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Ultrasound is a valuable tool in the diagnostic workup of small- and medium-vessel vasculitis.
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In large-vessel vasculitis (giant cell arteritis and Takayasu’s arteritis), ultrasound delineates characteristic homogeneous artery wall swelling.
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Stenoses and acute occlusions of temporal arteries are highly suspicious of vasculitis.
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Ultrasound of the axillary arteries provides important information of the presence or absence of large-vessel giant cell arteritis.
Vasculitides are autoimmune diseases that are characterized by an inflammation of the vessel wall. The Chapel Hill nomenclature describes primary vasculitides as small-vessel vasculitides, medium-vessel vasculitides, and large-vessel vasculitides. Secondary vasculitides are usually small-vessel vasculitides that occur in connection with infections, drug intolerance, and other autoimmune diseases, such as rheumatoid arthritis and lupus erythematosus.
Ultrasound is a valuable tool for the diagnostic workup in small-vessel vasculitis. It aids in establishing the diagnosis of medium-vessel vasculitis and in large-vessel vasculitis, and it is useful for monitoring large-vessel vasculitis.
Vasculitides by Vessel Size
Small-Vessel Vasculitis
Diagnostic workup in small-vessel vasculitis includes examination of abdominal organs, including kidneys, pleura, and heart. Ultrasound of the kidneys aids in differentiating the causes of renal insufficiency. Severe glomerulonephritis leads to a hyperechoic appearance of the renal cortex ( Fig. 22-1 ).
Ultrasound of the spleen may detect splenomegaly or infarctions that are characterized by clearly delineated hypoechoic areas in the spleen ( Fig. 22-2 ). Even small-vessel vasculitides may lead to narrowing of abdominal vessels. Figure 22-3 shows stenosis of the celiac trunk in a patient with Churg-Strauss syndrome, who also had stenosis of the superficial mesenteric artery. The patient developed angina abdominalis, which was reversible with corticosteroid and azathioprine treatment. Ultrasound can detect renal artery stenosis and differentiate extrarenal from intrarenal causes of arterial hypertension. Figure 22-4 shows normal renal arteries in a patient with Takayasu’s arteritis.
Echocardiography may identify abnormalities that are directly related to the disease in 31% of patients with Wegener’s granulomatosis. These findings include wall motion abnormalities ( Fig. 22-5 ), left ventricular systolic dysfunction ( Fig. 22-6 ), and pericardial effusion ( Fig. 22-7 ).
Ultrasound is a sensitive tool for detecting even small pleural effusions ( Fig. 22-8 ). It delineates so-called lung comets in pulmonary fibrosis. They are hyperechoic comet tails fanning out from the lung surface and originating from subpleural interlobular septa thickened by fibrosis. However, lung comets also occur in pulmonary edema.
Chest computed tomography (CT) remains the gold standard for evaluating fibrotic abnormalities that particularly occur in microscopic polyangiitis and in Churg-Strauss syndrome and for delineating nodular lesions that are typical for Wegener’s granulomatosis. CT and magnetic resonance imaging (MRI) remain the first-line modalities for evaluating sinonasal vasculitis. For cerebral vasculitis, MRI remains the imaging method of choice.
Medium-Vessel Vasculitis
Polyarteritis nodosa leads to aneurysms of abdominal arteries. Angiography and MR angiography (MRA) typically are used to detect these aneurysms. Cases in which aneurysms are detected by ultrasonography in polyarteritis nodosa have not been described. One case with testicular necrosis demonstrated arterial wall swelling in the testicular arteries was described in a patient with large-vessel vasculitis.
Kawasaki’s disease is an acute, self-limiting vasculitis of childhood. It is characterized by fever, polymorphous exanthema, membranous desquamation of fingertips, conjunctivitis, mucositis, and unilateral cervical lymphadenopathy. Aneurysms occur in coronary arteries in about 25% of untreated cases and in other arteries. Vasculitis of the coronary arteries may lead to coronary artery occlusion and impaired left ventricular function. Coronary aneurysms can be detected by transthoracic echocardiography in most nearly all of the patients, most of whom are between 2 and 6 years old. The overall sensitivity and specificity of cross-sectional echocardiography for correctly identifying coronary aneurysms are 95% and 99%, respectively, compared with angiography. Intracoronary ultrasound reveals increased thickness of the arterial intima-media complex.
Echocardiography is recommended, followed by stress testing, if coronary stenosis is suspected. Stress testing can be combined with echocardiography or with scintigraphy. Angiography still has a place in interventional therapy and for situations in which the results of noninvasive techniques remain ambivalent. MRA and CT angiography (CTA) are newer alternatives for noninvasive imaging. Intracoronary ultrasound remains a research tool because of its invasiveness.
Large-Vessel Vasculitides
Giant cell arteritis (GCA), also called temporal arteritis, and Takayasu’s arteritis are the two large-vessel vasculitides listed in the Chapel Hill nomenclature. Newer entities have been described because of the use of ultrasound, MRI, MRA, CT, and positron emission tomography (PET). They include large-vessel GCA with vasculitis of the proximal arm arteries and idiopathic aortitis. Patients with polymyalgia rheumatica (PMR) may have temporal arteritis or large-vessel GCA, even if they do not exhibit symptoms or clinical signs of vasculitis (i.e., pure PMR). Moreover, some patients with Behçet’s disease exhibit large-vessel vasculitis. Large vessels, particularly the common superficial femoral and popliteal arteries, are most commonly involved in vasculitic Behçet’s disease, and they have the clinical and sonographic appearance of deep venous thrombosis ( Fig. 22-9 ).
Vascular Ultrasound for the Rheumatologist
Rheumatologists should be aware of several definitions used in vascular ultrasound. In Doppler mode , the Doppler effect is assessed. The Doppler principle states that sound waves increase in frequency when they reflect from objects (e.g., red blood cells) moving toward the transducer and decrease when they reflect from objects moving away. This information is converted into sound. It is possible to delineate flow curves and to determine the direction of blood flow.
Continuous-wave Doppler assesses flow without providing anatomic images. This method detects all the information of an axis through the body. The information is converted into sound or into curves that are displayed on a screen. Continuous-wave Doppler does not provide information about distances.
Pulsed-wave Doppler is an advanced mode compared with continuous-wave Doppler. It detects the information in a selected anatomic region of the Doppler beam axis. The anatomic region is selected on the gray-scale image or on the color Doppler image.
Color Doppler mode combines the Doppler effect with real-time imaging. The real-time image is created by rapid movement of the ultrasound beam. The information from Doppler ultrasound is integrated in the gray-scale image as a color signal. This signal indicates the direction of blood flow. Red signals indicate flow that is directed toward the ultrasound probe. Blue signals indicate flow that is directed away from the probe.
Duplex mode is the combination of real-time imaging and Doppler ultrasound. It depicts the anatomic image with color signals and the Doppler curves. This technique allows an estimate of the velocity of flow from the Doppler shift frequency in combination with an angle correction program. Although the temporal arteries are small, the flow velocities are comparable to those of larger arteries. The average maximum systolic velocities of temporal arteries are 50 to 60 cm/s. It is not necessary to use power Doppler ultrasound, which does not provide any information about the aliasing phenomenon (mixture of colors) in stenoses.
Types of Vasculitis
Giant Cell Arteritis
GCA and PMR occur more often than previously thought. The prevalence of PMR and GCA in the United States is about 0.1% and 0.3%, respectively. GCA occurs in at least 15% of PMR patients, and about 40% of GCA patients exhibit symptoms of PMR. In 7 of 102 patients with pure PMR, temporal artery ultrasound detected temporal arteritis, PET studies showed large-vessel GCA in up to 31% of PMR patients. GCA is the most common primary vasculitis in a white population. The clinical appearance varies considerably among patients.
GCA occurs almost exclusively in people older than 50 years. Localized headache in the temporal region occurs in 74% of patients. Sixty-four percent of patients have tender, often swollen, temporal arteries. Pulsation may be reduced, jaw claudication occurs in 37% of patients, and 32% have eye involvement, which is most commonly caused by anterior ischemic optic neuropathy. This may cause blindness of the involved eye. The erythrocyte sedimentation rate (ESR) is greater than 50 mm/hr in 85% of patients. Most patients have an ESR greater than 20 mm/hr. Temporal artery histology is positive in 85% of patients with temporal arteritis.
Ultrasound findings for the temporal arteries were first described in 1995. The lumen of healthy common superficial temporal arteries has an average diameter of 1.7 mm. The frontal and parietal branches have diameters of 0.7 to 0.8 mm ( Fig. 22-10 ). The vessel wall of the branches, including the two layers of temporal fascia, have diameters of 0.7 mm. Ultrasound machines can provide axial and lateral resolutions of 0.1 mm. It is therefore easy to obtain information about the vessel lumen and wall, pulsatility, and blood flow characteristics. The sonographer can communicate with the patient during the examination, correlate symptoms with ultrasound findings, and explain the findings.
When applied to the temporal arteries, duplex ultrasound shows the following :
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Edema is seen as a dark, hypoechoic, circumferential wall thickening (i.e., halo) that occurs around the artery lumen ( Fig. 22-11 ). It disappears with corticosteroid treatment after 2 to 3 weeks.
F igure 22-11
Acute temporal arteritis with hypoechoic wall swelling (arrows) of the parietal branch is shown in longitudinal ( A ) and transverse (halo sign) ( B ) views.
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Stenosis causes increased blood flow velocities and turbulence. Color Doppler ultrasound shows a mixture of colors and persisting color signals in diastole. Doppler curves delineate blood flow velocities of more than twice the rate than recorded in the area before the stenosis, perhaps with waveforms demonstrating turbulence ( Fig. 22-12 ).
F igure 22-12
Duplex ultrasound of the frontal branch in a patient with acute temporal arteritis shows hypoechoic wall swelling. The power-wave Doppler curves show increased systolic and diastolic flow velocities. The maximum systolic flow velocity is 180 cm/s.
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Occlusion of the temporal artery is seen in the gray-scale image, but color signals are absent ( Fig. 22-13 ).
F igure 22-13
Transverse view of acute temporal arteritis with hypoechoic occlusion of the frontal ramus shows hypoechoic material within the former artery lumen and no color signals.
Inflamed temporal arteries are less pulsatile.
The sonographer needs moderate- or high-quality color Doppler ultrasound equipment with a more than 8-MHz linear probe, experience with vascular ultrasound, and standardized ultrasound machine settings. The color signal should exactly cover the artery lumen. If it extends over parts of the vessel wall, inflammation may be missed. If it covers only the center of the lumen, vasculitis may be falsely diagnosed. The color sample steering should be maximal. The pulse repetition frequency (PRF) should be set at about 2 to 2.5 KHz. A sonographer should have examined at least 30 to 50 persons without GCA to be sure about the normal appearance of temporal arteries.
The sonographer starts performing color Doppler ultrasound with a longitudinal scan in front of the left ear so that the patient can follow the examination at the ultrasound monitor ( Fig. 22-14 ). The sonographer follows the parietal branch longitudinally and moves the probe back transversely to find the frontal branch, which is followed longitudinally and transversely. The superficial temporal arteries with the parietal and longitudinal branch should be examined in two planes on both sides in full length. I perform pulsed-wave Doppler ultrasound (i.e., duplex ultrasound) only in areas with suspected stenosis (i.e., if systolic aliasing and diastolic persistence of flow occur). If it is not possible to detect color signals in a temporal artery that may be detected with gray-scale ultrasound, it is necessary to reduce the PRF and increase the color gain to be sure not to miss slow blood flow.
