Inflammatory aneurysm of the abdominal aorta: anatomo-clinical study on 16 cases and pathogenetic hypothesis

BACKGROUND. Inflammatory aneurysms of the abdominal aorta constitute an anatomoclinical entity characterised by prominent thickening and fibrosis of the aneurysmal wall, extending to the adjoining structures. Etiology, pathogenesis and relation with atherosclerosis still remain controversial. METHODS. Sixteen consecutive patients undergoing surgery for inflammatory aneurysm of the abdominal aorta between March 1987 and December 1990 were studied (Group I); as a control, a series of 16 consecutive patients operated on in the same period for atherosclerotic aneurysm of the abdominal aorta was selected (Group II). As far as clinical history and symptoms are concerned, the comparison between the two groups revealed significant differences only for hydronephrosis (exclusively present in Group I, p < 0.05) and abdominal pain (more frequent in Group I, p < 0.01). The microscopic study of the aneurysmal wall was performed by scoring its histological features (atherosclerotic lesions, medial and adventitial fibrosis, inflammatory infiltrates and lymphatic stasis) from 1+ to 3+. RESULTS. As regards the microscopical features, atherosclerotic lesions were present in all the examined cases, whereas periadventitial fibrosis appeared in all the aneurysms of Group I and in none of Group II; the comparison between the two groups revealed further significant differences for extensive intimal calcification (exclusively present in Group II, p < 0.05), fibrous replacement of the tunica media (more thorough in Group I, p < 0.02), and the extent of inflammatory infiltrates (more prominent in Group I, p < 0.05). CONCLUSIONS. From the scarcity of pathognomonic features in both case-history and clinical presentation, the constant coexistence of prominent atherosclerotic lesions, and the progressive trend of the pathologic features, inflammatory aneurysms may be inferred to be a variant of atherosclerotic ones, characterised by a particular prominence of inflammation and fibrosis. The frequent occurrence of dilation of both periaortic lymphatic vessels and lymph node sinuses, even in "incipient" aneurysms, supports the hypothesis that it may be the lymphatic stasis which determines periaortic fibrosis. Finally, atherosclerotic components passing into periaortic fibrosis and eliciting granulomatous reaction were observed in two Group I cases featuring prominent "inflammatory" symptoms; such a finding favours the hypothesis that an immune reaction against some components of the atherosclerotic plaque may lead to the pronounced inflammatory response that is peculiar of inflammatory aneurysms.