Thoracic aortic dissection occurs when the intima of the aorta becomes compromised and “tears” or “dissects” a new layer that fills with blood between the intima and the media. This “false lumen” can start in different locations and has variable propagation. The most common predisposing factor for aortic dissection is hypertension. While ascending aortic dissection is a surgical emergency, a descending aortic dissection can be treated medically in most cases.
There are two classification systems used to describe thoracic aortic dissections:
The DeBakey classification:
Type I: Dissection originating in the ascending aorta extending a variable length frequently into the aortic arch and/or descending thoracic aorta
Type II: Dissection originating in the ascending aorta remaining confined to this area.
Type III: Dissection originating in the descending thoracic aorta. This is further classified as IIIa which is confined to the thoracic aorta and IIIb which extends to the abdominal aorta.
The Stanford classification:
Type A: Dissection involving any part of the ascending aorta
Type B: Dissection remaining confined to the descending thoracic aorta
When the intima becomes compromised, a tear can occur leading to dissection, however it is well known that pathology of the aortic media is involved as well and is a prerequisite in most non-traumatic aortic dissections. Connective tissue disorders such as Marfan’s syndrome have a significantly increased risk of aortic dissection.
By J Heuser
The onset of symptoms in aortic dissection are usually sudden without warning. While pain of an ascending aortic dissection frequently is in the center of the chest radiating to the mid upper-thoracic area, the pain from descending dissection is usually localized to the back sometimes radiating to the abdomen. The pain is frequently described as “sharp” or “tearing” in nature and is quite severe in intensity. Uncontrolled hypertension is frequently present at the time of descending aortic dissection. Rarely, spinal ischemia from compromise of the intercostal arteries can occur causing paraplegia that is usually irreversible.
The physical examination is non-specific for descending thoracic aortic dissection, but a pulse deficit can be seen if the iliac arteries are involved. The blood pressure is frequently elevated. Renal artery bruits may be present if there is involvement of that vessel.
Since rapid diagnosis is crucial in ascending aortic dissections and the presentation of descending dissection are similar, the clinician must always have a high index of suspicion which is based on the patient’s clinical presentation and symptoms.
Chest x-ray can show mediastinal widening and/or an abnormal aortic contour. Computed tomography (CT) is the definitive diagnostic modality and has a sensitivity approaching 100%. Transesophageal echocardiography and MRI can be useful as well.
Descending aortic dissections can be treated medically. The goal of medical therapy is aimed at reducing blood pressure and the shear force on the aorta. Beta-blockers with some alpha blocking properties (carvedilol, labetalol) are commonly used with a goal systolic blood pressure < 120 mmHg. Calcium channel blockers and nitrates can also be helpful. Surgical treatment is indicated if the dissection causes end-organ ischemia (renal or mesenteric infarction) or rupture into the retroperitoneal space which can be life threatening.