The term dissecting aneurysm is applied for a dissecting haematoma in which the blood enters the separated (dissected) wall of the vessel and spreads for varying distance
longitudinally. The most common site is the aorta and is an acute catastrophic aortic disease. The condition occurs most
commonly in men in the age range of 50 to 70 years. In women, dissecting aneurysms may occur during pregnancy.
PATHOGENESIS.
The pathogenesis of dissecting aneurysm is explained on the basis of weakened aortic media. Various conditions causing weakening in the aortic wall resulting in dissection are as under:
i) Hypertensive state. About 90% cases of dissecting aneurysm have hypertension which predisposes such patients to degeneration of the media in some questionable way.
ii) Non-hypertension cases. These are cases in whom there is some local or systemic connective tissue disorder.
e.g.
a) Marfan’s syndrome, an autosomal dominant disease with genetic defect in fibrillin which is a connective tissue protein
required for elastic tissue formation.
b) Development of cystic medial necrosis of Erdheim, especially in old age.
c) Iatrogenic trauma during cardiac catheterisation or coronary bypass surgery.
d) Pregnancy, for some unknown reasons.
Once medial necrosis has occurred, haemodynamic factors, chiefly hypertension, cause tear in the intima and initiate the dissecting aneurysms. The media is split at its weakest point by the inflowing blood. An alternative suggestion is that the medial haemorrhage from the vasa vasorum occurs first and the intimal tear follows it. Further
extension of aneurysm occurs due to entry of blood into the media through the intimal tear.
EFFECTS.
The classical clinical manifestation of a dissecting aneurysm is excruciating tearing pain in the chest moving downwards. The complications arising from dissecting
aneurysms are as under:
1. Rupture. Haemorrhage from rupture of a dissecting aneurysm in the ascending aorta results in mortality in 90% of cases. Most often, haemorrhage occurs into the; pericardium less frequently it may rupture into thoracic cavity, abdominal cavity or retroperitoneum.
2. Cardiac disease. Involvement of the aortic valve results in aortic incompetence. Obstruction of coronaries results in ischaemia causing fatal myocardial infarction. Rarely, dissecting aneurysm may extend into the cardiac chamber.
3. Ischaemia. Obstruction of the branches of aorta by dissection results in ischaemia of the tissue supplied. Thus, there may be renal infarction, cerebral ischaemia and infarction of the spinal cord.
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