Sharon A. Cranford
Professor Alice Bailey and Professor Jill Millard
November 6, 2007
There are several areas that a sonographer must address when evaluating the major aortic artery. A potentially life threatening condition that may arise within the aorta is an aneurysm. This paper will explain two types of abdominal aortic aneurysms: fusiform and saccular. This paper will also address several questions relating to aneurysms such as symptoms of the disease, imaging diagnosis, lab values, and treatment of the disease as well as prognosis of aneurysms.
Fusiform and Saccular Aortic Aneurysms
An important function of vascular ultrasound includes the evaluation of the major vessels of the body. The sonographer must be able to recognize abnormalities represented in diagnostic imaging. Two abnormalities of the abdominal aorta include the fusiform and saccular aneurysm. This research paper will present in detail and explain abdominal aortic aneurysms by including the answers to the following questions:
- What is an abdominal aortic aneurysm?
- What are the symptoms of an aneurysm?
- What are the lab values associated with aneurysms?
- What imaging diagnosis is relevant to aneurysms?
- What is the treatment and prognosis for an aneurysm?
After answering these questions regarding abdominal aortic aneurysms and specifically fusiform and saccular types, the reader will have a better understanding of what is involved with aneurysms and how this disease is represented in diagnostic imaging and other diagnostic tests.
By definition from Taber’s Cyclopedic Medical Dictionary, (2005): Aneurysm is a “localized abnormal dilatation of a blood vessel, usually an artery; due to a congenital defect or weakness in the wall of the vessel” (p. 113). Aortic aneurysms refer specifically to the aorta and can occur at any point along the aortic wall. Due to the constant pressure from the arterial blood flow within the artery, the weakened medial layer of the vessel becomes enlarged (Aneurysm, 2002).
Enlargement of the vessel wall is generally reached when the diameter of the vessel is 1.5 times greater than normal diameter of 3 cm or less. The term aneurysm applies when the enlargement of the aorta has increased by 50% or more in diameter. Health factors such as blood pressure, age and gender will alter the diameter of the aorta. A true aneurysm of the arterial wall will cause different forms of enlargement or bulges and will also involve all three layers of the arterial wall. With a saccular aneurysm, the tunica media and tunica intima which are the inner most layers of the artery, rupture causing a “blood filled bulge or sac” in the vessels’ outermost wall (Aneurysm, 2002, p.386). A saccular aneurysm, (see Figure 1), bulges from only one side of the aortic vessel and has a distinct neck. The fusiform aneurysm, (see Figure 1), is similar to a saccular aneurysm in that the shape is also a ballooning, but pressure causes all sides of the aortic vessel to bulge outward. The fusiform is the most common form of abdominal aneurysm. A small percentage of aneurysms occur in the thoracic aorta however, the majority occur in the abdominal aorta generally in the area below the renal arteries (Aneurysm, 2002).
Note: Figure 1 Retrieved October 11, 2007, from http://www.daviddarling.info/encyclopedia/A/aneurysm.html
Symptoms of abdominal aneurysms vary from having no pain to onset of steady pain. Typically there is no pain until the aneurysm reaches a size of rupture. A person may have an awareness of a pulsation; however, rupture can occur quickly and usually without any prior symptoms. When the aneurysm is connected to the posterior wall of the aorta, the pain experienced is one of two kinds. The pain is either a fixed, pulsating pain radiating to the back, or there is a sharp, acute pain radiating along the lumbar nerves. The specific pain is a result of location and size of the sac and the pressure it causes on the surrounding area. Conversely, if the aneurysm is located on the anterior surface of the aorta near the celiac axis, the subsequent pain from the pulsating sac will cause symptoms such as constipation, nausea and vomiting, indigestion (dyspepsia) as well as a steady pain in a fixed position near the loins or epigastric region. As previously stated, pain is generally only evident when an aneurysm is reaching point of rupture; most often, aneurysms are asymptomatic (Gray, 1974).
Since there is not just one factor that causes abdominal aneurysms, lab values are useful from an overall general health analysis. Arteriosclerosis/atherosclerosis, male gender, age, cystic medial necrosis, embolism and trauma to the abdomen are some of the risk factors involved with aneurysm. Genetic disposition is still being debated as to the relevancy of risk. Other risk factors may include hypertension, smoking, obesity, and emphysema (Merk, 1999).
An aneurysm is rare before the age of 50 and is more common in men than women. Higher risk groups for the development of aneurysm include those with a family history of abdominal aortic aneurysm (AAA), especially immediate family members. Also, patients with peripheral vascular disease and people with history of popliteal or femoral artery aneurysms are at risk for AAA (Bessen, 2002).
The lab values associated with arteriosclerosis include high blood levels of low density lipoprotein cholesterol (LDL) and low blood levels of high density lipoprotein cholesterol (HDL) which are variable per individual person. Total cholesterol is borderline high with values of 200-239 mg/dl and considered high with levels greater than 239mg/dl. Hypertension lab values present blood pressure above normal with systolic readings of 140-159 mmHg and diastolic reading of 90-99 mmHg over three readings (Merk, 1999). Other pertinent tests that assess complications from hypertension include blood urea nitrogen and serum creatinine to detect renal dysfunction, urinalysis, and complete blood count to name a few (Sommers, Johnson & Beery, 2007).
If an aneurysm is found before symptoms appear, most often it is found as an incidental finding
from other testing procedures. During routine health exams, an aneurysm may be detected if the patient’s abdomen is inspected for pulsating masses in or near the umbilicus. An aneurysm may also present with audible abnormal vascular sounds at the site. Increased pulse and respirations with a decrease in blood pressure may indicate impending rupture of an aneurysm. Any changes in the quality or characteristics of peripheral pulses are also an important finding for the diagnosis of abdominal aneurysm (Sommers, et al, 2007).
Imaging tests that are useful for diagnosis of aneurysms include computed tomography (CT) scan, abdominal x-ray, ultrasound exam, aortography, and magnetic resonance (MRI) imaging. All of these tests are able to assess the location and size of an aneurysm. CT and MRI scans are costly tests with results that can be achieved through other means. The calcifications present in the aorta aneurysm wall may be shown through x-ray, while aortography is a good way to see the extent of an aneurysm but it may err in correct measurements of the aortic dilation as it only outlines the lumen of the vessel (Merk, 1999). Figure 2 below depicts an AAA diagnosed with CT.
Note: Figure 2. CAT scan shows a very large aortic aneurysm (arrow). Retrieved October 20, 2007, from http://www.vascularweb.org/_CONTRIBUTION_PAGES/Patient_Information/3_Most_Common_
Recent clinical trials conducted by Eli Atar with the Rabin Medical Center showed promising results using an experimental method of measuring aneurysms before surgery. The MR angiography test according to Atar (2003) “is performed without ionizing radiation or iodinated contrast material. Using MR angiography with gadolinium (contrast agent), the clinician can visualize the aorta and major branches in multiple 3D projections” (Atar, Belenky, Hadad, Ranany, Baytner, & Bachar, 386). Figure 3 below depicts an AAA diagnosed with MR angiography.
Note: Figure 3. Contrast-enhanced 3D maximum-intensity-projection MR angiographic image shows abdominal aorta and its major branches. Retrieved October 14, 2007, from http://www.ajronline.org/cgi/content/full/186/2/386
One widely available exam for routine screening of an abdominal aneurysm is ultrasound. Ultrasound offers a noninvasive cost-effective technique for imaging and measuring the abdominal vessels. It is virtually 100% reliable in detecting AAA and diameter measurements of the aortic vessel are very accurate. Ultrasound also offers the emergency patient a distinct advantage with speed of testing and the portability of ultrasound machines alleviating the need to move an unstable patient. Ultrasound is useful as well in an emergency situation for providing timely clinical differential diagnosis if an AAA is ruled out. Limitations of ultrasound testing do exist. Ultrasound is operator and machine quality dependent and susceptible to misinterpretation due to health factors such as patient obesity and excessive bowel gas (Bessen, 2002). Figure 4 below depicts an AAA that is diagnosed using ultrasound imaging. The image represents a sagittal as well as a transverse scan plane of the AAA.
Note: Figure 4. Sag (A) and Trans (B) sonograms of an abdominal aortic aneurysm. Markers denote the outside of the aneurysm wall. The central patent lumen is surrounded by an echogenic mural thrombus. Retrieved October 14, 2007, from Besson, (2002). (Courtesy of Richard Rensio, MD.)
Clinical studies are also validating the use of ultrasound as an effective tool in the measurement of plaque build up in atherosclerosis, a risk factor of aneurysm. There is recent information and recommendations that people at risk for aneurysm such as men over age 55 and women over 70 would benefit from routine screening and measurement of the aortic vessel. Any lumen diameter over 6 cm is highly subject to rupture (Sommers, et al, 2007).
Non surgical treatment of an aneurysm includes regular interval monitoring of vessel diameter, medications to control hypertension and patient adherence to general guidelines of a healthy lifestyle (Sommers, et al, 2007).
There is continuing debate on when to surgically intervene to provide treatment of an aneurysm. Some medical institutions such as Stanford University Hospital prefer to monitor the growth and size of an aneurysm before surgery is implemented. The aneurysm must reach a size greater than 5cm and have a growth rate of 0.5 cm for 6 months - 1 year before surgery is relative. In addition, the general health of the patient is taken into consideration before opting for surgical intervention. This monitoring approach may be the best option if the risk of elective surgery is too high due to serious underlying health problems of the patient (Sommers, et al, 2007).
A study conducted in 1992 reviewed the management of aneurysms in clinical case data from
1966-1992. The study compared monitoring and waiting versus early surgical intervention of aneurysms with a diameter of less than 5cm. Conclusions showed that the majority of cases reviewed preferred surgical intervention instead of monitoring the growth of the aneurysm. Waiting was only preferred if the patient was thought to have a low risk of AAA rupture and if the diameter of the aneurysm was less than 4cm (Katz, Littenberg & Cronenwett, 1992).
Another study of aneurysms meant to clarify whether the diameter played a crucial role in the success of surgical treatment (before rupture) after 5 years. The results showed that patients with aneurysm diameter of less than 5 cm have the best outcome at the 5 year post surgery mark with survival at 99%. However, patients with larger AAAs still have a favorable survival rate at the 5 year post surgery mark of 92% while medium size AAAs (5-6 cm) are very favorable for survival at 97% (Zarins, Crabtree, Bloch, Arko, Ouriel &White, 2006).
There is no debate however as to treatment of an aneurysm that is leaking; immediate surgical intervention is necessary. Also, in most instances, the treatment for an aneurysm that is 6cm or greater is surgical intervention. The most widely used surgical repair is with the insertion of a synthetic graft that is placed in the aorta. This procedure requires laparotomy, a major abdominal incision, and involves opening an aneurysm longitudinally and repairing from within the vessel. During repair, it is necessary to clamp the aorta above and below the aneurysm to stop blood flow while the aneurysm sac is opened and the debris of blood is cleaned out of the vessel. A synthetic graft is then placed in the arterial wall while the aneurysm wall is brought together and sutured closed around the graft. If the aneurysm involves the aortic bifurcation then a bifurcated graft is used. The patient is placed on an anticoagulant to reduce the chance of clotting in the lower extremities (Sommers, et al, 2007). The diagram in figure 5 represents the surgical steps necessary to repair an AAA using laparotomy.
Note: Figure 5. Retrieved October 21, 2007, from MD Consult database (From Kent KC, et al. Surgical principles for operative treatment of aortic aneurysms. In Lindsay J Jr [ed]: Diseases of the Aorta, Philadelphia, Lea & Febiger, 1994, p 287.)
Another less invasive method of repairing aneurysms that have not ruptured involves insertion of a stent graph into the femoral artery through a small incision in the patients’ groin (see Figure 6). The compressed stent is guided to the proper position via a catheter with x-ray guidance. Once in place, the stent graph decompresses providing reinforcement of the aorta at the aneurysm site. This procedure called, Endovascular Repair (EVAR), creates less risk for patients already considered high risk surgical candidates. Periodic follow up is necessary with this surgery as the stent grafts have the potential to leak over time which could add to further enlargement of the aneurysm (Bessen, 2002).
Note: Figure 6. Retrieved October 14, 2007, from http://www.daviddarling.info/encyclopedia/A/aneurysm.html
Surgical repair of an abdominal aneurysm carries great risk with intensive recovery time for many patients. If the aneurysm ruptures in the retroperitoneal space, posterior aorta, the
surrounding body structures will prevent immediate death by hemorrhage. However, if the aneurysm ruptures in the anterior space it is usually fatal due to the rapid loss of blood with ensuing loss of body functions (Sommers, et al, 2007). The mortality rate of a ruptured aneurysm is approximately 80%. The mortality rate is less than 5% for those patients that decide to have elective surgery to repair an abdominal aneurysm between 5-6 cm. If an aneurysm has a non-fatal rupture, surgery is immediately necessary and the patient acquires a 50% likelihood of having renal failure post surgery. These prognosis statistics indicate the importance of considering the addition of routine tests to detect abnormalities of the aortic vessel (Merk, 1999).
Aortic aneurysms of the saccular and fusiform type are silent killers that are often found incidentally with other tests. Although there are no absolute reasons for acquiring an aneurysm, there are many risk factors involved in their development such as age, gender, smoking and health diseases such as atherosclerosis and hypertension. Fortunately, along with general health screenings, there are several methods of testing available for detection and monitoring of aneurysms. CT scans, MRI scans, and x-ray technology has been available many years, while ultrasound technology is moving to the forefront of cost effective, non-invasive testing options for the patient. The prognosis for survival of a ruptured aneurysm is still relatively low especially if located on the anterior region of the aorta. Thus, it is especially important to educate clinicians as
well as patients to the effectiveness of aortic screenings. At the current time, open surgical repair
or less invasive techniques such as EVAR, is the treatment of choice for aneurysms.
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