Page 423 - Textbook of Pathology, 6th Edition

adventitia, followed by endarteritis obliterans. This results ii) Non-hypertensive cases. These are cases in whom there 407
in ischaemic injury to the media causing destruction of the is some local or systemic connective tissue disorder e.g.
smooth muscle and elastic tissue of the media and scarring. a) Marfan’s syndrome, an autosomal dominant disease with
Since syphilitic aortitis involves the proximal aorta genetic defect in fibrillin which is a connective tissue protein
maximally, aortic aneurysm is found most frequently in the required for elastic tissue formation.
ascending aorta and in the aortic arch. b) Development of cystic medial necrosis of Erdheim, especially
in old age.
MORPHOLOGIC FEATURES. Syphilitic aneurysms c) Iatrogenic trauma during cardiac catheterisation or
occurring most often in the ascending part and the arch coronary bypass surgery.
of aorta are saccular in shape and usually 3-5 cm in d) Pregnancy, for some unknown reasons.
diameter. Less often, they are fusiform or cylindrical. The Once medial necrosis has occurred, haemodynamic
intimal surface is wrinkled and shows tree-bark appearance. factors, chiefly hypertension, cause tear in the intima and
When the aortic valve is involved, there is stretching and initiate the dissecting aneurysms. The media is split at its
rolling of the valve-leaflets producing valvular weakest point by the inflowing blood. An alternative
incompetence and left ventricular hypertrophy due to suggestion is that the medial haemorrhage from the vasa
volume overload. This results in massively enlarged heart vasorum occurs first and the intimal tear follows it. Further
called ‘cor bovinum’. extension of aneurysm occurs due to entry of blood into the
Histologically, the features of healed syphilitic aortitis are media through the intimal tear.
seen (page 401). The adventitia shows fibrous thickening
with endarteritis obliterans of vasa vasorum. The fibrous MORPHOLOGIC FEATURES. Dissecting aneurysm
scar tissue may extend into the media and the intima. differs from atherosclerotic and syphilitic aneurysms in
Rarely, spirochaetes may be demonstrable in syphilitic having no significant dilatation. Therefore, it is currently
aneurysm. Often, mural thrombus is found in the referred to as ‘dissecting haematoma’. Dissecting aneurysm
aneurysm. classically begins in the arch of aorta. In 95% of cases, there
is a sharply-incised, transverse or oblique intimal tear, 3-
EFFECTS. The clinical manifestations are found much more 4 cm long, most often located in the ascending part of the CHAPTER 15
frequently in syphilitic aneurysms than in atherosclerotic aorta. The dissection is seen most characteristically
aneurysms. The effects include the following: between the outer and middle third of the aortic media so
that the column of blood in the dissection separates the
1. Rupture. Syphilitic aneurysm is likely to rupture causing intima and inner two-third of the media on one side from the
massive and fatal haemorrhage into the pleural cavity, outer one-third of the media and the adventitia on the other.
pericardial sac, trachea and oesophagus.
The dissection extends proximally into the aortic valve
2. Compression. The aneurysm may press on the adjacent ring as well as distally into the abdominal aorta
tissues and cause symptoms such as on trachea causing (Fig. 15.17).
dyspnoea, on oesophagus causing dysphagia, on recurrent Occasionally, the dissection may extend into the
laryngeal nerve leading to hoarseness; and erosion of branches of aorta like into the arteries of the neck, coro-
vertebrae, sternum and ribs due to persistent pressure. naries, renal, mesenteric and iliac arteries. The dissection
3. Cardiac dysfunction. When the aortic root and valve are may affect the entire circumference of the aortic media or
involved, syphilitic aneurysm produces aortic incompetence a segment of it. In about 10% of dissecting aneurysms, a The Blood Vessels and Lymphatics
and cardiac failure. Narrowing of the coronary ostia may second intimal tear is seen in the distal part of the
further aggravate cardiac disease. dissection so that the blood enters the false lumen through
the proximal tear and re-enters the true lumen through
Dissecting Aneurysms and Cystic Medial Necrosis the distal tear. If the patient survives, the false lumen may
develop endothelial lining and ‘double-barrel aorta’ is
The term dissecting aneurysm is applied for a dissecting formed.
haematoma in which the blood enters the separated Two classification schemes for dissections of thoracic
(dissected) wall of the vessel and spreads for varying distance aorta and intramural haematoma have been described
longitudinally. The most common site is the aorta and is an (Fig. 15.18):
acute catastrophic aortic disease. The condition occurs most I. DeBakey classification. Depending upon the extent of
commonly in men in the age range of 50 to 70 years. In aortic dissection, three types are described:
women, dissecting aneurysms may occur during pregnancy. Type I: Comprises 75% of cases; the intimal tear begins in
PATHOGENESIS. The pathogenesis of dissecting aneurysm the ascending aorta but dissection extends distally for
is explained on the basis of weakened aortic media. Various some distance.
conditions causing weakening in the aortic wall resulting in Type II: Comprises 5% of cases and dissection is limited
dissection are as under: to the ascending aorta.
Type III: Constitutes the remaining 20% cases. In these
i) Hypertensive state. About 90% cases of dissecting cases, intimal tear begins in the descending thoracic aorta
aneurysm have hypertension which predisposes such near the origin of subclavian artery and dissection extends
patients to degeneration of the media in some questionable distally.
way.