From the Guidelines
Ultrasound of temporal and axillary arteries should be considered as the first imaging modality to investigate mural inflammatory changes in patients with suspected giant cell arteritis (GCA). This recommendation is based on the most recent and highest quality study, which suggests that ultrasound is a valuable tool for detecting characteristic findings such as a "halo sign" (vessel wall edema), stenosis, or occlusions of the temporal arteries 1.
Key Imaging Modalities for GCA
- Ultrasound: first-line imaging modality for evaluating suspected GCA, particularly for temporal and axillary arteries
- High-resolution MRI or FDG-PET: alternative imaging modalities for assessing cranial arteries in patients with suspected GCA
- FDG-PET, MRI, or CT: can be used for detecting mural inflammation or luminal changes of extracranial arteries in patients with suspected GCA
Timing of Imaging
Imaging studies should be performed promptly, ideally before or within 72 hours of starting corticosteroid therapy, as treatment can rapidly reduce inflammatory changes and decrease diagnostic sensitivity 1. However, imaging should not delay initiation of treatment when clinical suspicion is high.
Importance of Rapid Access to Imaging
The task force urged rapid access to diagnostic imaging tests, commensurate with fast-track clinics for patients with suspected GCA, to minimize the risk of blindness and other ischemic manifestations 1.
Complementary Diagnostic Tools
Imaging studies complement clinical assessment and laboratory findings (elevated ESR/CRP) in the diagnostic workup of temporal arteritis, and temporal artery biopsy remains the gold standard for definitive diagnosis, showing characteristic granulomatous inflammation with giant cells 1.
From the Research
Imaging for Giant Cell Arteritis (GCA) Evaluation
The following imaging modalities are used for the evaluation of GCA:
- Color Doppler Ultrasound of temporal arteries: This is a non-invasive diagnostic tool that has been proven to be powerful in diagnosing GCA 2, 3, 4, 5, 6.
- Temporal artery biopsy (TAB): Although still considered a gold standard for diagnosis, TAB is often used as a secondary test after ultrasound evaluation 2, 3.
- Other imaging tests: Physician-diagnosed GCA based on clinical findings and other imaging tests can also be used to confirm the diagnosis 2.
Specific Imaging Techniques
- Bilateral temporal halo signs seen on ultrasound are considered positive for GCA diagnosis 2.
- Colour Doppler ultrasound examination has been proposed as a useful diagnostic screening tool in cases of GCA suspicion 3.
- Automated image analysis tools, such as those using artificial intelligence algorithms, can aid in the diagnosis of GCA by detecting the halo sign on CDU images 4.
- Doppler ultrasound of the temporal arteries has a sensitivity and specificity reaching 69% and 82%, respectively, making it a first-line diagnostic tool in GCA 6.