessel Site | Frequency | Clinical Significance | |---|---|---| | Temporal artery | >90% | Diagnostic biopsy site; presents with headache, scalp tenderness | | Occipital artery | Common | Occipital headache | | Ophthalmic/posterior ciliary | Common | Amaurosis fugax, vision loss | | Coronary arteries | ~10% | Rare; can cause MI | | Aorta/aortic arch | ~15% | Late complication; aortic regurgitation, aneurysm | | Mesenteric arteries | <5% | Uncommon; mesenteric ischemia rare | **High-Yield:** The temporal artery is the **diagnostic gold standard** — biopsy showing granulomatous inflammation confirms GCA. However, the disease affects a spectrum of extracranial carotid branches, not just the temporal artery alone. ### Clinical Correlation - **Jaw claudication** = involvement of facial/maxillary arteries (branches of external carotid) - **Vision loss** = involvement of ophthalmic and posterior ciliary arteries (branches of internal carotid) - **Headache** = temporal and occipital artery involvement **Clinical Pearl:** Aortic involvement (aortic arch syndrome) occurs in ~15% of GCA patients, typically as a late complication, and can present with aortic regurgitation or thoracic aortic aneurysm. This is why long-term follow-up imaging is important. **Warning:** Do not confuse GCA with Takayasu arteritis (which affects the aorta and its proximal branches in young women) or polyarteritis nodosa (which spares the temporal arteries and typically affects medium-sized muscular arteries).