Segmental arterial mediolysis: unrecognized cases culled from cases of ruptured aneurysm of abdominal visceral arteries reported in the Japanese literature.

Segmental arterial mediolysis (SAM) is a rare nonatherosclerotic and noninflammatory arteriopathy that was proposed by Slavin et al. [Segmental mediolytic arteritis. A clinical pathologic study, Lab. Invest. 35 (1976) 23-29]. It mainly involves abdominal visceral arteries and is characterized by lytic degeneration of the media, resulting in intraabdominal bleeding. We collected 27 unrecognized cases of SAM by reviewing microscopic slides of cases of ruptured aneurysms of visceral arteries, except splenic and hepatic aneurysms, reported in the Japanese literature. This paper describes the pathological and clinical features of these cases. The symptom at onset was abdominal pain associated with intraabdominal bleeding in all cases. The most involved artery was the middle colic artery, accounting for 14 (50%), followed by gastric and gastroepiploic arteries, (6 and 5, respectively). Seventy-eight percent of aneurysms were of dissecting type and the rest of pseudoaneurysm type, except for one. Multiple aneurysms were found in 9 cases (33.3%). Pathological lesions were acute in all. The outcome of those who had surgery was good, even in those who had surgery for 1 ruptured aneurysm, leaving the others unmanaged. The relationship of SAM to fibromuscular dysplasia is discussed. Secondary changes in the wall of the accompanying vein to the affected artery are briefly described. It is emphasized that the majority of aneurysms of abdominal visceral arteries are gathered together as SAM as a definite clinical and pathological entity.