What is Aneurysm or Aneurism?
Aneurysm is a localized swelling or bulge in the vessel wall. It is an abnormal dilatation in the blood vessel. This is due to weakening of the vessel wall. As the blood passes through the weakened portion of the vessel, it dilates or bulges and if this continues, it can rupture, which can be very fatal leading to internal bleeding, organ damage and even death.
Aneurysms are more common in arteries than veins. Arteries are those blood vessels which carry oxygen rich blood to different parts of the body. The walls of the arteries are thick enough to withstand the pressure of the blood, but sometimes congenital conditions, trauma or other medical problems can lead to weakening of the vessel wall and the continuous flow of the blood through that weakened portion results in the formation of aneurysm. If this continues, the aneurysm gets larger, which can result in either rupture or dissection of the aneurysm. Rupture causes internal bleeding.
Dissection is a split in one or more layers of the artery walls where blood can seep within the layers of the wall. Both rupture and dissections are fatal.
Classification and Types of Aneurysm or Aneurism
The classification of aneurysm depends on its type, location and affected vessel.
True and False Aneurysm or Aneurism:
- A true aneurysm involves all the three layers of the artery wall, i.e. tunica intima, tunica media and tunica adventitia. Atherosclerotic, syphilitic, congenital aneurysms and ventricular aneurysms come under true aneurysms.
- A false aneurysm or pseudo-aneurysm does not involve distortion of all the layers of the vessel wall. In pseudo-aneurysm, the blood leaks through a hole or a puncture in the arterial wall and forms a hematoma outside the vessel. It is confined by the surrounding tissues and is connected to the actual vessel. Generally pseudo-aneurysms are caused by trauma or injury that punctures the artery e.g. percutaneousarterial procedures such as arteriography, arterial grafting, or use of an artery for injection, such as by drug abusers. The walls of pseudo-aneurysm are not formed by the arterial layers, but by the hematoma.
Classification Based On Morphology:
- Aneurysms are classified according to their shape and size such as saccular aneurysm and fusiform aneurysm.
- Saccular aneurysm is spherical in shape where only a portion of the circumference of the vessel wall is involved. The most common cause of saccular aneurysm is syphilis. In fusiform aneurysm, the entire circumference of the vessel wall is involved. They are spindle shaped. The most common cause is arteriosclerosis.
Classification Based On Location:
- Cerebral aneurysms (intracranial or brain aneurysms), occur most commonly in the anterior cerebral artery. The next most common site of cerebral aneurysm occurrence is in the internal carotid artery.
- Most of the non-intracranial aneurysms arise distal to the origin of the renal arteries at the infrarenal abdominal aorta, a condition thought to be related to atherosclerosis. Abdominal aortic aneurysms are considered to be a separate pathology. In some cases the thoracic aorta is also involved. A common form of thoracic aortic aneurysm involves dilatation of the proximal aorta and the aortic root leading to aortic insufficiency. Aneurysms can also occur in the legs, especially in the deep vessels e.g. the popliteal vessels in the knee.
- Arterial aneurysm is more common than venous aneurysm, but venous aneurysms do occur e.g. popliteal venous aneurysm.
Pathophysiology Of Aneurysm or Aneurism
The occurrence and expansion of an aneurysm depends on the local hemodynamic factors and factors intrinsic to the arterial segment itself.
The aorta has a relatively low-resistance circuit for circulating blood and the lower extremities have higher arterial resistance. Repeated trauma of a reflected arterial wave on the distal aorta may injure an already weakened aortic wall and lead to aneurysmal degeneration. Systemic hypertension further increases the injury, accelerates the expansion of existing aneurysms, and also contributes to their formation.
Aneurysm formation is due to multiple factors affecting the arterial segment and its local environment. Many aneurysms are atherosclerotic in nature. As the aneurysmal dilatation increases, the arterial wall tension also increases and this can result in rupture of the aneurysm. Increase in blood pressure (systemic hypertension) leads to increase in aneurysm size, which in turn increases the arterial wall tension and therefore increases the risk of rupture.
The vessel wall is supplied by the blood within its lumen although the aorta has vasa vasorum, therefore as the aneurysm develops, the mostischemic portion of the aneurysm is at the distal end, which results in weakening of the vessel wall there and aids in further expansion of the aneurysm. Thus eventually, all aneurysms if left to their natural course rupture without intervention.
Aneurysms that result from an infectious process involving the arterial wall are called mycotic aneurysms. The term “mycotic” is misleading implying a fungal cause. In fact, the main pathogens of mycotic aneurysms are gram-positive cocci, e.g. bacterial endocarditis can cause mycotic aneurysm by blocking the small arteries with infected emboli.
While most aneurysms occur in an isolated form, the occurrence of berry aneurysms is always confined to the base of the brain. Berry aneurysms are the smallest aneurysmal dilatations and are congenital in nature.
Syphilis is the most common cause for inflammatory aneurysm, involving aorta and resulting in saccular aneurysm.
Epidemiology Of Aneurysm or Aneurism
Cranial aneurysms incidence rates are estimated at between 0.4% and 3.6%. Those who don’t have risk factors have expected prevalence of 2 to 3%. When compared to males, females are more likely to have aneurysms, especially those who are between 60 and 80. Aneurysms, though rare in children, have different incidences and features than adult aneurysms. More than 95% of aneurysms occur in adults. The mortality rate for pediatric aneurysm is lower when compared to adults. Intracranial hemorrhages are twice more likely to be due to aneurysms than cerebral arteriovenous malformations in whites and are four times less in certain Asian populations.
Causes And Risk Factors Of Aneurysm or Aneurism
- Tobacco Use
- High Cholesterol
- Copper Deficiency
- Increasing Age
- Congential or inherited weakness in artery walls
- Pregnan (cysplenic artery aneurysm)
Signs And Symptoms Of Aneurysm or Aneurism
The symptoms depend on the location of the aneurysm. If the aneurysm is present close to the body’s surface, then pain and swelling with a throbbing mass is seen. Aneurysms which are present within the body or brain usually don’t cause symptoms.
If an aneurysm ruptures, then pain, low blood pressure, rapid heart rate, and lightheadedness may occur. The risk of death after a rupture is very high. can appear in different places, specifically in the aorta, neck, brain, head and in abdomen. Symptoms need not be necessarily obvious; however, the following symptoms could be used as indicators:
- Expansile pulsation.
- Dullness to percussion.
- Systolic murmur.
- Loss of perception.
- Loss of balance.
- Speech problems.
- Double vision.
- Severe headaches.
- Loss of vision.
- Neck pain and/or stiffness.
- Pain above and/or behind the eyes.
Pressure Symptoms Such As:
- Brassy cough.
- Laryngeal paralysis.
- Tracheal tugging.
- Unequal pupils.
Treatment for Aneurysm or Aneurism
Surgery is the choice of treatment. The type of surgery done and its requirement depends on the symptoms of the patient and the size and type of the aneurysm.
For intracranial or brain aneurysms, surgical clipping, or endovascular coiling is done.
For aortic and peripheral aneurysms (aneurysms in the aorta, arms, legs, or head), bypass grafting of the weakened section of the vessel is done and is sutured at the vascular stumps.
Prognosis Of Aneurysm or Aneurism
With successful surgical intervention, the prognosis is often excellent, but in patients with ruptured aneurysm, the prognosis depends on the age and general health of the patient, pre-existing neurological conditions, location of the aneurysm, extent of bleeding, and time elapsed between the rupture and treatment. Statistics reveal that about 40% of individuals with ruptured aneurysm do not survive the first 24 hours and 25% of them result in death from complications within 6 months. Patients with subarachnoid hemorrhage may have permanent neurological damage; however, other individuals may recover with little or no neurological deficit. There can be delayed complications from a burst aneurysm such as hydrocephalus and vasospasm. Early detection of aneurysm and treatment is important.
Tests to Diagnose Aneurysm or Aneurism
- CT Scan.
- Ultra Sound.
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