
Health x Wellness
Understanding Aneurysms: Causes, Risks, and Treatments
An aneurysm is an abnormally weakened area in an artery causing it to bulge outwards. It can cause problems such as bleeding, exsanguination/death, stroke, and limb loss, hence vascular specialists pay particular attention to these uncommon but dangerous vascular conditions.
There are two types of blood vessels: arteries and veins, where arteries are the pipe-system that delivers life-giving blood to all parts of our body, while veins return the ‘spent’ blood back to the heart evacuating with it waste products from the tissues.

Arteries contain blood pressure that the heart generates from its beating motion to propel the blood forwards, while vein or venous blood have no or very-low blood pressure. Aneurysms affect mostly arteries and because arteries contain blood pressure, this combination makes arterial aneurysms particularly deadly.
An overview of the arterial system (or arterial tree) is as follows
- The heart pumps oxygen- and nutrient-rich blood into the biggest artery in the body called the aorta.
- The (ascending) aorta leaves the heart in the middle of the chest and makes a U-turn (aortic arch) beneath the level of the collar bone to head downwards in the middle of the chest, next to the spine.
- As it makes the U-turn major and important arterial branches are given off to supply the head, neck, face and brain.
- In the chest, the (thoracic) aorta gives numerous side-branches (intercostal arteries) at every level of the rib spaces, and eventually passes through the diaphragm to become the abdominal aorta.
- In the abdomen, the abdominal aorta gives three forward branches (celiac, superior and inferior mesenteric arteries – that supply the digestive system), two lateral branches (right and left kidney/renal arteries) before dividing into its two terminal branches at the level of the belly button (umbilicus) – the right and left common iliac arteries.
- From this point, the internal iliac arteries supply the pelvis, while the external iliac artery branches continue on into the lower extremities as the femoral (thigh), popliteal (knee) and tibial arteries (leg).
An artery is considered aneurysmal if the dilation is greater than 1.5x the reference vessel diameter.
Aneurysms can occur anywhere in the arterial tree, hence its presentation can be as varied as is its myriad of clinical problems.
Most aneurysms are caused by degeneration of the vascular wall integrity.
There are 3-layers that make up the arterial wall (from outer to inner: adventitia, media, intima), and the commonest type of aneurysm is due to atherosclerotic degeneration and elastin deficiency within the middle (media) layer of the wall.
Most of these aneurysms have a fusiform configuration where the area of weakness is circumferential and the affected arterial segment bulges uniformly. Dissecting aneurysms are thought to be a variant of degenerative aneurysms where the diseased artery with a defect or tear in the intima or media succumbs to the forward pulsatile flow of blood contained within arteries, causing subsequent propagation of this tear along the different layers of the artery.
Aneurysms can also be caused by bacterial infections (Salmonella, Streptococcus, Staphylococcus, E-coli, Treponema) and these are called mycotic aneurysms. These sometimes weaken only a patch of the artery wall leading to a saccular appearance, where part of the wall is normal and the affected part bulges out eccentrically.
Saccular or mycotic aneurysms are generally considered slightly more dangerous and are more prone to undesired complications.
Pseudoaneurysms or ‘false aneurysms’ are formed when bleeding from an area of the artery is contained within the soft tissue, causing a pocket of swirling blood that is in communication with the flowing artery. This soft tissue pocket and cavity does not have any true arterial wall and is prone to rupture and bleeding if it is close to the skin. Pseudoaneurysms can result from penetrating injuries like stabbing, gun shots, or surgery.
Aneurysms generally do four bad things
1) expand, leading to a mass effect and pressure on the adjacent structures
2) rupture, bleeding, exsanguination, leading to limb loss of death
3) accumulation of clots/sediments that break off, flow along (embolize), and plugs off blood supply
4) the whole aneurysm clots off, cutting off blood supply of the artery downstream
Expansion can cause extrinsic compression on adjacent structures such as nerves and veins that usually travel together with arteries.
Cerebral (brain) aneurysms involving the Anterior Communicating Artery can compress on the optic chiasm (main nerve for eye-sight) causing visual defects. Posterior Communicating Artery aneurysm can affect the Occulomotor nerve causing eye lid drooping, weakness of muscles that normally move the eyeball, and persistent pupil dilation. Any persistent headaches associated with eye- or visual-disturbances therefore need to be investigated to rule out cerebral aneurysms.
In the chest and abdomen, aortic aneurysms can cause pain if they press on the spine and/or nerves. Behind the knee, Popliteal aneurysms can be large enough to compress and impede venous blood return leading to deep venous thrombosis (DVT).
Along the lines of continued expansion, the larger the aneurysm diameter, according to Physics and Poiseuille’s law, the greater the wall shear stress and propensity for rupture. If aneurysm rupture occurs, two devastating things can happen: 1) bleeding or exsanguination which can be life-threatening, perhaps culminating in the most extreme complication – death, 2) cessation of blood flow/supply beyond the point of rupture leading to ischemia, organ failure, or limb loss.
If rupture occurs in the brain, patients suffer a stroke (subarachnoid hemorrhage, intracranial hemorrhage). In the chest or abdomen, aortic aneurysm ruptures frequently results in death due to rapid and brisk bleeding. In the abdomen, vital organs such as kidneys and intestines can become non-viable, life-threatening and urgent surgery is needed for survival.
Blood flow within arteries is usually from larger to smaller vessels, as more arterial branches are given off along the way. Aneurysms pose an area of dilation and larger diameter where blood flow slows down and eddy current form at the periphery. This can lead to accumulation of clot (mural thrombus) on the internal surface of the aneurysm wall. Some of these can break off, flow along (embolize) until it plugs into an artery or branch which is too small for it to pass through. This leads to ischemia (lack of blood supply) to the organs distally.
Distal embolization can be seen in kidney or spleen infarcts (patchy non-viable tissue) due to thoracic aneurysms. Abdominal aortic aneurysms can cause shower embolization to toes and feet, cutting off blood supply to toes and feet (blue toes syndrome mandates investigations higher upstream).
Certain peripheral aneurysms can clot off altogether (thrombosis) if the mural thrombus load is high. Popliteal aneurysms are notorious for this phenomenon, which pose a high risk for limb loss (40 percent) and leg amputation.
Management of aneurysms
Management of aneurysms starts with awareness, clinical index of suspicion, appropriate investigations, leading to comprehensive surgical care: either open vascular surgery or minimally invasive endovascular surgery.
Aneurysms are very treatable diseases and should be taken care of by vascular specialists who will begin with a detailed History and Physical Examination. Some aneurysms have a familial preponderance (e.g., cerebral aneurysms and Abdominal Aortic Aneurysms/AAA), and some can co-exist (e.g., Popliteal aneurysm have a 40 percent association with AAA).
Usually some form of imaging test is necessary for diagnostic and therapeutic planning, the simplest in the form of Duplex Ultrasound scan; however increasingly more contemporary practices consider CT-aortogram or arteriogram as a ‘gold standard’ in terms of imaging techniques.

Depending on the location of the aneurysm, patient characteristics, preferences, and available technology, most aneurysms can be repaired with open vascular surgery (aneurysm exclusion/endoaneurysmorrhaphy and bypass) or endovascular (minimally invasive) repair with endografts, covered-stents, or coil-embolizaton.
Article and pictures contributed by Dr John Wang, Vascular and General Surgeon at PanAsia Surgery.