An 89-year-old woman presents to the ED complaining of severe abdominal pain radiating to the rectum and back, which started suddenly while walking up the stairs that day. She feels “tired” and dizzy, but denies nausea, vomiting, constipation, melena, chest pain, hematuria, syncope, paresthesias, or focal weakness.
Her past medical history is significant for coronary artery disease, bilateral carotid stents, and hypertension. In the ED, she is hypotensive, 83/62 mmHg. The bedside ultrasound reveals free fluid and an aortic diameter of 8 cm.
What is the diagnosis and management of this condition?
Diagnosis: Ruptured AAA
Abdominal aortic aneurysm (AAA) is defined as having an aortic diameter greater than 3 cm, although a diameter of greater than 4 cm is considered clinically significant. A ruptured AAA is the great masquerader, a true intra-abdominal emergency requiring prompt recognition and intervention, and the 10th most common cause of death for adults over 55. (J Vasc Surg 1984;1:6.) Patients presenting with symptomatic AAAs can mimic renal and biliary colic, bowel angina from mesenteric ischemia, lumbosacral disc disease, pancreatitis, gastrointestinal bleeding, colitis, diverticulitis, cardiac ischemia, and pyelonephritis, resulting in misdiagnosis in nearly a third of cases. (J Vascl Surg 1992; 16:17.)
The abdomen is the most common site of arterial aneurysm, and is often found between the takeoff of the renal and inferior mesenteric arteries. An estimated one percent of men over 55 have a AAA (>4 cm), according to screening investigations (Ann Intern Med 1997; 126:441], with an increasing incidence of two to four percent per decade of life. (Am J Epidemiol 2001;154:236.) The etiology and pathophysiology of AAAs are not completely understood, and it is unclear if atherosclerosis is the cause or consequence of arterial dilatation.
Recent studies show that genomic predisposition may play a role in some patients. (Am J Surg 1984;147:551.) Studies also have identified the possible role of proteases including plasmin, matrix metalloproteinases, cathepsin, and pro-inflammatory mediators, including C-reactive protein, and cytokines (interleukin (IL)-6) in the pathogenesis of AAA development and rupture.
Significant risk factors for AAA include smoking (strongest predictor [Ann Intern Med 1997;126(6):441]), male sex, and age over 55. Other risk factors include a family history (particularly in first-degree relatives) or personal history of hypertension, lower extremity aneurysm, Caucasian race, salmonella or syphilis infection, atherosclerosis or peripheral vascular disease, and Marfan or Ehlers-Danlos syndrome.
Most AAAs do not rupture, but when they do, the result is mortality higher than 50 percent, rate with patients dying quickly from exsanguination into the intra- or retroperitoneal space. Risk factors for rupture include female gender, aneurysm diameter, rapid rate of expansion, uncontrolled hypertension, and active smoking. The risk of rupture of a 4 to 4.9 cm aneurysm is less than five percent compared with a risk of a 30 to 50 percent of aneurysms larger than 8cm. (J Vasc Surg 2003;37:1106.)
Ideally the diagnosis of AAA would be made prior to a patient developing clinical symptoms. Most patients with intact AAAs are found incidentally on diagnostic imaging for other purposes via ultrasound, abdominal computerized tomography, magnetic resonance imaging, or occasionally on radiographs if well calcified. The rate of development of a AAA after a negative abdominal ultrasound at age 65 is negligible (1% in five years), which has led some researchers to call for one abdominal ultrasound for all at-risk patients 65 and older to rule out AAA. (Br J Surg 1994;81:1112.)
Patients with a known AAA who present with clinical symptoms including abdominal, flank, or back pain are worrisome for aneurysm expansion, and are at increased risk of rupture. Patients with large AAAs may have a palpable abdominal pulsatile mass just superior to the umbilicus (the aorta bifurcates at the umbilicus), with a bruit appreciated on auscultation. Smaller aneurysms and large body habitus or abdominal panus may make these difficult to appreciate, however, with reported total sensitivity and specificity of the physical exam being 30 to 75 percent depending on the size of the aneurysm. (JAMA 1999;281:77.)
Patients with ruptured AAA who survive long enough to make it to the ED for evaluation classically present with abdominal or back pain and hemorrhagic shock. Prompt evaluation and treatment is critical, and should follow standard resuscitation protocols including blood product transfusion with rapid surgical evaluation and treatment.
The gold standard for screening for AAA is ultrasound, which is technically simple to perform at the bedside in the ED, is within the scope of practice for EPs, does not expose the patient to harmful radiation, and has high sensitivity reaching nearly 100 percent. (Am J Roentgenol 1989;152:785.) It also can quickly identify intraperitoneal blood from AAA rupture, but ultrasound cannot specifically identify aneurismal rupture, and is not ideal for evaluating for complications such as renal or visceral artery involvement. (N Engl J Med 1993; 328:1167.) At times body habitus or bowel gases can obscure visualization.
In patients for whom a concern for rupture exists, CT with intravenous contrast is necessary to demonstrate extravasation from the aorta and identify possible hemorrhage or hematoma (as seen in the picture). Retroperitoneal bleeding is seen in 76 to 90 percent of cases, and is typically on the left side. (Surg Clin N Am 1989;69:859.) MRI also can accurately demonstrate AAAs, but has a limited role in the acute setting when rupture is considered because of the length of the study to be completed and the limited availably in many hospitals.
As radiological modalities become more sophisticated, more patients are being identified with early AAAs. This presents a therapeutic dilemma given that many patients who are found to have an AAA are poor elective surgical candidates. The five-year risk of rupture for AAA less than 4 cm is negligible. (N Engl J Med 1989;321:1009.) Appropriate selection and timing of treatment for identified incidental aneurysms remains somewhat controversial, and includes early operative repair, endovascular stenting, and “watchful waiting.” (JAMA 1992;268:2678.)
Once rupture occurs, emergent repair is indicated. Current guidelines recommend elective repair of intact aneurysms larger than or equal to 5.5 cm (Circulation 2006;113:e463) and possibly of symptomatic aneurysms, aneurysms greater than twice the original abdominal aortic diameter, those with rapidly increasing diameter, aneurysms with thoracic or suprarenal aortic segment involvement, or those with femoral or iliac involvement. Endovascular repair may be more appropriate for patients with significant co-morbid conditions where open surgical repair may be considered more high risk to the patient. For AAAs 3 cm to 4.5 cm, serial imaging studies are recommended (“watchful waiting”), in addition to smoking cessation and optimization of blood pressure (including the use of beta blockers) and lipid profiles per standard guidelines.
This patient was taken to the operating room emergently, and survived to hospital discharge.
Thanks to Daniel Theodoro, MD, for the ultrasound image appearing with the first part of this article.