Figures 1 and 2: The aorta demonstrates a smooth intimal surface without aneurysm or dissection. The brachiocephalic artery, right carotid, and right vertebral artery are patent. Just distal to the right vertebral artery, there is a long segment of severe subclavian and axillary artery stenosis with reconstitution of the distal axillary artery. Small surrounding collateral vessels are present. The left common carotid and the origin of the left subclavian artery are patent. Immediately distal to its origin, the left subclavian artery emonstrates severe attenuation, giving off the left vertebral artery, which is patent. Distal to this, the left subclavian and axillary artery shows a long segment of severe stenosis with reconstitution of the distal axillary/brachial artery. Surrounding collateral vessels are again noted.

Takayasu’s arteritis.

Takayasu’s arteritis (TA; Pulseless syndrome) is an inflammatory and stenosing vasculitis of large and intermediate sized arteries. Takayasu’s arteritis most often affects females between the ages of 10 to 30 years. Although TA is more commonly seen in the Orient, the disease has a worldwide distribution. The etiology is of TA is unknown; however, it has been associated with an immune response gene in the D locus. Histologically, the nonspecific findings of this arteritis include extensive tissue destruction, connective tissue proliferation, and mononuclear cell infiltration in the adventitia and media of the arterial wall that can progress to cause secondary luminal changes including stenosis, occlusion, and dilatation. Clinical manifestations have been divided into early systemic (pre-pulseless) stage and a late occlusive (pulseless) stage. The systemic phase, seen in 50-66% of patients, consists of constitutional symptoms (fever, anorexia, weight loss, night sweats), arthralgias, myalgias, skin rash, pleuritis, cough, and sometimes transient evidence of local circulatory deficits (dizziness, syncope, claudication, angina, and hypertension). Local pain over the artery has been noted in up to one third of patients. Patients can also demonstrate an elevated erythrocyte sedimentation rate. The systemic phase lasts for several weeks and then resolves. The late occlusive (pulseless) phase, which is characterized by a chronic occlusive arteritis, can follow immediately after the systemic phase or after a latent period that can last for several decades. The occlusive arteritis characteristically involves the aorta (thoracic and abdominal), the branches of the aortic arch, and the pulmonary arteries. Upper extremity involvement is characterized by diminished or absent pulses, claudication, differences in systolic blood pressure between arms, and rarely Raynaud’s phenomenon. Additional symptoms, depending on the vessels involved, include dizziness, syncope, and visual disturbances. Gangrene is very rare because the gradual onset of occlusion permits the formation of collateral circulation. Vessel wall inflammation leading to arterial stenosis or occlusion may cause end organ ischemia (e.g. cerebrovascular accidents). Less often, aneurysms may produce sequelae such as aortic regurgitation and vascular dissection or rupture.

Diagnosis of Takayasu’s arteritis in the acute (pre-pulseless) stage is difficult but extremely important for prevention of progression to the pulseless stage. Conventional and digital subtraction angiography have been used for the evaluation of arterial steno-occlusive changes or aneurysm in Takayasu’s arteritis and are often necessary for the definitive diagnosis. However, angiography can sometimes be difficult to perform since certain patients may manifest stenosis in the aorta and its branch vessels that prevents catheterization and catheter replacement. In addition, angiography is often risky in patients suspected of having TA, since the frequency of ischemic complications resulting from this procedure is rather high, probably related to increased coagulative activity in patients with TA. Finally, during the early phase of TA, only mild luminal changes of the arteries may be present, without significant stenosis. These early changes may not be detectable by angiography.

Magnetic resonance angiography (MRA) is non-invasive imaging modality that can detect all the lesions within the aorta and its branch vessels. In addition, MRA can also demonstrate lesions in the pulmonary arteries, a finding specific to Takayasu’s arteritis. The extent of inflammation of the involved arterial segments and the degree and extent of stenosis, dilatation, aneurysms, and other abnormalities such as aortic wall thickening and mural thrombi can be assessed on T1-weighted spin-echo MR imaging in the axial and oblique sagittal places. On T2-weighted images, early arterial wall changes appear as a bright signal of edema in and around inflamed vessels. Contrast-enhanced MRA can reveal not only morphologic changes seen in TA, but can also demonstrate the subtle pathologic changes in the arterial wall. During the acute phase of TA, early inflammation of the wall of the aorta, its branches, and periadeventitial soft tissue can be observed as a high signal intensity post contrast T1-weighted images. In chronic TA cases, increased accumulation and delayed wash-out of contrast medium in the thickened aortic wall may suggest persistent activity of TA. In the quiescent state, contrast enhancement may not occur in the wall of the aorta or its branches, which may indicate extensive fibrosis.

MR imaging can be used to follow patients with TA for the development of complications and in the evaluation of response of TA to medical treatment by depicting decreased wall thickness of the involved arteries and the aorta. Studies have shown that MR imaging can clearly demonstrate the patency of palliative shunts or of angioplasty sites in patients with TA. Performance of conventional angiography, however, is still necessary in preoperative planning of bypass surgery and of percutaneous transluminal angioplasty.

References:

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