DEMONSTRATION OF MICROANEURYSMS AT THE INTERLOBULAR ARTERIES OF THE KIDNEYS IN MICROSCOPIC POLYANGIITIS - A 3-DIMENSIONAL STUDY

Aneurysms, mostly saccular, of the medium-sized muscular arteries are frequently encountered in classic polyarteritis nodosa, whereas their occurrence in smaller arteries is unclear. The objective of this study is to clarify the three-dimensional morphology of the small-sized mus cular arteries involved in microscopic polyangiitis (MPA). Six autopsy cases of MPA of the acute inflammatory stage were chosen. Using seria l paraffin-embedded sections of the kidney, vasculitic lesions observe d in the interlobular arteries were three-dimensionally reconstructed All of the 19 lesions showed microaneurysms, of which 18 were sausage- shaped and the other was saccular. In the former type, average outer d iameter at the most expanded point was 235.4 +/- 83.8 mu m (mean +/- S D), which was 2.78 +/- 0.73 times that of an uninvolved adjacent arter ial diameter. The major axis-minor axis ratio in a cross-aneurysmal se ction was 1.17 +/- 0.16, indicating rather regular centrifugal expansi on of the aneurysm. The aneurysmal length was 742.7 +/- 254.8 mu m The se sausage-type aneurysms showed whole circumferential vasculitic invo lvement, whereas the saccular-type aneurysm contained an uninvolved ar terial portion. In both types, the luminal spaces showed similar three -dimensional features to the outer surface of microaneurysms. It was c oncluded that the interlobular arteries of the kidneys in MPA were cha racterized by formation of microaneurysms, most of which were sausage- shaped. Copyright (C) 1998 by W.B. Saunders Company.