Large-Vessel Vasculitis: Multimodality Imaging Essentials

A practical radiology review of Large-Vessel Vasculitis: Multimodality Imaging Essentials, focused on imaging findings, differential diagnosis, reporting points, and high-yield teaching pearls.

Big Picture

• Imaging = cornerstone of diagnosis (often replaces biopsy).
• Multimodality approach (US + CTA/MRA + PET) is essential.
• Inflammation ≠ stenosis → functional changes can precede anatomy.
• Labs and symptoms are nonspecific → imaging drives decisions.

Core Entities

Giant Cell Arteritis (GCA): age > 50, female > male, cranial ± extracranial, risk = visual loss, stroke.

• Takayasu Arteritis (TA): age < 40, female ≫ male, aorta and branches, risk = stenosis, occlusion, aneurysm, silent CAD.
• Guideline Pearls
• EULAR: US first line for GCA, MRI/MRA first line for TA, imaging can replace biopsy.
• ACR: temporal artery biopsy still favored (US operator dependent).
• Catheter angiography → obsolete and unsafe.
• Ultrasound (US) — HIGH YIELD SIGNS
• Halo sign → hypoechoic wall edema in GCA.
• Compression sign → thickened wall remains visible.
• Macaroni sign → smooth hyperechoic circumferential wall in TA (chronic).
• Axillary arteries must be scanned in suspected GCA.
• IMT cutoffs: temporal ≤ 0.4 mm, vertebral ≤ 0.7 mm, carotid / subclavian / axillary ≤ 1.0 mm.

CTA — Classic Patterns

• Smooth concentric mural thickening (≈ 2–3 mm).
• Mural enhancement (> 20 HU on venous phase) = active inflammation.
• Double ring sign → TA (inflamed adventitia and media).
• Atherosclerosis = eccentric, irregular plaques.
• Radiation burden → limit in young TA patients.

MRI / MRA / VWI

• First line modality in TA.
• Black blood post contrast T1 weighted imaging = key sequence.

Differentiation: vasculitis → smooth concentric enhancement; atherosclerosis → eccentric plaque with lipid core.

• Cranial GCA clues: scalp dot sign on DWI, ophthalmic artery involvement.
• Enhancement ≠ active disease (fibrosis can enhance).

DWI — NEW AND TRENDY

• Non contrast marker of inflammation.
• “Scalp dot sign” in cranial GCA.
• Diagnostic performance approaching PET and contrast MRI (early data).
• Not yet standard

18F FDG PET/CT — FUNCTIONAL KING

• Detects vascular inflammation before anatomic wall thickening.
• Best used in FUO or when US and MRI are negative but suspicion remains high.

Visual grading versus liver uptake (exam classic): grade 0–1 negative, grade 2 equivocal, grade 3 positive.

• PETVAS score = global inflammatory burden (no validated cutoff).
• Pitfalls: atherosclerosis causes patchy uptake, post biopsy uptake is asymmetric.
• Treatment Response — TRICKY EXAM AREA
• Imaging changes lag behind clinical remission.
• Persistent wall thickening does not equal active disease.
• Persistent FDG uptake may reflect subclinical inflammation or vascular repair.
• Tocilizumab suppresses CRP → imaging becomes more important for activity assessment.

Differentiation

• GCA with PMR pattern on PET = strong diagnostic clue.
• TA characteristically spares temporal arteries.
• Behçet disease → aneurysms and thrombosis rather than mural thickening.
• IgG4 related disease → periaortitis with a soft tissue cuff.

Take Home MESSAGEs

• US for GCA, MRI for TA.
• Combine anatomic and functional imaging.
• FDG uptake can exist without stenosis.
• Do not equate enhancement with activity.
• Imaging drives diagnosis, staging, and complication detection.