Ultrasound in Giant Cell Arteritis: halo-sign and compression-sign of Temporal Arteries
Clinical and Ultrasound Context
Giant cell (temporal) arteritis is a vasculitis of large and medium-sized arteries in elderly patients (usually >50 years). The temporal arteries are affected (headache, tenderness, risk of vision loss), as well as the carotid, vertebral, and axillary arteries. Diagnosis and treatment are determined by a rheumatologist; disease activity is assessed by CEUS/PET and laboratory markers.
Halo sign
The characteristic ultrasound finding is the 'halo sign': a homogeneous hypoechoic (dark) concentric wall thickening, reflecting acute inflammation. In giant cell arteritis, the halo is visualized on the temporal artery, in contrast to the bright 'macaroni sign' in Takayasu arteritis.
Compression sign
The thickened inflamed wall does not collapse on compression with the transducer — compression sign is positive. This distinguishes inflammatory thickening from a compressible lumen and serves as an important differential criterion.
IMT Thickness Thresholds
To confirm diagnosis, intima-media complex (IMT) thickness thresholds are used (based on data informing EULAR):
| Artery | Thickness Threshold |
|---|---|
| Common carotid | approximately 0.7 mm (value ~1.2–1.3 mm provides nearly 100% specificity) |
| Axillary | approximately 1.0 mm |
| Temporal | tenths of a millimeter |
Multi-basin Examination and Differential Diagnosis
Examine multiple vascular beds (cranial + extracranial). Differentiate by echogenicity, age, and vessel caliber: giant cell arteritis — elderly, temporal artery, dark hypoechoic halo, positive compression sign; Takayasu arteritis — young, large vessels (common carotid, subclavian), bright 'macaroni sign'. Remember false-positive results in atherosclerosis.
Frequently asked questions
What is a positive compression sign?
The thickened inflamed wall of the temporal artery does not collapse on compression with the transducer — this is a positive compression sign, reflecting inflammatory thickening.
What does the halo sign look like?
A homogeneous hypoechoic (dark) concentric wall thickening of the artery, reflecting acute inflammation.
What IMT thresholds are used?
According to data informing EULAR: common carotid — approximately 0.7 mm (~1.2–1.3 mm provides nearly 100% specificity), axillary — approximately 1.0 mm, temporal — tenths of a millimeter.
How do you differentiate GCA from Takayasu arteritis?
GCA — elderly, temporal artery, dark hypoechoic halo, positive compression sign; Takayasu arteritis — young, large vessels (common carotid, subclavian), bright 'macaroni sign'.
What are sources of false-positive results?
Atherosclerosis can produce false-positive results; according to sources, positive halo sign has also been described in amyloidosis of temporal arteries.