Temporal artery ultrasound is a non-invasive diagnostic imaging technique that uses high-frequency sound waves to create real-time images of blood vessels near the temples. This allows medical professionals to visualize their structure and blood flow, aiding in a comprehensive evaluation of arterial conditions.
Purpose of the Ultrasound
The primary purpose of a temporal artery ultrasound is to aid in the diagnosis of Giant Cell Arteritis (GCA), also known as temporal arteritis. GCA is a serious autoimmune condition characterized by inflammation in medium and large-sized blood vessels, particularly those in the head and neck, such as the temporal arteries. If left untreated, GCA can lead to severe complications, including irreversible vision loss in 15-25% of cases, and in some instances, stroke.
Symptoms that often prompt a temporal artery ultrasound include a new onset of headache, especially around the temples, scalp tenderness, or pain in the jaw or tongue when chewing. Patients may also experience vision changes, such as blurry vision, double vision, or even sudden, complete vision loss. Other general symptoms like fever, fatigue, and unexplained weight loss can also be present. GCA predominantly affects individuals over 50 years old and has a higher incidence in women and those with a history of polymyalgia rheumatica.
Diagnosing GCA can be challenging because its early symptoms often resemble other common conditions. Therefore, doctors often use a combination of physical examination, blood tests to check for inflammation markers like erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), and imaging tests. The ultrasound helps differentiate GCA from other conditions by directly visualizing the affected arteries.
The Ultrasound Procedure
Minimal preparation is typically required. Patients lie down, often with their head supported, to ensure comfort and access to the temporal region. Loose clothing or a gown may be recommended for easy access.
During the procedure, a trained sonographer applies a small amount of clear, water-soluble gel to the skin over the temporal arteries, located in front of the ears and extending up to the scalp. This gel helps the transducer, a small handheld device, glide smoothly and ensures good contact for sound wave transmission. The sonographer gently presses the transducer against the skin and moves it along the arteries.
The ultrasound typically takes about 30 minutes. Patients may feel slight pressure from the transducer, but there is no discomfort or recovery time.
Interpreting the Findings
Medical professionals look for specific signs during a temporal artery ultrasound to diagnose conditions like GCA. One of the most significant findings is the “halo sign,” which appears as a uniform, ill-defined, dark rim surrounding a segment of the artery. This sign indicates thickening of the vessel wall due to inflammation and fluid accumulation. A halo thickness from the inner to the middle layer of the artery wall of 0.4 mm can be sensitive for arteritis, while a thickness of 1.0 mm is highly suggestive.
Another important finding is the non-compressibility of the temporal artery. In a healthy artery, applying pressure with the ultrasound transducer will cause the vessel to fully compress and disappear from view. However, in cases of GCA, the inflamed and thickened arterial wall may remain visible even under compression, a phenomenon known as the “compression sign.” This sign has a sensitivity of 75-79% and a specificity of 100% for GCA diagnosis.
A radiologist or a specialist with expertise in vascular ultrasound interprets the images and provides a detailed report of the findings. A “normal” result would show temporal arteries with thin walls and unobstructed blood flow, without any signs of thickening or inflammation. An “abnormal” result, on the other hand, would indicate the presence of a halo sign, non-compressibility, or areas of narrowing (stenosis) or blockage (occlusion) within the arteries.
Advantages and Limitations
Temporal artery ultrasound offers several advantages over other diagnostic methods, particularly a temporal artery biopsy (TAB), traditionally the gold standard for GCA diagnosis. Ultrasound is non-invasive, avoiding surgical risks like wound infection, bleeding, or facial nerve injury associated with a biopsy. It also provides immediate results, allowing for quicker diagnosis and initiation of treatment, which is beneficial in preventing irreversible complications like vision loss.
The ultrasound can also evaluate the entire length of the temporal artery and its branches, potentially overcoming the challenge of “skip lesions” where inflammation may be patchy. This can lead to false negatives in a biopsy if the sampled segment is not affected.
Despite its benefits, temporal artery ultrasound has limitations. Its accuracy can be influenced by the skill and experience of the sonographer performing the scan, making it operator-dependent. There is also a potential for false negatives, as some inflamed segments might be missed, especially if the scan length is insufficient. Conversely, false positives can occur, as other conditions like atherosclerosis or other forms of vasculitis can sometimes mimic the halo sign.
A negative ultrasound result does not always definitively rule out GCA, especially if clinical suspicion remains high. In such cases, or if the ultrasound findings are inconclusive, a temporal artery biopsy may still be necessary to confirm the diagnosis. The sensitivity of ultrasound has been reported to range from 54% to 77%, with specificity from 79% to 96%, depending on the study and comparison method.