A 56-year-old male presents with the sudden onset of excruciating pain. He describes the pain as beginning in the anterior chest, radiating to the back, and then moving downward into the abdomen. His blood pressure is found to be 160/115. Your differential diagnosis includes myocardial infarction; however, no changes are seen on ECG, and you consider this to be less of a possibility. You obtain an x-ray of this patient’s abdomen and discover a “double-barrel” aoa. This abnormality most likely results from
Correct Answer: Loss of elastic tissue in the media
Description: Dissecting aneurysms are usually the result of cystic medial necrosis of the aoa. This abnormality results from loss of elastic tissue in the media and is associated with hypeension and Marfan's syndrome. Most cases of dissecting aneurysms involve a transverse tear in the intima and are located in the ascending aoa, just above the aoic ring. The pain caused by a dissecting aneurysm is similar to the pain caused by a myocardial infarction, but it extends into the abdomen as the dissection progresses. Additionally, the blood pressure is not decreased with a dissecting aneurysm unless the aoa itself has ruptured. In contrast, berry aneurysms, found at the bifurcation of aeries in the circle of Willis, are due to congenital defects in the vascular wall. Rupture of these aneurysms may produce a fatal subarachnoid hemorrhage. Berry aneurysms have been noted in about one-sixth of patients with adult polycystic renal disease and account for death in about 10% of patients with this type of polycystic renal disease. Syphilitic (luetic) aneurysms occur in the thoracic aoa and may lead to luetic hea disease by producing insufficiency of the aoic valve. Mycotic (infectious) aneurysms result from microbial infection during septicemia, usually secondary to bacterial endocarditis. They are prone to rupture and hemorrhage. The Ehlers-Danlos syndromes (EDSs) are a group of eight syndromes characterized by defects in collagen synthesis. In EDS IV there is deficient synthesis of type III collagen and a tendency to rupture of muscular aeries, including dissecting aneurysms of the aoa.
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