Isolated thoracic aortitis: clinicopathological and immunohistochemical study of 11 cases.

Isolated thoracic aortitis (ITA) is diagnosed in a variable proportion of patients operated on for dilation/aneurysm of ascending aorta. The etiopathogenesis of ITA remains unclear. We studied 11 cases of ITA in order to determine the role of IgG4-mediated immune responses in its pathogenesis. The series included nine women and two men aged 52-79 years. All patients developed aortic incompetence due to dilation/aneurysm of ascending aorta. None of the patients had a history of IgG4-related disease neither did they develop features of such disease during the follow-up period. The microscopic findings included the presence of lymphoplasmacellular fibrosing infiltrate of varied intensity involving the adventitia and media of aorta. This inflammation was associated with severe medial elastic fiber defects. Obliterative phlebitis of the vasa vasorum was absent. Immunohistochemically, the inflammatory infiltrate comprised T- and B-lymphocytes as well as plasma cells. The plasma cell population was polyclonal with a predominance of IgG-producing cells. In all the cases, IgG4-producing plasma cells were detected. In five cases, the count exceeded 20 cells per high-power field. The IgG4/IgG ratio ranged from 0.07 to 0.98 (median 0.55). In six cases with the ratio >0.50, severe adventitial fibrosis was present. To the best of our knowledge, ours is the first study focused on investigating the role of IgG4-positive plasma cells in the development of ITA. Our results suggest that a subset of ITA may represent aortic manifestation of IgG4-related disease. Further research is necessary in order to clarify this issue.