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(dĭ-sekt′) [L. dissecare, to cut up] To separate tissues and parts of a cadaver for anatomical study.


(dis-ek′ shŏn) [1dis- + section] 1. Separation of tissues with sharp instruments (sharp dissection) or blunt instruments (blunt dissection) along tissue planes during surgery or autopsy. 2. A surgical procedure to expose and excise certain tissues, e.g., regional lymph node dissection. 3. The ripping or tearing of a vascular structure, e.g., at a site of trauma or within an aneurysm.

aortic d. A life-threatening disruption of the aortic wall that causes blood to leave the true arterial lumen, either to enter a false lumen between the intima and the deeper layers of the vessel or to hemorrhage into the chest or abdomen.

 INCIDENCE: Between 5 and 30 people per 1, 000, 000 experience dissection of the aorta. Approx. 2000 cases are diagnosed in the U.S. annually.

 CAUSES: Aortic dissection usually occurs in patients with aneurysmal dilation of the aorta, but it may sometimes occur as a result of chest trauma, instrumentation or surgery on the thorax, congenital abnormalities of the aortic valve, connective tissue diseases, cocaine intoxication, or syphilis. Type A dissections involve the proximal aorta. They are more lethal than type B dissections, which involve the descending aorta. Dissections may induce tears in arteries that branch off from the main trunk of the aorta, into, for example, the carotid arteries, the renal arteries, or the intercostal arteries.

 SYMPTOMS AND SIGNS: Typical symptoms are sudden, severe chest pain, which may sometimes be described by patients as a ripping or tearing in quality rather than squeezing or oppressive as in angina pectoris. It may sometimes be associated with lower blood pressure in the left arm than in the right, and in some patients, a thrill may be felt overlying the sternal notch. It often results in sudden death.

 DIAGNOSIS: Dissection can be difficult to diagnose because of its resemblance to other forms of chest pain. It may be suggested by widening of the mediastinal shadow on routine chest x-ray, esp. if this is accompanied by visible separation of calcium from the outer wall of the aorta. It can be diagnosed with a variety of imaging studies, including transthoracic or transesophageal echocardiography, CT scanning with radiographic contrast or MR imaging of the chest. Aortography, the former criterion for diagnosis, is rarely employed now. Most patients with aortic dissection have an elevated serum D-dimer level (a low or normal D-dimer level excludes the disease in most instances).

 PREVENTION: Controllable risk factors for aortic dissection include hypertension, hyperlipidemia, smoking, and diabetes mellitus. Medical management of these conditions reduces the risk of dissection.

 TREATMENT: Many patients may be able to be stabilized ...

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