Difference Between Aneurysm and Hemorrhage        

Although Aneurysm and Hemorrhage are two blood-related medical conditions, there exists a distinct difference between them. The key difference between these two conditions is that an aneurysm is an anatomical abnormality  where localized dilation occurs in the wall of a blood vessel while hemorrhage is a pathological condition where blood escapes from the circulatory system. However, rupture of an aneurysm can end up with a massive hemorrhage.

What is aneurysm?

An aneurysm is a localized dilatation in the wall of a blood vessel. It will look like a blood-filled balloon attached to the blood vessel. Aneurysms can occur in any blood vessel of the body. Some examples for aneurisms are aneurysms of the circle of Willis, which is located in the base of the brain, and aortic aneurysms affecting the thoracic or abdominal aorta. Sometimes, aneurysms can also occur in the ventricles of the heart itself. This usually occurs due to the weakening of the ventricular wall by ischemic damage.

Aneurisms tend to increase in size with time. This may be accompanied by the weakening or thinning out of its wall. Therefore, aneurysms have an increased risk of rupture.  A ruptured aneurysm can lead to a fatal hemorrhage causing severe hypovolemic shock and death. Aneurysms occur due to hereditary weakness of the blood vessel wall or acquired weakness of the vessel wall by various causes such as degeneration, atherosclerosis, and infections. Aneurysms can also be a site for clot formation (thrombosis) and embolization (dislodge of the clot causing obstruction of blood flow in the distal organs. There are two types of aneurysms.

  • A true aneurysm: Wall of the aneurysm is made up of the arterial wall itself.
  • A false aneurysm (pseudoaneurysm): is a condition where blood is leaking out of an artery and walled off next to the artery by surrounding tissues.

Radiological techniques such as ultrasonic scanning, contrast-enhanced CT scanning, etc. are used to diagnose aneurysms.  Selected growing aneurysms are treated by surgery. Currently, there are various interventional radiologic techniques where a catheter is passed through an artery up to the location of the aneurysm and various procedures (clipping, coiling) are implemented to obstruct the cavity of the aneurism. These technics are especially useful for surgically inaccessible sites such as the base of the brain.

What is Hemorrhage?

Bleeding or hemorrhaging is defined as blood escaping from the circulatory system. The extent of the bleeding can range from a small capillary level bleed to a major life threatening bleed. Bleeding can occur internally in the body, where blood leaks from a blood vessel inside the body, or externally, through a natural opening (e.g. mouth, urethra) or through an injury in the skin. A healthy person can tolerate a loss of 10–15% of the total blood volume without serious consequences. The stopping of bleeding is called hemostasis.

Blood loss can be categorized as below.

  • Class I Hemorrhage: up to a loss of 15% of the blood volume. There will be no change in vital signs.
  • Class II Hemorrhage: up to a loss of 15-30% of the total blood volume. A patient will have a rapid heartbeat with a narrow pulse pressure (narrowing of the difference between systolic and diastolic blood pressures).
  • Class III Hemorrhage: up to a loss of 30-40% of the blood volume. The patient’s blood pressure will drop and the heart rate will increase
  • Class IV Hemorrhage: up to a loss of >40% of the blood volume. The body will not be able to compensate for the blood loss and immediate resuscitation is recommended.

    Subconjunctival hemorrhage eye

What is the difference between Aneurysm and Hemorrhage?

Definition of Aneurysm and Hemorrhage

Hemorrhage: Bleeding or hemorrhaging is defined as blood escaping from the circulatory system.

Aneurysm: An aneurysm can be defined as a localized dilatation in the wall of a blood vessel.

Characteristics of Aneurysm and Hemorrhage

Pathophysiological basis

Aneurysm: Aneurysm is an anatomical abnormality.

Hemorrhage: Hemorrhage is a pathological condition.


Aneurysm: Aneurysm is slowly progressive.

Hemorrhage: Hemorrhage is rapidly progressive.


Aneurysm: Aneurysm commonly causes thromboembolism.

Hemorrhage: Hemorrhage causes hypovolemic shock.

Body Response

Aneurysm: Body does not have a system to prevent the formation of aneurysms.

Hemorrhage: Body has the clotting pathway to control bleeding by sealing the defect in the vessel.


Aneurysm: Aneurysm can be observed without treatment if small.

Hemorrhage: Hemorrhage should almost always be controlled.


Image Courtesy:

“Cerebral aneurysm NIH” by en:National Institutes of Health  (Public Domain) via Wikimedia Commons 

“Subconjunctival hemorrhage eye” by Daniel Flather – Own work. (CC BY-SA 3.0) via Wikimedia Commons