Aortic dissection is a medical emergency and usually presents with pain of very sudden onset accompanied by a tearing sensation. However patients frequently present with vague and less specific symptoms, as in this case. The most important risk factor for aortic dissection is hypertension (60-90%). Other predisposing conditions are Marfan's syndrome, Ehlers-Danlos syndrome, relapsing polychondritis, valvular aortic stenosis, Turner's syndrome, Behcet's disease, coarctation, pregnancy, aortitis and trauma. At risk patients usually have some form of dilating aortopathy.
Until recently it was thought that the initial event in dissection was an intimal tear, causing extravasation of blood in the media from the point of intimal rupture, and demonstration of an intimal flap was considered to be essential to make a diagnosis. It is now recognised that the process often begins as intramural haematoma. Degeneration of the media leads to rupture of the vasa vasorum with bleeding into the media. This may subsequently heal or more often, especially in the ascending aorta, progresses to full dissection with an intimal flap.
Dissections are divided by the Stanford classification into Type A and Type B. Type A involves the ascending aorta and Type B begins distal to the origin of the left subclavian artery. 70% of dissections are Type A and carry high mortality due to the risk of rupture into the pericardium causing tamponade, acute aortic regurgitation and dissection into the coronary or brachiocephalic arteries. Type B dissections have a more benign course and are often managed conservatively. An alternative classification of dissections into 3 types by DeBakey is not in very wide use.
Imaging investigations depend on the clinical situation. Aortography was earlier considered to be the gold standard but now has no place in investigation. Depending on the availability and expertise, echocardiography (TTE and TEE), CT and MR may be used, after a chest radiograph has been obtained.
Chest X-rays may be normal (25%) or may show a widened mediastinum, inward displacement by more than 1cm of atherosclerotic plaque from the aortic contour, indistinct outline of the aorta, cardiomegaly due to pericardial effusion/ventriculomegaly, and pleural effusion. TTE shows the aortic root and aortic valve well, but the arch is not well seen. TEE has very high sensitivity and specificity in expert hands. Spiral CT may show an intimal flap separating two aortic channels, internally displaced intimal calcification and a crescentic high attenuation clot in the false lumen. MRI is particularly good at showing early intramural haematoma. Standard ECG gated spin echo shows dissections and intramural thrombus well. Faster sequences like rapid breath hold MRI and breath hold 3D MRA (with or without contrast enhancement) allow faster and more comprehensive examination of the aorta.