Definition of Aortic Aneurysm
An aortic aneurysm is referred to a condition of bulging growth of more than one and half of the aorta’s width involving the three layers of the vessel wall including the intima, media, and adventitia. Abdominal aortic aneurysms are more prevalent than thoracic aortic aneurysms. Although the normal aortic diameter varies with various factors such as age and gender, average diameters have been determined.
The aneurysm has two main morphologies:
- Fusiform: A type of aneurysm marked by circumferential dilatation of a part of the aortic wall.
- Saccular: A type of aneurysm marked by a localized outpouching of an aortic wall.
Pathophysiology of Aortic Aneurysm
Pathophysiology of aneurysms is multifactorial and complex in nature; however, disruption of elastic fibres of the aortic wall extracellular matrix is the main feature of abdominal aortic aneurysm.
Thoracic aortic aneurysm
Aneurysms of ascending thoracic aorta occur usually due to cystic medial degeneration of the aortic wall, eventually resulting in the weakening of the aorta. Cystic medial degeneration usually occurs due to the following risk factors:
- Hyaline arteriosclerosis caused by uncontrolled aorta.
- Hereditary connective-tissue disorders like Marfan syndrome (an autosomal-dominant disorder developed from the mutation in one of the genes of fibrillin-1).
- Ehlers-Danlos syndrome.
- A family history of thoracic aortic aneurysm syndrome.
Abdominal aortic aneurysm (AAA)
It is multifactorial and associated with alterations in the biology of the arterial wall resulting in the loss of wall strength due to various risk factors contributing in the development of AAA. Please see next for the risk factors.
Risk factors of Aortic Aneurysm
Thoracic aortic aneurysms are caused mainly due to injury, high blood pressure, inherited tissue disorders like Ehlers-Danlos syndrome or Marfan syndrome.
Various risk factors associated with aortic aneurysm, AAA, are the following:
- There is an increased risk of AAA with aging, especially in elderly men above 65 years.
- The incidence of AAA is twice in Caucasian populations than black people.
- Smoking is one of the most common risk factors of AAA as it is associated with atherosclerotic changes of the vessel’s wall preventing the normal nutrients from diffusion into its wall, therefore weakening the vessel wall with subsequent dilatation. Once an aneurysm is formed, continuous active smoking will cause progressive dilatation, expansion and risk of rupture.
- The risk of AAA is high in families with a history of AAA due to genetic predisposition.
- Patients having other large vessels aneurysms (eg, iliac, femoral, popliteal, carotid) are at risk of having AAA due to the same common pathological mechanisms.
- Aortic wall infection can result in the degeneration of a localized area of the aortic wall due to contiguous spreading from a nearby infection or due to septic emboli from associated infective endocarditis.
Clinical manifestations of Aortic Aneurysm
Thoracic aortic aneurysm
Most patients with thoracic aortic aneurysms are asymptomatic at the time of presentation, and they might be discovered accidentally by a chest X-ray showing widened mediastinum, CT scan for other purpose or echocardiography showing dilatation of the ascending aortic aneurysm with possible aortic regurgitation.
Symptoms of thoracic aortic aneurysms arise mainly from the compression of adjacent thoracic structures or vascular sequences.
Compression of adjacent thoracic structures:
- Left recurrent laryngeal nerve compression, hoarseness of the voice.
- Phrenic nerve compression, hemidiaphragmatic paralysis.
- Compression of tracheobronchial tree, cough, wheeze, dyspnea, hemoptysis.
- Esophageal compression dysphagia.
- Superior vena cava compression, superior vena cava syndrome.
1. Aortic regurgitation
AR may occur as a consequence of aortic root dilatation with subsequent distortion of the annulus. This may lead to heart failure and other manifestations, such as dyspnea, orthopnea and paroxysmal nocturnal dyspnea due to pulmonary venous congestion, especially if it is associated with hypertension as a result of overload.
2. Thromboembolic events
Blood stagnation within the aneurysm may result in the development of thrombus, with subsequent embolization into different body organs eventually leading to thromboembolic manifestations.
The most serious presentation of the thoracic aortic aneurysm is aortic dissection that ruptures into the intrapleural space or intrapericardial space. After rupture or dissection of thoracic aortic aneurysms, individuals may feel a sudden, sharp and severe pain in the upper back and abdomen. Eventually, the individuals may go into a state of hypotension and shock (mostly hypovolemic shock).
Abdominal aortic aneurysm (AAA)
Most individuals of AAA show no symptoms, and it is only discovered with routine screening, physical examination or diagnostic imaging modalities for evaluation of other purposes. Although AAA is often asymptomatic, it may result in some characteristic clinical features, such as:
- Pulsatile abdominal mass that is detected accidentally on a routine physical examination.
- Abdominal pain that maybe attributed to another abdominal cause, and therefore a wide variety of differential diagnosis should be considered.
Differential Diagnosis of AAA
Intermittent pain and discomfort in the abdomen that lasts up to 2 – 4 days, along with symptoms of abnormal defecation and bloating can be associated with irritable bowel syndrome. However, crampy abdominal pain with bloody or non-bloody diarrhoea can be associated with inflammatory bowel disease. Pain in the periumbilical position along with nausea, anorexia and emesis can be associated with appendicitis.
Abdominal examination, CT scans, ultrasound examination and angiography can help in the accurate diagnosis of the condition.
The rupture of an abdominal aortic aneurysm can result in the following symptoms:
- Sudden severe pain in the back and lower abdomen
- Urinary problems
- Increased heart rate while standing and sweaty skin.
The ruptured abdominal aortic aneurysm may result in internal bleeding subsequently leading to shock which can be fatal if not treated immediately.
AAA can also be present with thromboembolic events due to embolization of thrombus into various organs with the following symptoms:
- Acute LL ischemia,
- Mesenteric vascular occlusion (MVO) or
AAA may present also with constitutional symptoms as a result of presence of:
- Infected or inflammatory aneurysm.
- Disseminated intravascular coagulation (DIC).
Symptoms of fever, malaise, chronic abdominal pain and weight loss may suggest underlying inflammatory aneurysm, which affects about 5 – 10% of patients with AAA.
Extensive large AAA may present with DIC manifestations resulting in either thromboembolic or hemorrhagic manifestations.
Other less common presentations of AAA:
- Acute myocardial infarction as a result of a massive loss of blood.
- Heart failure as a result of AV fistula between the aorta and inferior vena cava.
- Upper GIT bleeding may occur as a result of ortoduodenal fistula.
Diagnosis and clinical investigations of Aortic Aneurysm
Patient history with chest or back pain, constipation, and abdominal distension should be considered for further tests and examination. Aortic aneurysm should be in the differential diagnosis in the presence of the previously described clinical manifestations.
Thoracic aortic aneurysm should be suspected in the presence of an aortic regurgitation murmur or sudden onset of heart failure signs and symptoms.
Abdominal aortic aneurysm should be suspected in the presence of unusual, strong pulsatile upper abdominal mass.
ESR tests and blood cultures
ESR tests and blood cultures demonstrate elevated ESR and positive blood cultures which occur in inflammatory aortic aneurysms.
Plain chest X-ray examination from check-ups can detect aneurysms and appear as a protruding shadow from the ascending aorta. Thoracic aortic aneurysms are diagnosed from a chest X-ray and characterised by tracheal deviation or enlargement of aortic knob, while smaller aneurysms are not detected by chest X-rays.
Abdominal ultrasound is considered for the detection of abdominal aortic aneurysm. It is the standard method for monitoring and screening of abdominal aorta aneurysms.
Aortic dilation of greater than 1.5 is associated with aneurysm.
Men 60 years or older with a family history of AAA in parents should undergo abdominal U/S evaluation of possible underlying AAA. Men who are 65 – 75 years old and have a history of current or previous smoking should undergo assessment for AAA.
Transthoracic echocardiography is an effective diagnostic tool for aortic root imaging and is usually used for the evaluation of patients with Marfan syndrome.
The method is semi-invasive in nature and therefore not a preferred method for imaging as it may miss the diagnosis.
MR angiography and Contrast-enhanced CT scanning
MR angiography and Contrast-enhanced CT scanning are preferred for detecting the size and presence of thoracic aortic aneurysms.
MR angiography is an alternative where images are in multiple planes and therefore allows on-axis measurements.
Contrast-enhanced CT is used for generating a 3D image of the aorta which demonstrates a combination of spatial resolution, reproducibility and speed for detection of AAA.
Tissue Doppler Imaging (TDI)
Another ultra-sonographic technique referred to as Tissue Doppler Imaging (TDI) allows the measurement of wall motion along the arterial segment.
AAA commonly leads to changes in aortic wall properties and therefore can be detected using these techniques.
Treatment of Aortic Aneurysm
Aortic aneurysms can either be treated medically or surgically based on the size and location of the aneurysm, the maximal diameter and the associated conditions such as Marfan syndrome. However, it is important to prevent growing, rupture or dissection of the aneurysm by controlling the risk factors and enhancing the quality of life.
It is generally accepted that the diameter of abdominal aortic aneurysm is the best predictor for the risk of rupture.
It is very clear that the risk of rupture increases when the aneurysm increases from 5 cm to 6 cm in size.
The patients treated for aneurysm should be advised on the effective management of blood pressure. Routine daily activities should be continued with minimal restrictions along with minimal exercise.
Lifestyle modification of the patients should be considered. Patients and their family should be educated on the risks associated with aortic rupture or dissection and its symptoms. Stress on the aorta plays a big role in acute aorta rupture or dissection; thus, patients should be restricted on heavy weight lifting or competitive athletics.
Patients should be advised to appear for regular follow-up imaging tests like MRI or CT for effective long-term management, as continuous monitoring of the size of the aneurysm is important for further treatment and management.
Diagnostic imaging must be repeated and compared to the initial images at:
- 6 – 12 months for aneurysms 4.0 to 5.4 cm in diameter
- 2 – 3 years for aneurysms 3.0 to 4.0 cm
- Every 5 years for aneurysms 2.6 to 2.9 cm
Yearly interval monitoring with images is accepted when there is no growth of the aneurysm.
A follow up at 3 – 6 months should be done if there is a significant increase in the size of the aneurysm in comparison to the previous size.
Patients should be recommended to attend rehabilitation programs for cardiovascular diseases which are designed for acute phases during hospitalisation, early stage after discharge and 1 – 2 months after onset and for patients with more than 2 months after the onset of an aneurysm.
Asymptomatic thoracic aortic aneurysm
Asymptomatic thoracic aortic aneurysms are initially treated medically with aggressive control of two main factors:
- Blood pressure
- Heart rate
The main aim is to slow the progression and the expansion of the aortic aneurysm size, thereby lowering the risk of rupture or dissection of the aneurysm.
Beta-blockers, such as Propranolol, are considered very effective in controlling the blood pressure and heart rate, especially in patients with Marfan syndrome, by the following mechanisms:
- Reducing the rate of aortic dilatation.
- Decreasing the shearing stress.
- Decreasing the left ventricular contractility.
Asymptomatic abdominal aortic aneurysm (AAA)
Conservative treatment is recommended in asymptomatic infra-renal abdominal aortic aneurysm <5.5 cm rather than surgical repair as the risk of aneurismal rupture becomes high when the diameter exceeds the 5.5 cm.
It is appropriate, for patients with AAA, to receive Statins and Aspirin to decrease the risk of cardiovascular events, as it is considered coronary equivalent.
Surgery is recommended in cases where the aneurysm is rapidly increasing in size. Two types of surgery are known for repairing the aortic aneurysms which include:
- Open chest or abdominal repair, and
- The endovascular repair.
The open chest repair or open abdominal surgery is the standard type of surgery for the treatment of aortic aneurysms. The surgery involves a procedure of making a major incision in the chest or the abdomen. The surgery requires the use of general anaesthesia while the aneurysm is removed from the affected area. The aorta section is replaced by a graft made from Teflon or Dacron.
Thoracic aortic aneurysm (AAA)
Prophylactic surgical repair of the thoracic aortic aneurysm is recommended to prevent the mortality of aneurysm rupture.
The indications of surgical repair are:
- Symptomatic thoracic aortic aneurysms.
- Rapid growth rate (≥10 mm / year) in aneurysms <5 cm in diameter.
- Evidence of dissection.
- Ascending thoracic aortic aneurysm >4.5 cm at the same time of aortic valve surgery.
- Aortic diameter of 5 – 6 cm for ascending aortic aneurysm.
- Aortic diameter 6 – 7 cm for descending aortic aneurysm.
- Aortic diameter ≥7 cm in high-risk patients.
Abdominal aortic aneurysm (AAA)
Elective repair of the AAA is considered the best method of prevention of aortic rupture, either by open surgery or endovascular surgery.
The indications of elective AAA repair include good risk surgical candidates with:
- AAA >5.5 cm
- Rapidly expanding AAA
- AAA associated with peripheral arterial aneurysm, or peripheral artery disease
Endovascular Aneurysm Repair (EVAR)
The procedure of endovascular aneurysm repair emerged in the 1990s as an alternate method for the treatment of aneurysm; however, this quickly gained an important role in the clinical management of aortic aneurysm. Various studies have shown equivalent efficacy and safety of EVAR when compared to the conventional method of open surgical repair.
This method also demonstrates various short-term benefits which include:
- Reduction of blood loss,
- Minimum hospital stays,
- Rapid recovery and
- Minimal complications due to its less invasive nature.
Endovascular repair of aneurysm does not involve the removal of the aneurysm. In this procedure, the aorta is strengthened by inserting a graft. Catheters are inserted into the arteries and the graft is placed at the affected aorta. This procedure does not involve opening of the abdomen or the chest.
The procedure uses general anaesthesia. A catheter is inserted into the groin and threads the graft to the aorta affected by the aneurysm. The complete procedure is performed using X-ray of the artery.
The graft is expanded after the insertion in the aorta and fastened to it. This ensures a stable flow of blood and prevents rupturing of the aneurysm.