Abdominal aortic aneurysm: Rupture associated with the high-attenuating crescent sign

PURPOSE: To determine the histopathologic features of the ruptured abdominal aortic aneurysm associated with the high-attenuating crescent sign on computed tomographic (CT) scans and to suggest a possible mechanism for the rupture. MATERIALS AND METHODS: Histopathologic examination was performed with specimens from six patients with a ruptured aneurysm associated with the high-attenuating crescent sign and from eight patients with a nonruptured aneurysm and in whom the high-attenuating crescent sign was not present. RESULTS: Acute hemorrhage in the mural thrombus or aneurysmal wall coincident with the high-attenuating crescent sign was present in all six patients with a ruptured aneurysm. Clefts with seeping blood in the mural thrombus were seen in four patients with a ruptured aneurysm; intact specimens of the mural thrombus were not obtained in two patients because the hemorrhagic thrombus was fragile. Clefts with seeping blood were scattered from the inner to the outer layers of the mural thrombus. In the eight patients with uncomplicated aneurysm, no hemorrhage in the mural thrombus or aneurysmal wall was noted, and no clefts were seen. CONCLUSION: The cause of high-attenuating crescents in a ruptured aneurysm may be attributed to hemorrhage in the mural thrombus or in the aneurysmal wall.