What imaging modalities are used to diagnose giant cell arteritis in an older adult with a history of headaches, jaw claudication, or visual disturbances?

Imaging Modalities for Giant Cell Arteritis

Ultrasound of the temporal and axillary arteries should be considered the first-line imaging modality for diagnosing giant cell arteritis, showing a characteristic "halo sign" representing vessel wall inflammation. 1

Primary Imaging Approach

First-Line: Ultrasound

• Ultrasound of temporal and axillary arteries is the preferred initial imaging test when high expertise and prompt availability exist, as it can reliably replace temporal artery biopsy in appropriate clinical settings. 1, 2
• The "halo sign" (hypoechoic circumferential thickening around the arterial lumen) is the key diagnostic finding on ultrasound. 3, 2
• Ultrasound has the advantage of being non-invasive, readily available, and can be performed at the bedside without radiation exposure. 1

Alternative Cranial Artery Imaging

• High-resolution MRI or FDG-PET can serve as alternatives to ultrasound for assessing cranial arteries when ultrasound expertise is unavailable or results are inconclusive. 1
• However, MRI of cranial vessels currently has limited widespread validation and technical expertise in the US, which restricts its use as a replacement for temporal artery biopsy. 1

Large Vessel Imaging

Extracranial Vessel Assessment

• FDG-PET (commonly combined with low-dose CT) is the preferred modality for detecting large vessel involvement in the aorta and its major branches, showing increased tracer uptake in inflamed arterial walls. 1, 4
• MRI or CT angiography of the neck/chest/abdomen/pelvis can alternatively detect mural inflammation or luminal changes in extracranial arteries. 1
• Approximately 40% of GCA patients have aortic or branch vessel involvement, which may be asymptomatic at diagnosis but carries prognostic implications. 4

Clinical Context for Imaging Selection

When Temporal Artery Biopsy is Negative

• Noninvasive vascular imaging of large vessels should be performed with clinical assessment if temporal artery biopsy is negative but clinical suspicion remains high, as this may reveal extracranial GCA. 1, 3
• This approach is particularly important since GCA is a focal and segmental disease, and biopsy can miss affected segments. 3

Baseline Assessment

• Baseline noninvasive vascular imaging to evaluate large vessel involvement is recommended in all newly diagnosed GCA patients to detect aneurysms, stenoses, and guide subsequent monitoring. 3, 5

Imaging Modalities NOT Recommended

• Conventional angiography is not recommended for GCA diagnosis, as it has been superseded by the non-invasive imaging modalities described above. 1
• Conventional angiography only shows luminal changes and cannot detect vessel wall inflammation, which is the hallmark of active disease. 1

Key Diagnostic Findings by Modality

Ultrasound Findings

• Temporal artery thickening has a positive likelihood ratio of 4.70 for GCA diagnosis. 1, 5
• Loss of temporal artery pulse has a positive likelihood ratio of 3.25. 1, 5

Cross-Sectional Imaging Findings

• Circumferential arterial wall thickening on MRI or CT. 6
• Increased FDG uptake in arterial walls on PET imaging. 6
• Narrowed arterial lumen due to intimal hyperplasia. 6

Important Caveats

• Imaging should never delay initiation of high-dose glucocorticoid treatment when GCA is strongly suspected, particularly with visual symptoms or jaw claudication. 1, 3
• Imaging can remain positive for diagnosis even after glucocorticoids are started, unlike temporal artery biopsy which may show reduced inflammatory changes after 2 weeks of treatment. 3
• The choice of imaging modality should be guided by local expertise, equipment availability, and the clinical presentation (cranial vs. large vessel predominant symptoms). 1