AssessmentsAortic aneurysms and dissections: Clinical practice
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 66-year-old man presents to the emergency department with sudden onset sharp chest pain radiating to the back. The patient reports he has a history of long-standing hypertension, but he has not taken his medications in quite some time. His temperature is now 37.0°C (98.6°F), pulse is 120/min, respirations are 23/min, blood pressure is 85/60 mmHg, and oxygen saturation is 94% on room air. Physical examination shows 1+ peripheral pulses in the right upper extremity and 2+ pulses in the left upper extremity. Neurological examination shows 3/5 power in the left upper and lower extremities compared to 5/5 power in the right upper and lower extremities. Cardiovascular examination reveals muffled heart sounds. An ECG is obtained, which shows non-specific T-wave changes as well as electrical alternans. Non-contrast CT-brain is normal. Which of the following is the most appropriate definitive treatment for this patient’s condition?
Contributors:Evan Debevec-McKenney, Sam Gillespie, BSc, Rishi Desai, MD, MPH, Jake Ryan, Antonella Melani, MD, Kaia Chessen, MScBMC, Robyn Hughes, MScBMC
An aneurysm is a full-thickness dilation of a segment of a blood vessel so that it’s 50 percent greater than its normal diameter, and it’s usually caused by a weakness in the blood vessel wall.
True aneurysms involve all three layers of the arterial wall - the tunica intima, which has endothelial cells; the tunica media, which has smooth muscle; and the tunica adventitia, which has connective tissue as well as vasa vasorum which are the vessels nourishing the aortic wall itself.
There are two major types of aneurysms: fusiform aneurysms, which are uniform in shape with symmetrical dilatation and involves the entire circumference of the aortic wall; and saccular aneurysms, which are localized outpouchings of only a portion of the aortic wall.
Most individuals with Abdominal aortic aneurysm, or AAA, have no symptoms and are only detected as an incidental finding on imaging studies performed to evaluate an unrelated condition.
Some cases, especially in thinner individuals, may be discovered on a routine physical examination as a pulsating abdominal mass that can be felt on palpation and heard as a bruit on auscultation.
One-time screening with ultrasound can be done in individuals with risk factors like hypertension, increasing age, male gender, smoking, atherosclerosis, genetic syndromes - such as Turner syndrome or connective tissue diseases like Marfan’s syndrome or Ehlers-Danlos syndrome, familiarity for aneurysmal diseases, and having aneurysms in other arteries.
Blood may flow in between the layers of the blood vessel wall as the tear extends, which can lead to aortic rupture or decreased blood flow to the organs.
Dissection in most cases is associated with a sudden onset of severe pain, often described as tearing.
Aortic dissection can quickly evolve to full-thickness tearing due to the weakening of the aortic wall to the extent that it can no longer support the forces imposed upon it, leading to a complete rupture.
This may rapidly cause a massive hemorrhage, possibly evolving into shock and death.
A AAA is defined as dilation with a transverse diameter exceeding 3 centimeters.
Symptoms of a AAA, include abdominal pain that can radiate.
The pain is typically unrelated to movement or body position.
AAAs that cause symptoms may be about to rupture or may have already ruptured - and so all of them are considered medical emergencies.
Aneurysms cause turbulent blood flow and that can lead to vessel wall damage, areas of stagnant blood flow, and the formation of thrombi.
Thrombi can also embolize to various sites causing symptoms like claudication, painful blue digits due to recurrent focal ischemia - known as blue toe syndrome - or a painful pulseless cool extremity due to acute limb ischemia.
A definitive diagnosis of AAA requires seeing a focal aortic dilation on imaging.
Based on prior imaging, a rapidly expanding aneurysm is defined as one that grows more than 0.5 centimeters per year.
For symptomatic individuals, a diagnosis of AAA is guided by their hemodynamic status.
Hemodynamically stable individuals with symptoms of a AAA should get an urgent abdominal CT scan with contrast.
CT scan findings consistent with a ruptured AAA include a retroperitoneal hematoma, indistinct aortic walls, retroperitoneal fat stranding, loss of the fat plane between the aorta and surrounding tissue, and extravasation of IV contrast outside the aorta into the retroperitoneum, into a vein, or even into the bowel.
On the other hand, findings that may be associated with potentially unstable aneurysms or impending rupture include a crescent sign of layering hematoma within the aorta, aortic blebs that bulge from the surface of the aorta, "draping" of the aorta over a vertebral body, irregularity of the aortic wall, breaks in the calcification of the aortic wall, and localized areas of higher attenuation within a mural thrombus.
Now, in hemodynamically unstable individuals with symptoms of a AAA, they should be taken right away for surgical management.
On the other hand, if it’s not clear that they have an aneurysm, then a bedside ultrasound should be obtained.
The treatment options for asymptomatic AAA include conservative management, surveillance with a plan for eventual repair, and immediate repair.
Conservative treatment involves management of modifiable risk factors like smoking cessation, antihypertensive therapy to control blood pressure, statin therapy to lower cholesterol levels, and antiplatelet therapy for cardiovascular disease.
Asymptomatic AAA smaller than 5.5 centimeters in diameter should be followed up with annual ultrasound with periodic clinical evaluation and surveillance of aneurysm diameter.
Repair is recommended if the aneurysm is or becomes bigger than 5.5 centimeters or is rapidly expanding, which is defined as an increase in maximal aortic diameter of 5 millimeters or more over a six-month period of time or more than 1 centimeter over one year.
For a symptomatic unruptured AAA of any size, urgent AAA repair should be performed, because the presence of symptoms suggests that the aneurysm is rapidly changing and might rupture.
A ruptured AAA can be fatal and needs emergency repair.
For individuals with ruptured AAA, the systolic blood pressure should be maintained between 80 and 100 mm Hg prior to repair, which is known as permissive hypotension, to minimize further tearing of the aorta and reduce blood loss.
There are two modes of repair: open aneurysm repair, and endovascular aneurysm repair or EVAR.
The dilated portion of the aorta is opened for insertion of a synthetic graft.