Renal involvement of polyarteritis nodosa: CT and MR findings

To evaluate the imaging findings in patients with renal involvement of Polyarteritis nodosa (PN) to diagnose as early as possible.

Four patients diagnosed as having PN participated in the present study. Two patients underwent abdominal dynamic CT, one underwent only pre- and post-contrast CT, and the remaining patient underwent only noncontrast CT and MR imaging, including dynamic contrast study.

The common findings of CT and MR imaging were diffuse enlargement, multiple small wedge-shaped less-enhanced areas on dynamic contrast study, and indistinctness of the margin between the cortex and medulla on equilibrium-phase CT. Renal arteriogram showed multiple microaneurysms on arterial phase image in all four cases, and PN was diagnosed. The common CT and MR findings of renal involvement of PN mimicked those of pyelonephritis, when microaneurysms were not demonstrated.

The differentiation between PN and pyelonephritis on CT and MR imaging is difficult. Therefore, the radiologist should be familiar with the imaging findings of renal involvement of PN. When PN is suspected, angiography should be performed as early as possible to make a definite diagnosis.