Polyarteritis Nodosa

Polyarteritis is frequently seen in aging rats. The preva­lence is higher in males. Arterial lesions most frequently occur in medium-size arteries of the mesentery, pan­creas, kidney, pancreaticoduodenal artery, testis, and most other organs, except the lung.

FIG. 2.58. Mesentery and intestines of an aged rat with polyarteritis. Note the nodular dilation and tortuosity of the mesenteric vessels. (Source: D. Imai, University of California, Davis, CA. Reproduced with permission from D. Imai.)

(Fig. 2.58). On microscopic examination, there is intimal fibrinoid degeneration and thickening of the media of affected arteries, with smudging of the normal architec­ture. Infiltrating leukocytes consist of mononuclear cells, with a few neutrophils (Fig. 2.59). There are marked variations in the size and contours in the lumen of affected vessels, and thromboses, occasionally with recanalization, may occur.