Skip to content
Explore atlas
PH-CV08

Aortic aneurysm and dissection

How the elastic wall of the aorta weakens, why a weakened segment balloons and keeps growing until it may rupture, and how a tear in the inner wall lets blood split the layers apart in an aortic dissection.

By the end, you can

  • Describe the aorta’s course and the structure of its wall.
  • Explain how degeneration of the media weakens the aortic wall and lets it dilate.
  • Use the law of Laplace to explain why aneurysms tend to grow faster as they enlarge.
  • Explain how an intimal tear produces a dissection with a false lumen.
  • Relate the symptoms of rupture and dissection to blood loss and branch artery occlusion.
  • Recognise the classic appearances, classifications and tests of aortic aneurysm and dissection, and explain how blood-pressure control and repair act on the mechanism.

What it is

An aortic aneurysm is a permanent, localised dilatation of the aorta, conventionally to at least 1.5 times its normal diameter (for the abdominal aorta, 3 cm or more). An aortic dissection is a tear in the aorta’s inner layer that lets blood track between the layers of its wall, creating a second, false channel. Both can rupture and are medical emergencies when they do.

3 types to tell apart
Abdominal aortic aneurysm
The commonest aneurysm, usually below the renal arteries; linked to age, smoking, male sex and family history.
Thoracic aortic aneurysm
Often in the ascending aorta; linked to hypertension, a bicuspid aortic valve and inherited connective tissue disorders.
Dissection: ascending (type A) and descending (type B)
Dissections involving the ascending aorta are the most immediately dangerous; those confined to the descending aorta behave differently.

US spelling: fibres → fibers.

Normal function

The aorta and its elastic wall

The aorta leaves the left ventricle as the , arches over the heart (the , giving off the branches to the head and arms) and descends through the chest as the , continuing through the abdomen to divide into the iliac arteries.

Its wall has three layers, like other arteries: a thin intima, a thick media and an outer adventitia. Unlike a muscular artery, the aortic media is packed with dozens of layers of elastic fibres with smooth muscle and collagen between them.

With each heartbeat the elastic wall stretches to absorb the surge of blood, then recoils to keep blood flowing in diastole. Collagen sets the wall’s ultimate strength, stopping it from stretching too far.

Point to it on the model