The role of 18F-fluorodeoxyglucose positron emission tomography for vascular imaging

Vasculitides are caused by a pathological inflammatory reaction inside the arterial wall that may involve all three layers (endothelium, media and adventitia). They are typically grouped according to the caliber of the vessels involved-large, medium or small. The diagnosis of vasculitis should be made rapidly because of the risk of ischemic complications due to vascular occlusion and immunosuppressive treatment initiated without delay. Histological analysis of vascular samples remains the gold standard for the diagnosis but may be inconclusive or not accessible. Non-invasive imaging is playing an increasing role for the diagnosis of vasculitis. Among the different imaging modalities available, ¹⁸F-fluorodeoxyglucose positron-emission tomography (FDG-PET) has demonstrated its interest for the diagnosis of vasculitis. FDG is an analogue of glucose bound to a positron emitter, that accumulates in activated inflammatory cells. FDG-PET imaging provides high sensitivity for the detection of vascular wall inflammation associated with vasculitis. PET imaging has a spatial resolution of only 4-5 mm which is adequate for large vessel vasculitis such as giant cell or Takayasu arteritis, but insufficient for medium or small vessels. FDG-PET has demonstrated high diagnostic performance for the diagnosis of giant cell arteritis and Takayasu arteritis as well as for monitoring the regression of vascular inflammation under immunosuppressive therapy. The role of FDG-PET for the detection and prediction of relapse remains, however, largely discussed. In addition to its role in inflammatory vasculitis, FDG-PET can also help identify vascular complications of sepsis due to septic emboli, such as infectious aortitis or mycotic aneurysms.