What is Abdominal Aortic Aneurysm?
Abdominal aortic aneurysm is a localized ballooning or dilatation of abdominal aorta that exceeds standard diameter length by more than 50%. It is the most prevalent type of aortic aneurysm. Nearly 90% of all abdominal aortic aneurysms develop below the kidneys; these are known as juxtarenal or infrarenal abdominal aortic aneurysms. However, they can also develop pararenally or at the kidney level or suprarenally (above kidney level). Aneurysms like these can also include either both or at least one of iliac arteries present in the pelvis.
Abdominal Aortic Aneurysm ICD-9 Code
The ICD-9 Code for this condition is 441.3 and 441.4.
Abdominal Aortic Aneurysm Prevalence
The condition mostly affects men who are above 60 years of age. It is more frequent in case of smokers than in nonsmokers. Women are rarely affected by this disorder.
Abdominal Aortic Aneurysm Classification
These aneurysms are generally divided based on their symptoms and size. The normal diameter of an aorta is close to 2 centimeters. An aneurysm is said to have developed when the outer aortic diameter exceeds over 3 centimeters. When the outer diameter becomes more than 5.5 centimeters, physicians consider the aneurysm to be large.
Abdominal Aortic Aneurysm Causes
The exact factors as to what causes this degenerative process remains unknown. However, some probable risk factors that may cause this condition have been identified.
Gene
Certain genetic factors are believed to be responsible for this aortic condition. The high rate of familial prevalence is most prominent in the male individuals. Several hypotheses exist as to which exact genetic defect is responsible for the high incidence of abdominal aortic aneurysm among the male members of affected families. Deficiency of alpha 1-antitrypsin is believed to be a crucial factor by some physicians, whereas some other healthcare professionals are of the opinion that X-linked mutation responsible for low incidence in the heterozygous females should be held as the main cause. Connective tissue disorders like Ehlers-Danlos syndrome and Marfan syndrome are also supposed to strongly related to AAA. Pseudoxanthoma elasticum and relapsing polychondritis may also result in AAA.
Smoking
More than 90% of individuals with this condition have smoked at one point or another in their lifetime.
Atherosclerosis
For a long time, Atherosclerosis was believed to be responsible for the causation of aortic abdominal aneurysm as the walls of AAA are often affected heavily. However, this hypothesis could not be used for explaining the development of occlusion or the initial defect that is seen in the process.
Other factors
The other conditions that might lead to the development of these aneurysms include:
- Trauma
- Obesity
- Arteritis
- Atheroma
- Emphysema
- Genetic factors
- High cholesterol
- High blood pressure
- Cystic medial necrosis
- Vasculitis or aortic infection
- Aging, as it occurs mostly in people above 60 years of age
Abdominal Aortic Aneurysm Pathophysiology
The most notable histopathological changes of the aneurysmatic aorta are visible in the tunica media and tunica intima. These changes include:
- Buildup of lipids in foam cells
- Thrombosis
- Calcifications
- Cholesterol crystals
- Ruptures and ulcerations of the layers
An adventitial inflammatory infiltration can be seen. However, it seems that degradation of the tunica media through proteolytic process is the basic pathophysiologic procedure behind AAA development. Certain researchers report an increased activity and expression of matrix metalloproteinases in AAA patients. This leads to elastin elimination from the media, making the aortic wall vulnerable to influence of blood pressure. The quantity of vasa vasorum is also reduced in abdominal aorta. Naturally, the tunica media has to depend mainly on diffusion for nutritional needs which make it more vulnerable to damage.
Hemodynamics influences the development of aortic abdominal aneurysm, and has got a predilection for infrarenal aorta. The mechanical characteristics and histological structure of infrarenal aorta differs from those of thoracic aorta. Diameter is reduced from root to bifurcation, and abdominal aortic wall contains lesser amount of elastin. Hence there are higher mechanical tensions in the abdominal aortic wall than in thoracic aortic wall. With age, the elasticity and distensibility of the abdominal aortic wall declines. This might result in the gradual dilatation of this segment. In patients having arterial hypertension, higher intraluminal pressure strongly contributes to progression of pathological process. Certain specific patterns of Intraluminal Thrombus (ILT) along aortic lumen may be connected to suitable hemodynamics conditions. This, in turn, may influence the development of AAA.
Abdominal Aortic Aneurysm Symptoms
The aorta is the main blood vessel supplying blood to the human body. It runs from the heart through center of one’s chest and abdomen. Bursting or rupturing of an abdominal aortic aneurysm is a life-threatening situation presented by this condition which can cause incessant bleeding. The majority of the aneurysm cases are asymptomatic although in some cases they may cause abdominal, leg or back pain.
Painful sensations may be experienced if there is expansion of these abdominal aortic aneurysms, along with pulsating sensations in abdomen with pain in the lower back, chest, or scrotum. In symptomatic aneurysms, there is a considerably higher risk of rupture and surgical operation is required to remedy the situation. Symptoms of abdominal aortic aneurysm might also include small blood clots known as emboli that are sometimes formed on the inner lining of AAA. These blood clots may eventually lead to pain, stroke or tissue death. A blatant abdominal mass might be observed on physical examination. Presence of bruits in case of visceral or renal arterial stenosis is a possibility.
The clinical manifestation of a ruptured AAA normally includes agonizing pain in the groin, abdomen, flank and lower back areas. The bleeding normally leads to hypovolemic shock accompanied by an altered mental condition as well as:
- Hypotension
- Cyanosis
- Tachycardia
Other symptoms include:
- Paleness
- Dry mouth and skin
- Nausea
- Vomiting
AAA rupture leads to death in almost 90% of all cases. Bleeding in a rupture or leaking can be either intraperitoneal or retroperitoneal; the rupture can even create an aortointestinal or aortocaval fistula. Retroperitoneal hemorrhage is indicated by a bruise known as Flank ecchymosis; it is also referred to as Grey Turner’s sign.
Abdominal Aortic Aneurysm Diagnosis
Abdominal aortic aneurysms are normally diagnosed by conducting physical exams, ultrasound and CT scans. A plain abdominal radiograph can show the outlines of an aneurysm once its walls have been calcified. However, this happens in less than 50% of all aneurysms. Abdominal aortic aneurysm screening is done by ultrasonography which also helps to unravel the mass of any present. It is also possible to detect free peritoneal fluid. This is sensitive and noninvasive; however its usefulness may be limited by obesity or the existence of bowel gas. CT scans are highly effective diagnostic tools for detecting aneurysms and is useful in pre-operative planning, mapping the anatomy as well as the possibility for an endovascular repair. If a rupture is suspected, a CT scan also reliably detects retroperitoneal fluid. A ruptured AAA shows the triad of signs and symptoms which include shock, pain and a pulsating abdominal mass. No further clinical tests are required before surgery if these three conditions are present.
An X-ray imaging of the abdomen might show deposits of calcium lining an aneurysm’s wall in some cases. Arteriograms are real time x-rays that are conducted for similar purposes. Other diagnostic procedures for visualizing the aneurysm include angiography and MRI, although these methods are not much used.
An aneurysm ruptures or breaks if mechanical stress, expressed as tension per area, surpasses the strength of the local wall. As a result, PWS (peak wall stress) and PWRR (peak wall rupture risk) are considered to be more dependable parameters than diameter for analyzing AAA rupture risk. Computing the rupture risk probabilities from the standard clinical CT figures is made possible by medical software, helping to come up with a patient-specific abdominal aortic aneurysm rupture risk diagnosis.
Abdominal Aortic Aneurysm Differential Diagnosis
Aortic Dissection is a condition that is similar to AAA.
Abdominal Aortic Aneurysm Treatment
Asymptomatic AAA is treated by conservative management, which includes surveillance for eventual repair, and then immediate repair. Two methods of abdominal aortic aneurysm repair currently exist: the open aneurysm repair, also abbreviated as OR and the endovascular aneurysm repair, or EVAR. Intervention is often necessary if an aneurysm grows in size more than a centimeter in a year or it’s bigger than 5.5 centimeters. Repair is indicated for the symptomatic aneurysms as well.
Conservative Treatment
Conservative management is carried out in cases involving risk of a high mortality as well as in cases where repair work is highly unlikely to improve the life expectancy of patients. Cessation of smoking is the mainstay of conservative treatment.
Surveillance is recommended in asymptomatic aneurysms smaller than 5.5 centimeters where risk of repair is greater than risk of rupture. The probability of a rupture increases with an increase in the diameter of an aneurysm. Surveillance, until an aneurysm reaches the diameter of 5.5 centimeters, lowers the risks that might be imminent with early intervention.
Medications
No form of medical therapy has yet been proven to be effective in decreasing the rupture rate or growth rate of asymptomatic aneurysms. Lipids and blood pressure should be treated like that of any atherosclerotic condition. It is suggested that therapy using medications such as beta-blockers, angiotensin-converting enzyme inhibitors and statins might produce possible protective effects.
Surgery
The threshold for surgical repair varies to some extent from one individual to another, and depends on the comparison of the pros and cons between repair and ongoing surveillance. Size of the native aorta of a patient might influence this, together with incidence of comorbidities that increases the operative risk or reduces life expectancy.
Endovascular repair
Although endovascular repair has been prevalently in use since the 1990s as an alternative method of treatment to open repair, the role of this procedure is not clearly defined yet. The procedure involves resection and is mostly carried out in older and high-risk patients or the patients who are unfit for an open repair. However, the method is feasible only for a small proportion of aneurysm cases, determined by the morphology of an aneurysm. Advantages over an open repair procedure include less peri-operative mortality rate, less intensive care duration, less time spent in overall hospitalization and an earlier return to day-to-day activity. Disadvantages of this form of repair include a need for more frequent hospital follow up reviews as well as a greater chance of additional procedures being required. Although this procedure is not a strictly better one compared to the open surgery, instances of aneurysm-related mortality are lower with EVAR. A stent graft is used in this process.
Open repair
This procedure is mostly carried out as an elective method in young patients for growing, large symptomatic or even ruptured abdominal aortic aneurysms.
Keyhole Surgery
This procedure involves making 2 or 3 small cuts in the patient’s abdomen and inserting a telescopic camera for inspecting the aneurysms. A graft is then placed strategically through other cuts for treating the aneurysms.
Abdominal Aortic Aneurysm Complications
Complications following an endovascular repair of aneurysm include endotension, a condition in which the aneurysm sac might remain under pressure. Other complications of the condition include:
- Rupture
- Acute aortic occlusion
- Peripheral embolization
- Aortocaval or aortoduodenal fistulae
Abdominal Aortic Aneurysm Prognosis
The outcome of the treatment of AAA is generally good if the aneurysm is repaired by an experienced surgeon before rupturing. Once such an aneurysm begins to rupture or tear, it becomes a medical emergency. The survival rate in such cases is less than 80%.
Abdominal Aortic Aneurysm Prevention
AAA can be prevented by following certain measures, such as:
- Giving up smoking
- Switching to a low-fat diet
- Undergoing treatment for hypertension
- Mortality has been known to be reduced by screening of abdominal ultrasounds for men above 65 years of age
Abdominal Aortic Aneurysm Pictures
Here are some images that demonstrate the location as well as the mechanism by which these aneurysms are formed.
Picture 1 – Abdominal aortic aneurysm
Picture 2 – Abdominal aortic aneurysm Image
Abdominal aortic aneurysm is an almost fatal condition affecting the abdominal aorta. The condition, when accompanied by rupturing, is considered to be a medical emergency. AAA should not be left untreated and immediate medical attention is required to ensure close inspection of the patient’s condition. At present, further research is being conducted in the area of rupture-risk assessment to yield better results of treatment in the future.