Chapter 27. Aortic Dissection and Aneurysms

Aortic dissection and abdominal aortic aneurysms (AAAs) are important causes of morbidity and death that require rapid diagnosis and frequently require prompt operative repair to offer the patient any chance of survival. Diagnosing these conditions can be challenging and carries a high risk of misdiagnosis.

Clinical Features

Four clinical scenarios arise regarding AAAs: acute rupture, aortoenteric fistula, chronic contained rupture, and an incidental finding. Although there are several other nonaortic large artery aneurysms that often require surgical repair by a vascular surgeon, they are aptly covered in Tintinalli's Emergency Medicine, 7th edition.

Acute rupturing AAA is a true emergency that, if not rapidly identified and repaired, will lead to death. The classic presentation is of an older (>60 years) male smoker with atherosclerosis who presents with sudden onset severe back or abdominal pain, hypotension, and a pulsatile abdominal mass. Patients may present with syncope or some variation of unilateral flank pain, groin pain, hip pain, or pain localizing to one quadrant of the abdomen.

Fifty percent of patients describe a ripping or tearing pain that is severe and abrupt in onset. Patients may have a tender pulsatile abdominal mass on physical examination, but the absence of pain does not imply an intact aorta. Obesity may mask a pulsatile abdominal mass. Nausea and vomiting are commonly present.

Shock may persist through presentation or may transiently improve due to compensatory mechanisms. Femoral pulsations are typically normal. Retroperitoneal hemorrhage may be appreciated as periumbilical ecchymosis (Cullen sign), flank ecchymosis (Grey-Turner sign), or scrotal hematomas. If blood compresses the femoral nerve, a neuropathy of the lower extremity may be present.

Aortoenteric fistulas, although rare, present as gastrointestinal bleeding, either a small sentinel bleed or massive life-threatening hemorrhage. A history of previous aortic grafting (eg, AAA repair) increases the suspicion. Because the duodenum is the usual site of the fistula, the patient may present with hematemesis, melenemesis, melena, or hematochezia.

Chronic contained rupture of AAA is an uncommon presentation. If an AAA ruptures into the retroperitoneum, there may be significant fibrosis and a limiting of blood loss. The patient typically appears quite well and may complain of pain for an extended period.

Discovering a previously undiagnosed asymptomatic AAA on physical or radiologic examination can be lifesaving. Those aneurysms larger than 5 cm in diameter (outer wall to outer wall) are at a greater risk for rupture, but all should be referred to a vascular surgeon.

Diagnosis and Differential

Although the diagnosis may be relatively straightforward in the setting of syncope, back pain, and shock with a tender pulsatile abdominal mass, the differential diagnosis varies depending on the presentation. Missed AAAs are most frequently misdiagnosed as renal colic. This life-threatening disease process should be considered in the differential diagnosis for any patient that presents with back pain, an intraabdominal process (pancreatitis, diverticulitis, mesenteric ischemia, etc), possible testicular torsion, or gastrointestinal bleeding disorders (eg, esophageal varices, tumors, or ulcers).

If the diagnosis of rupturing AAA is clear on clinical grounds, the operating vascular surgeon should immediately evaluate the patient. However, when the diagnosis is not entirely clear, confirming studies may be required. In the unstable patient, technically adequate bedside abdominal ultrasound has a >90% sensitivity for identifying AAA and can measure the diameter of the aneurysm (see Fig. 27-1). Be aware that aortic rupture or retroperitoneal bleed cannot be reliably identified with ultrasound. Obesity and bowel gas technically may limit the study. In the stable patient, computed tomography (CT) can identify the AAA and delineate the anatomic details of the aneurysm and any associated rupture. The role of plain radiography in the diagnosis of rupturing AAA in unclear; a calcified, bulging aortic contour is present in only 65% of patients with symptomatic AAA.

Emergency Department Care and Disposition

The primary role of the emergency physician is in identifying AAA.

1. For suspected rupturing AAA or aortoenteric fistula, prompt surgical consultation in anticipation of emergency surgery is critical. No diagnostic testing should delay surgical repair.

2. The patient is stabilized with large-bore intravenous access, judicious fluid administration for hypotension, treatment of hypertension (see Chapter 26), and typing and cross-matching of several units of packed red blood cells, with transfusion as needed. Because patients may rapidly deteriorate, those who undergo diagnostic testing should not be left unattended in the radiology department.

3. Pain control should be initiated with narcotic medications as compared to nonsteroidals due to medication induced platelet dysfunction. Control of pain is a compassionate intervention that may aid in control of blood pressure, but beware of hypotension.

4. For chronic contained rupturing AAA, consultation with a vascular surgeon for urgent repair and intensive care unit admission should be sought.

5. For AAA identified as an incidental finding, the patient potentially can be discharged home, depending on the aneurysmal size and comorbid factors. Telephone consultation with a vascular surgeon for admission or close office follow-up is usually adequate.

Clinical Features

Aortic dissection typically presents (>85% of patients) with acute onset of pain that is most severe at onset located in the chest and radiating to the back. The location of the pain may indicate the area of the aorta that is involved. Seventy percent of patients with ascending involvement have anterior chest pain, and 63% of patients with involvement of the descending aorta have back pain. The pain pattern may change as the dissection progresses from one anatomic area to another. The pain is described as ripping or tearing by 50% of patients. Accompanying nausea, vomiting, diaphoresis and the feeling of impending doom are common.

Most patients are male (66%), older than 50 years (mean age, 63), and have a history of hypertension (72%). Another group of patients are younger with identifiable risk factors such as connective tissue disorders, congenital heart disease, and pregnancy. Up to 30% of patients with Marfan syndrome will develop a dissection. Iatrogenic induced aortic dissection may occur after aortic catheterization or cardiac surgery.

To communicate more effectively with the surgeons, the emergency department physician should classify aortic dissections in 1 of 2 ways. The Stanford classification divides dissections into those that involve the ascending aorta (type A) and those that are restricted to the descending aorta (type B). The DeBakey classification divides dissections into 3 groups: involvement of the ascending and descending aortas (type I), involvement of only the ascending aorta (type II), or involvement of only the descending aorta (type III). Also look for an intramural hematoms, due to infarction of the aortic media, that may resolve or progress onto a true dissection.

As the dissection progresses, seemingly unrelated symptom complexes may present themselves. Presentations include aortic valve insufficiency, coronary artery occlusion with myocardial infarction, carotid involvement with stroke symptoms, occlusion of vertebral blood supply with paraplegia, cardiac tamponade with shock and jugular venous distention, compression of the recurrent laryngeal nerve with hoarseness of the voice, and compression of the superior cervical sympathetic ganglion with Horner syndrome. The dissection may open back into the true aortic lumen with a marked decrease in symptoms, leading to a false sense of security.

The patient's physical examination findings will depend on the location and progression of the dissection. A diastolic murmur of aortic insufficiency may be heard. Hypertension and tachycardia are common, but hypotension also may be present. Fifty percent of patients have decreased pulsation in the radial, femoral, or carotid arteries. Although one might expect a difference in extremity blood pressures, no specific threshold values have been defined. Forty percent of patients have neurologic sequelae.

Diagnosis and Differential

The differential diagnosis to be considered depends on the location and progression of the dissection. Other causes of aortic insufficiency, myocardial infarction, esophageal rupture, other causes of strokes, spinal injury or tumor, vocal cord tumors, and other causes of cardiac tamponade, including pericardial disease, may need to be considered. An electrocardiogram would help demonstrate disruption of a coronary artery, most commonly the right.

The diagnosis of aortic dissection depends on radiographic confirmation once the diagnosis is suspected. The chest x-ray is abnormal in 80% of patients with aortic dissection. The abnormality may be an abnormal aortic contour; widening of the mediastinum; deviation of the trachea, mainstem bronchi, or esophagus; apical capping; or pleural effusion. The “calcium sign” may be present, with intimal calcium deposits seen distant from the edge of the aortic contour. CT is 83% to 100% sensitive and 87% to 100% specific for the diagnosis of dissection. Spiral CT with rapid IV contrast boluses is the most sensitive (see Fig. 27-2). Angiography is rarely used anymore. It may better define the anatomy, extent, and complications of a dissection. Transesophageal echocardiograms, in experienced hands, are 97% to 100% sensitive and 97% to 99% specific. The use of these studies is institutionally dependent, and they should be ordered in conjunction with the consulting vascular or thoracic surgeon.

Emergency Department Care and Disposition

All patients with aortic dissection or strongly suspected aortic dissection require emergent vascular or thoracic surgical consultation and prompt radiographic confirmation of the diagnosis, which is best directed by the operating surgeon. In general, patients with dissection of the ascending aorta require prompt surgical intervention. The operative care of dissection of only the descending aorta is controversial and should be evaluated on a case-by-case basis.

1. Stabilization of the patient typically requires large-bore intravenous access with availability of type and cross-matched blood in case of free rupture.

2. Management of hypertension is best done with β-blockers because these decrease the blood pressure and the shear force (see Chapter 26). Agents such as esmolol (300 micrograms/kilogram IV bolus followed by a 50 micrograms/kilogram/min infusion) or labetolol (20 milligrams IV for 2 min followed by subsequent doses of 20 to 40 milligrams IV for 10 min) are typically used. The goal is to reduce heart rate to between 60 and 70.

3. Vasodilators, such as nitroprusside (starting at 0.3 micrograms/kilogram/min IV), should be used only after adequate inotropic blockade has been made with β-receptor or calcium-channel blockers (see Chapter 26). Intravenous antihypertensive therapy in an acute aortic dissection is traditionally titrated according to pain relief and BP with a final goal of achieving a systolic BP of 100 to 120 mm Hg. Even lower levels of systolic BP may be required as long as vital organs (brain, heart, kidneys) maintain adequate perfusion.