This five-part review focuses on selected nonneoplastic diseases of the aorta and pulmonary trunk. Because many more diseases affect the aorta compared with the pulmonary vunk and right and left main pulmonary arteries, most of this review will be devoted to disorders of the aorta. Part I1 of this five-part series discusses complications of aortic dissection and aortic aneurysm. Key words: aorta dissection, aneurysm Complications of Aortic DissectionVarious complications and causes of death from acute aortic dissection are listed in Tables I and I I . ' -' Death is the most frequent complication, occurring in about 90% of untreated patients. The most frequent mechanism of death is complete rupture of the aorta (Fig. The rupture site commonly is near the site of the entrance tear; thus, the most frequent site of complete rupture is the ascending aorta. Although rupture of the outer wall of the false channel frequently leads to hemopericardium (Fig. l), blood also dissects into the adventitia of the wall of the false channel. The ascending aorta and pulmonary trunk have a common adventitia; thus. dissection of blood into the aortic adventitia permits access the to adventitia surrounding the pulmonary trunk (Figs. 2,3). As a result, ma-
This five-part review focuses on selected nonneoplastic diseases of the aorta and pulmonary trunk. Because many more diseases affect the aorta compared with the pulmonary trunk and right and left main pulmonary arteries, most of this review will be devoted to disorders of the aorta. Part IV of the series discusses cystic medial degeneration, trauma, and congenital diseases of the aorta.patients with Marfan's syndrome. Lesser degrees of this condition are probably acquired and may occur in response to hemodynamic stresses as present in systemic hypertension,' aortic valve stenosis? and bicuspid aortic valve.' Schlatman and Becke9 recently showed that certain amounts of elastic degeneration occur with normal advancing age. The extensive cystic medial degeneration with interrupted medial layers account for the diffuse dilation of the aorta as well as intimal tears that occur in patients with Marfan's disease. These terms describe a process of medial elastic fiber degeneration and deposition of acellular basophilic material. In mild forms of this condition, the elastic elements of the media are not noticeably affectedS4 With more basophilic deposition, medial fibers are interrupted and retract from sites of interruption. The areas of medial intermption produce acellular "cyst-like" spaces. In advanced forms of the disease, extensive areas of the elastic layers are interrupted (Fig. 1). These patients probably have a congenital abnormal media and have a change similar to that observed in External blunt trauma to the thorax may cause laceration of the Two anatomic sites are particularly wsceptible: the junction of the arch and the descending aorta. and the proximal part of the tubular segment of the axending aorta.5 The latter site is more common and has the potential for hemothorax or aneurysm formation. Traumatic rupture of the ascending aorta may cause either hemopericardium or prolapse of aortic valve cusps with secondary pure aortic reg~rgitation.~ Congenital D i s e a s e s of AortaCertain nonneoplastic disease of the aorta are congenital in origin: supravalvular aortic stenosis, coarctation of the aorta, aortic arch interruption, and sinus of Valsalva aneurysm. Supravalvular Aortic StenosisSupravalvular aortic stenosis is characterized by an obstructive anomaly in the tubular portion of the ascending aorta. Three anatomic variants are recognized: hourglass type, hypoplastic type, and membranous type.13 Occasionally, surgical specimens are submitted from patients with supravalvular aortic stenosis, including excised aortic membranes and/or excision of the narrowed segment. This condition may be associated with stenosis of branches of the aortic arch and pulmonary a r t e r i e~.~~.~~
Th~s five-part review focuses on selected nonneoplastic diseases of the aorta and pulmonary trunk. Because many more diseases affect the aorta compared with the pulmonary trunk and the right and left main pulmonary arteries, most of this review will be devoted to disorders of the aorta. Part V of this five-part series on diseases of the aorta and the pulmonary trunk focuses on nonneoplastic diseases of the pulmonary trunk and the right and left main pulmonary arteries.Key words: pulmonary arteries, pulmonary trunk, pulmonary aneurysm, pulmonary artery dissection Pulmonary Trunk and Right and Left Main Pulmonary ArteriesIn contrast to multiple congenital and acquired diseases affecting the aorta, relatively few entities affect the pulmonary trunk and/or the right and left main pulmonary arteries, and the frequency of these lesions is considerably lower than that for the aorta. Acquired nonneoplastic diseases of the pulmonary trunk and/or the main pulmonary arteries includes aneurysm, embolism, medial degeneration, dissection, arteritis, atherosclerosis, and trauma. These conditions alter the pulmonary trunk and the main pulmonary arteries by wall thinning or widening (aneurysm, medial degeneration), wall tearing or rupturing, narrowing (embolism), or various combinations of these. Of these conditions, luminal narrowing by 6, 1997 emboli is the most common. Congenital diseases of the pulmonary trunk and the main pulmonary arteries include stenosis, atresia, and aneurysm. General Considerations Normal Pulmonary 'hunk and Main Pulmonary ArteriesThe pulmonary trunk is defined as that segment of the pulmonary artery that arises from the right ventricular outtlow tract to its division to the right and left main pulmonary arteries. The length of the pulmonary trunk is about 4 to 5 cni. Its internal diameter ranges from 2 to 3 cm, and the thickness of the media is between 600 and 900 pm.2 Both diameter and medial thickness increase with advancing age.3 The right main pulmonary artery forms a right angle with the pulmonary trunk and follows a horizontal course posterior to the hilus. The left main pulmonary artery is a continuation of the trunk. The pulmonary hunk and its two main branches are elastic arteries. At the time of birth, the pulmonary trunk and the aorta have approximately the same medial thickness and the same dense layering of elastic fibers within the media. Within the first year of life, the ratio in thickness of the media of the pulmonary trunk to that of the aorta decreases to about 0.6.2~~ During the same period, the elastic configuration in the pulmonary trunk changes from that in the aorta. In the adult pulmonary trunk, the amount of elastic tissue per histologic unit of medial surface area is only 50 to 60% of that in the aorta.3 This implies that, although in the aorta the elastic layers are fairly regular and parallel and densely arranged, in the pulmonary trunk these layers are interrupted and are in iragments. The elastic fragments often appear swollen. The intiina of the pulmonary trunk and ...
This five-part review focuses on selected nonneoplastic diseases of the aorta and pulmonary trunk. Because many more diseases affect the aorta compared with the pulmonary trunk and right and left main pulmonary arteries, most of this review will be devoted to disorders of the aorta. Part I of this five-part review discusses general concepts of aorta anatomy and aortic dissection.
This five-part review focuses on selected nonneoplastic diseases of the aorta and pulmonary trunk. Because many more diseases affect the aorta compared with the pulmonary trunk and right and left main pulmonary arteries, most of this review will be devoted to disorders of the aorta. Part 111 of this five-part series discusses the etiology of aortic aneurysms and aortitis.
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