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.

Segmental arterial mediolysis with accompanying venous angiopathy: a clinical pathologic review, report of 3 new cases, and comments on the role of endothelin-1 in its pathogenesis.

The authors review 20 cases of segmental arterial mediolysis (SAM) including 3 newly reported cases. SAM developed in areas of vascular distention in 2 of the latter cases: 1 in utero in the heart of a recipient of a twin transfusion syndrome and the other in the jejunum secondary to partial venous obstruction. In the third case, it occurred in a patient with Raynaud disease. Characterizing SAM are injurious and reparative lesions that occur in the media and/or at the adventitial medial junction. Four distinctive alterations are recognized: (1) mediolysis, (2) a tearing separation of the outer media from adventitia, (3) arterial gaps, and (4) a florid reparative response that replaces zones of mediolysis and fills areas of medial adventitial separation. The repair can transform SAM into lesions indistinguishable from common types of fibromuscular dysplasia (FMD.) A venous angiopathy involving large and medium-sized veins accompanies SAM. It features medial muscle vacuolar change with lysis leading to apparent separation of residual muscle bundles. Immunostaining shows endothelin-1 (ET-1) decorating adventitial capillaries in SAM and neighboring arteries, in capillaries of adjoining tissues, and outlining smooth muscle cell membranes in adjacent veins including those of the venous angiopathy. The significance of these changes is uncertain. Vasospasm is believed to cause SAM, but ET-1 is not the direct pressor agent responsible for this condition. The reason(s) for synthesis and release of ET-1 in SAM are still hypothetical, but local perturbations in vascular tone may be an important factor. ET-1 may be indirectly play a role in SAM by cross-talking and potentiating the activities of other vasoconstrictors such as norepinephrine and by orchestrating its reparative phase.