ABDOMINAL AORTIC ANEURYSM
Posted by admin on May 12th, 2010The distal aorta is the site of the most common and most dangerous atherosclerotic aneurysms. They often involve the proximal common iliac arteries and rarely (< 2%) extend above the level of the renal arteries. These lesions almost always remain silent until they reach, or are close to. the point of rupture. An estimated 1 of 250 people > 50 yr die of a ruptured abdominal aortic aneurysm.
Symptoms, Signs, and Diagnosis
Most abdominal aneurysms can be detected by palpation. Thorough palpation of the abdominal aorta in the elderly is unQiiestionably one of the most important components of the physical examination. Typically, an aneurysm appears as an expansile mass that has both lateral and anterior pulsalions. However, often only a strong pulse is felt, making it difficult to distinguish the aneurysm from generalized ectasia and tortuosity. In persons of normal girth, the aortic pulse is generally palpable in the epigastrium. A strong pulse is normal in thin patients, whereas any pulse may signal an aneurysm in obese patients. About 50% of aneurysms are associated with a bruit.
Too often, the lesion is missed or is suspected only after an abdominal x-ray is taken for another reason. An anteroposterior view may indicate curvilinear aortic calcification near the midline, whereas a laleral film may outline ihe aneurysm’s calcified anterior and posterior walls.
Ultrasonography is the method of choice for confirming the diagnosis. It is virtually 100% accurate, providing precise information on the aneurysm’s size, shape, and location. The likelihood of rupture is directly related to the aneurysm’s transverse and anteroposterior diameters and inversely related to ils length. Rupture is not likely with diameters < 5 cm; thereafter, the rupture rate rises quickly. Abdominal aortic aneurysms have a much faster expansion rate than thoracic aortic aneurysms.
Initially, the rupture is usually a small perforation, blocked from leaking for hours or even days by pressure from a retroperitoneal blood clot. If it is diagnosed rapidly, lifesaving surgical repair may be possible. Unexplained abdominal or lower back pain with a prominent pulsation should suggest a ruptured aneurysm until proved otherwise. In an older obese patient, sudden pain suggests the diagnosis, even if a pulsation is undetectable.
In some cases, immediate exploratory laparotomy is indicated. However, if the index of suspicion is low and the onset of pain is recent, contrast CT of the abdomen can be performed. If the aneurysm has already ruptured, retroperitoneal swelling can usually be seen. Diagnosis of rupture is the only advantage a CT scan has over ultrasonography.
