Giant cell arteritis (GCA) is a granulomatous vasculitis affecting large and medium-sized arteries in individuals over 50 years of age. The temporal artery is the most commonly affected vessel, and it can lead to permanent vision loss through anterior ischemic optic neuropathy (AION). The aorta and its major branches (subclavian, axillary, carotid, vertebral arteries) may also be involved. It shows 40-60% association with polymyalgia rheumatica (PMR). Rapid diagnosis can be made with temporal artery ultrasound halo sign. CT/MR angiography is used to evaluate aortic involvement. PET-CT has high sensitivity for demonstrating active vascular inflammation. High-dose corticosteroid therapy must be started urgently — time is critical to prevent vision loss.
Age Range
50-90
Peak Age
70
Gender
Female predominant
Prevalence
Uncommon
GCA is a T-cell-mediated granulomatous inflammation starting from vasa vasorum in the adventitia of large arteries. Dendritic cells become activated in the arterial wall and recruit CD4+ T-cells. These T-cells secrete IFN-γ and IL-17 → macrophage activation and giant cell formation → granuloma formation. Intimal hyperplasia, medial smooth muscle damage, and elastic fiber fragmentation occur. Intimal hyperplasia leads to luminal narrowing → ischemic complications (vision loss, stroke, extremity claudication). Medial damage predisposes to aneurysm formation — particularly thoracic aortic aneurysm is a late complication of GCA. On imaging, arterial wall edema and enhancement reflect increased vascular permeability in the media and adventitia from active granulomatous inflammation. The 'halo sign' on ultrasonography represents the concentric hypoechoic edema band in the arterial wall — this edema is extravascular fluid accumulation caused by T-cell infiltration and granulomatous inflammation.
Concentric, homogeneous, hypoechoic wall thickening surrounding the arterial lumen on temporal artery ultrasound. Reflects arterial wall thickening due to granulomatous inflammation and edema. Considered pathognomonic for GCA (specificity 96%). Rapidly disappears after treatment initiation — therefore pre-treatment imaging is critically important. Included as a high-weight diagnostic criterion in EULAR/ACR 2018 classification criteria.
Concentric, homogeneous, hypoechoic wall thickening surrounding the arterial lumen on temporal artery B-mode ultrasound ('halo sign'). Halo thickness is usually between 0.3-1.0 mm. Does not compress with probe pressure (firm edema). Bilateral and symmetric involvement is typical but may be asymmetric. Frontal and parietal branches of the temporal artery should be evaluated separately. Halo sign should also be sought in axillary and carotid arteries. Sensitivity of halo sign is 77%, specificity is 96%. Disappears 2-4 weeks after treatment initiation — therefore pre-treatment imaging is important.
Report Sentence
Concentric hypoechoic wall thickening surrounding the lumen (halo sign) is observed on temporal artery ultrasound, consistent with giant cell arteritis; urgent corticosteroid therapy should be considered.
Concentric wall thickening and mural enhancement of aorta, subclavian, axillary, and carotid arteries on CT angiography. Wall thickness is usually 2-4 mm. Enhancement is prominent between inner layer (intima) and outer layer (adventitia) — double ring pattern. Luminal narrowing may be focal or diffuse. Subclavian/axillary artery involvement is highly typical for GCA and important in differentiation from atherosclerosis. In aortic involvement, wall thickening is homogeneous and concentric — atherosclerosis shows eccentric plaque.
Report Sentence
Concentric wall thickening and mural enhancement of bilateral axillary/subclavian arteries on CT angiography, consistent with large vessel vasculitis (giant cell arteritis).
Concentric mural enhancement on T1 contrast-enhanced sequences and wall edema (hyperintensity) on T2/STIR sequences of temporal artery or large vessel walls on high-resolution MRI. Black-blood MR technique clearly images arterial wall pathology by suppressing blood flow signal. 3T MRI is superior to 1.5T in demonstrating temporal artery wall thickening (<1 mm). Wall edema appears as bright signal on STIR/T2 fat-sat sequences. Prominent mural enhancement on contrast T1 due to vasa vasorum activation. MRI is also useful for monitoring residual inflammation after steroid therapy.
Report Sentence
Hyperintense edema on T2/STIR and prominent mural enhancement on contrast T1 in the temporal/axillary artery wall on MRI, consistent with active giant cell arteritis.
Increased FDG uptake in the aorta and major branches (subclavian, axillary, carotid, femoral arteries) on FDG PET-CT — metabolic marker of vascular inflammation. Uptake pattern is typically diffuse, symmetric, and homogeneous. Aortic wall uptake higher than liver uptake (visual grade ≥2 or SUVmax >2.0) is considered significant. PET-CT is more sensitive than CT/MR in detecting subclinical aortic involvement (sensitivity 80-90%, specificity 89-98%). Also used for monitoring treatment response — FDG uptake decreases with successful treatment.
Report Sentence
Increased diffuse FDG uptake above liver level in the aorta and axillary/subclavian arteries on PET-CT, consistent with active large vessel vasculitis (giant cell arteritis).
Focal or long-segment stenosis/occlusion of subclavian, axillary, carotid, or vertebral arteries on CT angiography. Stenosis is typically smooth-contoured and concentric — different from atherosclerotic irregular narrowing. In occlusion, collateral circulation develops (especially upper extremity arcade). Bilateral axillary artery stenosis is highly typical for GCA. Stenosis/occlusion reflects chronic luminal narrowing due to intimal hyperplasia. Subclavian steal phenomenon may develop — producing vertebrobasilar symptoms.
Report Sentence
Smooth-contoured concentric stenosis of bilateral axillary arteries and development of collateral circulation on CT angiography, consistent with chronic giant cell arteritis.
Thoracic aortic aneurysm or dilation developing in the setting of GCA — 17-fold increased risk compared to normal population in GCA patients. Aneurysm typically located in ascending aorta or aortic arch. CT shows fusiform aortic dilation with wall thickening. Dissection or rupture may develop as complications. May appear years after GCA diagnosis (average 5-7 years) — therefore long-term aortic surveillance is required. Intramural hematoma or calcified wall thickening on non-contrast CT may be a clue.
Report Sentence
Fusiform dilation and concentric wall thickening of the thoracic aorta are observed, suggesting aortic aneurysm developing in the setting of GCA; regular diameter surveillance is recommended.
Criteria
Primary temporal artery involvement. Temporal headache, jaw claudication, scalp tenderness, visual disturbances. Temporal artery pulse diminished or absent.
Distinct Features
US halo sign in temporal artery is pathognomonic. High AION risk — requires urgent steroids. Temporal artery biopsy is gold standard. ESR usually >50 mm/hour.
Criteria
Involvement of aorta and primary branches (subclavian, axillary, carotid, vertebral, renal, iliac arteries). Temporal artery involvement may or may not coexist. Extremity claudication, asymmetric blood pressure, bruit findings.
Distinct Features
Diagnosis with CT/MR angiography and PET-CT. Temporal artery biopsy may be negative. 17-fold increased risk of aortic aneurysm. Requires long-term aortic surveillance.
Criteria
GCA developing in the setting of polymyalgia rheumatica (proximal muscle pain and stiffness). GCA develops in 15-20% of PMR patients. PMR accompanies 40-60% of GCA patients.
Distinct Features
PMR symptoms may start before, after, or simultaneously with GCA. Urgent GCA evaluation is needed if visual complaints or new headache develop in PMR patients. FDG PET-CT may show both bursitis and vascular involvement in both conditions.
Distinguishing Feature
Takayasu arteritis occurs in women <40 years while GCA occurs in individuals >50 years. Both are large vessel vasculitides affecting aorta and branches. Aortic wall thickening is more prominent in Takayasu (>4 mm) and pulmonary artery involvement may occur; temporal artery involvement is distinguishing in GCA. Geographic distribution also differs: Takayasu is more common in Asia, GCA in Northern European/Scandinavian populations.
Distinguishing Feature
FMD affects medium-sized arteries with string of beads pattern; GCA affects large arteries with concentric wall thickening. FMD has no inflammation markers (normal ESR/CRP); GCA has prominent inflammation (elevated ESR/CRP). FMD occurs in young women, GCA in elderly individuals. FMD has no wall enhancement.
Distinguishing Feature
Atherosclerotic aortopathy shows irregular intimal calcification and eccentric plaque; GCA shows concentric homogeneous wall thickening. Atherosclerosis typically involves infrarenal aorta; GCA prefers ascending aorta and arch. Inflammatory markers are usually normal in atherosclerosis; markedly elevated in GCA.
Distinguishing Feature
IgG4-related aortitis/periaortitis also shows aortic wall thickening but periaortic soft tissue ('mantle sign') is typical — GCA has no periaortic soft tissue. IgG4 disease is accompanied by elevated serum IgG4 and multiple organ involvement (pancreas, salivary glands, retroperitoneum); elevated ESR/CRP and PMR association are distinguishing in GCA.
Urgency
emergentManagement
medicalBiopsy
NeededFollow-up
3-monthThe most important time-sensitive complication in GCA diagnosis is anterior ischemic optic neuropathy (AION) — leads to permanent blindness if untreated. In GCA suspicion, high-dose corticosteroid (prednisolone 1 mg/kg/day or IV methylprednisolone pulse) should be started IMMEDIATELY without waiting for biopsy results. Temporal artery biopsy should be performed within 2 weeks (steroids do not affect biopsy results). US halo sign provides rapid alternative diagnosis to biopsy. CT/MR angiography or PET-CT should be performed to evaluate large vessel involvement. Steroid tapering should be slow (12-24 months); tocilizumab (IL-6 blocker) is used in steroid-dependent/resistant cases. Annual CT/MR aortic surveillance is recommended due to aortic aneurysm risk.
Treatment in GCA is urgent due to vision loss risk — high-dose corticosteroids must be started immediately (without waiting for biopsy result). Temporal artery biopsy is the gold standard but US halo sign can diagnose with high sensitivity. Chronic GCA carries increased risk of thoracic aortic aneurysm and dissection — annual CT follow-up is recommended.