Increased metabolic activity highlighted by positron emission tomography/computed tomography in the wall of the dissected ascending aorta in a patient with Horton disease.

H orton disease or giant-cell arteritis (GCA) is a chronic systemic vasculitis involving typically medium and large arteries. Giant-cell arteritis is a panarteritis characterized by a granulomatous inflammation, with lymphocytes, macro-phages, and multinucleated giant cells related to autoimmune T-cell reactivity. 1 Compared with conventional imaging tools (ultrasound, computed tomography (CT), MRI, and contrast angiography) that provide anatomic and morphological information , recent available imaging techniques such as positron emission tomography (PET)/CT provide metabolic assessment of the arterial wall. During the early 2000s, Sakalihasan et al 2 observed a close correlation between clinically unstable abdominal aortic aneurysms and increased uptake of 18 F-fluoro-2-deoxy-d-glucose (FDG) in the aneurysmal wall. A few years later, Hautzel et al 3 studied the assessment of giant-cell arteritis with PET/CT. We describe a case of Horton disease involving the thoracic aorta and complicated with acute aortic dissection in a woman with a previous diagnosis of thoracic aortic aneurysm. In July 2011, a 66-year-old woman was referred to a cardiol-ogy center for evaluation of a recent mild hypertension related to use of high doses of corticosteroids. In December 2010, she had developed severe headache, rapid loss of weight, and elevation of sedimentation rate as high as 120 mm. Hor-ton disease was diagnosed in April 2011 on temporal artery biopsy. During the first cardiologic examination, all features were normal, including revision of recent chest radiography, aortic root dimension (38 mm), and aortic valve function (except a minimal aortic regurgitation). Because of increased D-dimer level (4261 ng/mL) and the presence of limited deep venous thrombosis, a pulmonary V/Q single-photon emission CT/CT was performed to exclude pulmonary embolism. The low-dose CT part of this examination revealed a dilated arch and descending thoracic aorta. Contrast-enhanced CT confirmed the diagnosis of thoracic aortic aneurysm, with an estimated diameter of 60 mm for the aortic isthmus and for the descending aorta. (Figure 1A). The regular preoperative workup included routinely an FDG-PET/CT examination in all patients referred for aortic aneurysm, diagnosed initially by CT scan, and scheduled for surgery. This prospective trans-lational study was designed and conducted within the framework of the European program Fighting Aneurysmal Disease. In this case, 18 F-FDG PET/CT, which was performed 2 weeks later, showed an unexpected 12-mm increase in the size of the aneurysm (maximal diameter, 72 mm) and an asymptomatic dissection with an entry hole in the proximal ascending (A1) aortic segment. The FDG uptake was particularly high …