Imaging in Polyarteritis Nodosa 

Polyarteritis nodosa (PAN) is an autoimmune systemic inflammatory vasculitis that results in transmural fibrinoid necrosis with surrounding inflammation in small and medium-size vessels (see the following images). This condition commonly affects the kidneys, heart, liver, and gastrointestinal (GI) tract, with the kidney being the organ most commonly involved (79% of cases at autopsy).^{[1, 2]}

Preferred examination

For an accurate diagnosis of polyarteritis nodosa, selective arteriography is the criterion standard. In the past, biopsy was used.

Analysis of biopsy specimens from the subcutaneous nodules or skeletal muscle may be helpful in establishing the diagnosis, although biopsy has a success rate of only 20-35%.

Limitations of techniques

Although biopsy was used more extensively in the past, this procedure has fallen into disfavor because of sampling errors and its low success rate. Angiography can be helpful in confirming or supporting the clinical diagnosis of polyarteritis nodosa; however, this procedure is an invasive test.^{[3, 4, 5]}

Differential diagnosis and other problems to be considered

The differential diagnosis includes Churg-Strauss disease, Churg-Strauss syndrome, leukocytoclastic vasculitis, systemic lupus erythematosus, and Wegener granulomatosis. Other conditions that should be considered are acute glomerulonephritis, drug-induced vasculitis, and vasculitis associated with lupus, scleroderma, rheumatoid arthritis, and Wegener granulomatosis.

Radiologic intervention

Transcatheter embolization should be considered only in cases involving larger aneurysms, because of the potential for rupture, and when bleeding occurs from rupture of the aneurysm.

Excretory urographic findings are often normal in patients with polyarteritis nodosa. Subtle findings can include increased renal size, ureteral dilatation, perinephric hematoma, and renal infarction.^[6]

CT scan findings are nonspecific, but they include bowel wall thickening; vascular engorgement; haziness in the mesentery; ascites; ureteral dilatation; renal, hepatic, and splenic infarctions; and perinephric hematoma.^[7]

Selective arteriography is the best modality for evaluating and diagnosing polyarteritis nodosa. The most striking pathognomonic finding is the appearance of aneurysms, usually microaneurysms, which are believed to be caused by rupture of a vessel wall (see the images below).

Microaneurysms are often multiple, usually numbering 10 or more in any single visceral circulation. In most patients, they are 2-5 mm in size. Saccular aneurysms (1-5 mm) of small and medium-sized vessels are typically found. Usually, microaneurysms can be identified in 60-80% of patients, and although they are considered to be pathognomonic for polyarteritis nodosa, these lesions can be encountered in other vasculitides. The aneurysms are caused by segmental occlusion of the arteries with weakening of the arterial wall, which occurs as a result of the necrotizing inflammatory process.

The most common sites of involvement of polyarteritis nodosa are the branching points and bifurcations of arteries. Common sequelae of this condition are intravascular thrombosis, aneurysm rupture, and arterial occlusion with resultant infarctions. In the kidneys, these sequelae can cause ischemic atrophy and hemorrhage. The hemorrhage is usually intrarenal, perinephric, subcapsular, or retroperitoneal.

Other angiographic features of polyarteritis nodosa include tortuous vessels with irregular lumina, segmental luminal narrowing or dilatation, infarctions, vascular irregularity, segmental occlusions, and hypervascularity in regions of PAN.^{[3, 4, 5]}

Degree of confidence

Although angiographic findings of microaneurysm, ectasia, and/or occlusive disease suggest the diagnosis of polyarteritis nodosa, these findings may be seen in other vasculitides, including rheumatoid vasculitis, Churg-Strauss syndrome, necrotizing angiitis associated with drug abuse, and systemic lupus erythematosus. Correlation with the clinical evaluation is important.