Which statement best describes the pathogenesis and histology distinguishing true abdominal aortic aneurysm from aortic dissection?

Which statement best describes the pathogenesis and histology distinguishing true abdominal aortic aneurysm from aortic dissection?

• A. True aneurysm: all three arterial layers dilated, wall weakened often with atherosclerosis; dissection: intimal tear with blood dissecting through the media, often with cystic medial degeneration.
• B. True aneurysm involves only the intima; dissection involves the adventitia; both lack degenerative changes.
• C. Both conditions involve only the media; dissection involves adventitial rupture; aneurysm never shows degeneration.
• D. Dissection is a chronic process with adventitial expansion; true aneurysm is an acute rupture risk.

Answer: (A)

The main idea is how the vessel wall fails and which layers are involved. A true aneurysm expands the entire vessel wall—intima, media, and adventitia—so the wall dilates while remaining a continuous, albeit weakened, structure. In the abdominal aorta this weakening is usually driven by atherosclerotic changes that compromise the media and the wall overall, leading to a circumferential dilation rather than a rupture. Aortic dissection, on the other hand, starts with a tear in the intima. Blood then penetrates into the media and splits the wall, creating a false lumen alongside the true lumen. Histologically, dissections commonly show degeneration of the media, such as cystic medial degeneration, which predisposes the wall to tearing and separation under pressure. So the statement is correct because it captures the essential contrast: true aneurysm involves dilation of all three wall layers with wall weakening often due to atherosclerosis; dissection begins with an intimal tear and blood dissects through the media, with medial degeneration frequently present. The other options misstate which layers are involved or the role of degeneration and the nature of the process.

The main idea is how the vessel wall fails and which layers are involved. A true aneurysm expands the entire vessel wall—intima, media, and adventitia—so the wall dilates while remaining a continuous, albeit weakened, structure. In the abdominal aorta this weakening is usually driven by atherosclerotic changes that compromise the media and the wall overall, leading to a circumferential dilation rather than a rupture.

Aortic dissection, on the other hand, starts with a tear in the intima. Blood then penetrates into the media and splits the wall, creating a false lumen alongside the true lumen. Histologically, dissections commonly show degeneration of the media, such as cystic medial degeneration, which predisposes the wall to tearing and separation under pressure.

So the statement is correct because it captures the essential contrast: true aneurysm involves dilation of all three wall layers with wall weakening often due to atherosclerosis; dissection begins with an intimal tear and blood dissects through the media, with medial degeneration frequently present. The other options misstate which layers are involved or the role of degeneration and the nature of the process.