A 58-year-old man presents with sudden onset of severe headache, jaw claudication, and visual disturbances. Temporal artery biopsy shows granulomatous inflammation with giant cells. What is the most common site of vascular involvement in this condition?

Explanation

## Giant Cell Arteritis: Vascular Distribution **Key Point:** Giant cell arteritis (temporal arteritis) predominantly affects large and medium-sized elastic arteries, with the temporal and other cranial arteries being the most commonly and severely involved sites. ### Pathophysiology Giant cell arteritis is a granulomatous vasculitis of large and medium elastic arteries. The inflammation preferentially targets: - **Temporal arteries** (most common and clinically significant) - **Ophthalmic arteries** (leading to vision loss) - **Posterior ciliary arteries** (anterior ischemic optic neuropathy) - Other cranial branches of the external carotid system ### Clinical Correlations | Site of Involvement | Clinical Manifestation | Frequency | | --- | --- | --- | | Temporal artery | Headache, scalp tenderness, jaw claudication | Most common | | Ophthalmic artery | Amaurosis fugax, permanent vision loss | 15–20% | | Posterior ciliary | Anterior ischemic optic neuropathy (AION) | Common cause of blindness | | Aorta and branches | Aortic aneurysm, dissection | 10–15% | | Coronary arteries | MI (rare) | <5% | | Mesenteric arteries | Mesenteric ischemia (rare) | <5% | **High-Yield:** The temporal artery is the hallmark site — biopsy showing granulomatous inflammation with giant cells and fragmentation of the internal elastic lamina is diagnostic. Cranial artery involvement explains the classic triad of headache, visual symptoms, and jaw claudication. **Clinical Pearl:** Although systemic inflammation can affect the aorta and its major branches (aortic arch syndrome), the temporal and cranial arteries remain the most frequently and severely involved, making them the diagnostic and clinical focus. **Warning:** Do not confuse with Takayasu arteritis, which affects the aorta and its proximal branches in younger patients (typically women <40 years). ### Why Temporal Arteries? The predilection for cranial arteries in GCA is thought to relate to: - Elastic fiber composition of these vessels - Local immune response to elastic fiber breakdown - Age-related changes in arterial wall immunity [cite:Harrison 21e Ch 378]