Dissecting Aneurysms

The ischemic end-organ manifestations associated with many dissections may confuse the differential diagnosis, which includes myocardial infarction, pericardial disease, pulmonary disorders, stroke, musculoskeletal disease of the extremities, spinal cord injuries, and intraabdominal disorders. Ischemic manifestations may change with time (as the dissection progresses) distracting the physician from making the correct diagnosis. Rupture of the dissection into the true lumen may cause a cessation of symptoms, and the correct diagnosis may then be inappropriately dismissed.

Thoracic dissecting aneurysms will most commonly (90 percent) have an abnormal aortic contour on chest x-ray. Widening of the mediastinum and deviation of the trachea, mainstem bronchi, or esophagus may also be seen (Fig 54-2 and Fig 54-3). Intimal calcium may be visible and distant from the edge of the aortic contour

(calcium sign).

CT scanning may reliably make the diagnosis of aortic dissection ( Fig 54-4).1 I3 Sensitivity for dissection ranges from 83 to 100 percent and specificity ranges from

87 to 100 percent.12 Spiral CT with rapid intravenous boluses of contrast may be more sensitive.13 However, CT scan cannot reliably give anatomic details of other arterial branches off the aorta and cannot address aortic valve competence.

FIG. 54-4. Computed tomographic scan of same patient revealing false (double arrows) and true aortic lumens in both ascending and descending aorta.

Angiography can be considered the "gold standard" for diagnosis and will provide more anatomic detail than a CT scan. 113 Aortography also will reliably show complications of dissection, including involvement of branch vessels, aortic valve incompetence, and coronary artery involvement. However, the angiogram is not a perfect study. Erbel14 found aortography to have a specificity of 94 percent and a sensitivity of 88 percent. Risks of the procedure include the use of intravenous contrast agents and the delay in assembling an angiography team.

In experienced hands, a transesophageal echocardiogram (TEE) may be as sensitive and specific as angiography. 1516 and H Sensitivity for dissection ranges from 97 to 100 percent, specificity 97 to 99 percent.12 Some 3 percent of patients cannot tolerate the procedure, which should be performed under sedation or general anesthesia. Known esophageal disease is a relative contraindication. Disruption of sound transmission by air in the trachea or left bronchi may cause difficulty in evaluating the ascending aorta. Among the imaging techniques mentioned above, TEE has the highest diagnostic variability between operators or observers. Therefore, the imaging procedure of choice may vary between institutions. 12 In contrast with AAAs, suspected dissections must be confirmed radiologically prior to operative repair.

Thoracic aortic saccular aneurysms are generally uniformly identified on chest x-ray. Rarely, the presence of thoracic, pleural, or parenchymal densities may make the diagnosis more difficult. CT scan will delineate these aneurysms reliably.

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