[Progressive enlargement and thrombosis of an anterior communicating artery aneurysm. Clinical, radiological and histological study (author's transl)].

A non operated aneurysm of the anterior communicating artery enlarged considerably over a seven years period; it finally thrombosed and behaved like a suprasellar tumor. The clinical course, the angiographic evolution and the anatomical examination allowed, in this case, to account for the increase in volume by progressive stretching of the wall, and not by incorporation of a false aneurysmal sack resulting from an encapsulated haematoma. Histologically, the wall of this giant aneurysm showed various changes : on the inner aspect, progressive thickening occurs, due to fibrous organization of mural thrombosis; in the depth, far from the nutrient sources, necrotic atheromatous like foci occur, which isolate an inner leaflet, prone to become nectrotic at a later stage. Distension of such a weakened wall may lead to several consequences; a progressive increase in volume of the aneurysm, partial ruptures with haemodissection starting from the aneurysmal lumen, or even complete rupture of the wall and subarachnoid haemorrhage. On the other hand, circulatory stasis, due to the important increase in volume, may facilitate progressive thrombosis of the aneurysm. The living character of the wall is emphasized by the coexistance of these unfavourable (degeneration, ruptures) and favourable (thrombosis, fibrous organization) features, which continuously influence the spontaneous evolution of the aneurysm.