Vasculitis is an inflammation of the vessel walls. Vasculitis diagnosis can be difficult because the signs and symptoms are nonspecific and can mimic other conditions such as infection, malignancy, thrombotic disorders, and connective tissue diseases. The affected vessels are reflected in the clinical symptoms. Large vessel vasculitis is characterized by limb claudication, absent pulses, and unequal blood pressure, whereas small vessel vasculitis is characterized by palpable purpura and proteinuria. Because medium vessels are defined as main visceral arteries and their initial branches, symptoms vary depending on the vessels involved.

A detailed clinical history, physical examination, and focused laboratory investigation are essential for evaluating vasculitis. Non-invasive imaging is also useful for determining the extent of the disease. Computed tomography (CT) is commonly used as the initial imaging study for vasculitis because it can allow the evaluation of vascular wall change and the location and extent of the lesion with excellent spatial resolution. Ultrasonography may be used for the evaluation of superficial arteries, such as temporal, carotid, and axillary arteries. Using magnetic resonance imaging (MRI) it is possible to depict vessel wall edema and mural contrast enhancement as signs of vascular inflammation, whereas 18F-Fluorodeoxyglucose positron emission tomography (PET) shows the activity of vessel wall inflammation.