Aneurysm is an unusually big bulge which can occur because of the weakening of the artery’s wall, also it can occur in veins but it is less common because of the low pressure. Aneurysm could happen in any part of our body. However, they are most common in the aorta, brain, spleen, and the legs. Aneurysms are classified by their causes and characterized based on the aneurysm location, size, and morphology.
There are two major categories of aneurysms: true aneurysm and psuedoaneurysm. In true aneurysm all the layers of the vessel dilate together for a short distance, true aneurysms which bulge symmetrically on all sides of the aneurysm are called fusiform and if the dilating involves a longer length of the vessel walls, it is called cylindrical. Whereas asymmetrical true aneurysms which is called saccular or berry, bulge to only one side of the blood vessel and it is occur because one side of the blood vessel has had to put up with higher blood pressure than the rest of the vessel wall or because the wall was weaker to begin with. Psuedoaneurysm can be can be also called false aneurysm, because it is caused by a small hole in the blood vessel which will make the blood able to leak out of the blood vessel and form a collection of blood that looks like a fusiform or saccular depending on the location of the hole and the size of it, the blood form a collection because the surrounding tissues act like a wall that contains the blood in one spot.
Arterial aneurysm occur most commonly in the aorta with about 60% of true aortic aneurysms happening in the abdominal section the aorta and about the other 40% happening in the thoracic section. 95% of all the true aortic aneurysms are found in the part below the point where the renal artery branch of from the abdominal aorta but above the aortic bifurcation, that’s because there is naturally less collagen in the walls of this part of the aorta than the rest of the aorta.
Aneurysms can be caused by anything that leads the vessel walls to become weak. When the vessel wall weakens it will struggle to maintain the pressure of the blood pushing, so the diameter of the blood vessel lumen increases. On the top of this the pressure on the vessel wall increases as the diameter of the lumen increases because of Laplace’s law. One of ways that leads the blood vessels to become weak is not receiving enough oxygen and this can be caused by hypertension or arthrosclerosis. Some bacterial infections can also cause aneurysm which is called mycotic aneurysms. The bacteria from an infection somewhere else in the body can break of from the main infection and travel around in the blood, usually it stuck in the intracranial arteries, visceral arteries, or the arteries which supply the arms and the legs leading to an aneurysm.1,2,3
Most unruptured aneurysms are asymptomatic, and the anterior communicating artery being the most common site of cerebral aneurys . Depending on the site of aneurysm, it can compress neurologic structures giving rise to specific symptoms which may indicate the location such as, third nerve (oculomotor) palsy involving the pupil, but in most cases it is diagnoses incidentally in routine checks for other diseases or when it is ruptured. There are three main approaches when it comes to diagnosing a suspected aneurysm, which are computed tomography angiography(CTA), magnetic resonance angiography(MRA), and digital subtraction angiography(DSA).4
First of all, the first line technique used in case of a ruptured aneurysm which caused a subarachnoid hemorrhage is the non-contrast-enhanced CT scan, in the first 6 hours of hemorrhage, it has a 100% sensitivity, but it decreases with time since the brain will start to degrade the blood clots leading to less sensitivity, it can drop to 50% after 1 week of the hemorrhage. Thus, if the patient was too late after the onset of hemorrhage, an additional lumbar puncture is indicated to evaluate the presence of red blood cells in the cerebrospinal fluid, which is called xanthochromia, otherwise CT angiography(CTA), can be also used, if both are negative then there is a negative post-test probability of 99.43%. Moreover, CTA has a reliable diagnosis of aneurysms that are more than 4mm up to 100% sensitivity, for smaller aneurysms a 320-slice CT has to be taken to reach a sensitivity of 81.8%.4
Secondly, MRI, is not the thirst diagnostic choice of diagnosing aneurysms or subarachnoid hemorrhage since it is very expensive and it takes longer time, but it can be the first choice for patients with renal failure and contrast allergy. Recent studies have showed that MRA has a sensitivity up to 100% in subacute hemorrhage with using FLAIR technique.4
Finally, Digital subtraction angiography(DSA), which uses femoral catheterization to inject iodinated contrast in main cerebral arteries while producing different 2D and 3d images of the vessels. In comparison with MRA and CTA, DSA has a higher spatial resolution which can detects aneurysms missed by using MRA and CTA. However, it is an invasive technique requiring ionizing radiation and iodinated contrast as CTA, but more expertise are needed in DSA to minimize the risk of re-hemorrhage, stroke, and femoral artery occlusion. 4
The most common and dangerous complication that can develop into the intracranial aneurysms is the rupture and bleeding. This leads to subarachnoid hemorrhage (SAH) that has a high rate of mortality and morbidity. Therefore, it is important to treat an aneurysm based on the possibility of rupturing. Moreover, because the chances for recurrent is higher after each subarachnoid hemorrhage (SAH) reaching 3 to 4 percent in the first day and 1 to 2 percent in the first month, the treatment of the aneurysms is divided mainly to unruptured and ruptured aneurysms. There are two main treatment options for both types that is clipping which is a microsurgical procedure and coiling which is an endovascular procedure. There has been a lot of debate around which procedure is better but in reality, it is a cooperation work of the treatment team to decide which procedure is most suitable for each case based on mainly experience rather than researches and theories. 5
Endovascular treatment has included many procedures and most importantly is the coiling. Coiling involves putting a catheter in an aneurysm and coiling it. There is also a stent-assisted and balloon-assisted. These are adjuncts to help during the procedure. In addition, recently flow diverters were introduced which don’t go inside an aneurysm rather around it and has a special type of stents that changes the flow within the aneurysm.
Microsurgical treatment has been used way before the endovascular procedure and has also develop newer procedures over the years. Clipping is using a very small clip and places it on the neck of the aneurysm to block the connection and flow between the blood vessel and the aneurysm. New developments in the field of technology have also aided the development of more accurate and lower risks during this clipping procedure. One is the surgical theater, which is a 3-dimensional modeling of the actual aneurysm developed by the UH University in Cleveland using a CT scans angiogram of the patients to investigate the surgical perspective of the aneurysm from different angles and follow the location and surrounding structures as well. Another development in this field is the indocyanogreen angiography, that allows the surgeon to evaluate whether the aneurysm is blocked or not and if other structures like nerves are affected as well by placing the clip. Microsurgery is much harder intervention than the endovascular procedure. 6
Although experience and judgment of the surgeon are important, guidelines are important to show an evidence about the treatment approach. In 2015, the American heart association (AHA) has published guidelines concerning the management of intracranial aneurysms 7. For the unruptured aneurysm, clipping has shown to be very effective based on class1B level evidence. On the other hand, endovascular coiling was also effective but based on class 2B evidence which a lot of considerations needs to be made before choosing it to include aneurysm size, location, and the surgeon endovascular experience. All patients need to be informed about the risks and benefits of the treatment procedure beforehand. Furthermore, the endovascular coiling has shown a reduction in the morbidity and lower mortality rate, but the problem is that there is a high rebleeding risk in compared with clipping. Part of the reason is, the packing density of the coil is usually posterior 40% of the aneurysm and this means that only part of the aneurysm is filled, thus if the neck of the aneurysm is large enough it can shift the coil and part of it will start refill again.
The guidelines for the ruptured aneurysm has been made too. The microsurgical clipping and endovascular coiling are both equally feasible options and coiling should be considered. However, it depends on each patient case. For example, clipping should be considered for young patients because the durability is higher for clipping than coiling. For elderly and comorbidity patients, the survival rate is less than 25%, so coiling should be considered since it has lower morbidity chances.
From the overall look at both procedures, a person can say that coiling would be a better choice if it was applicable. Nevertheless, as it said before each case has different considerations that may alter the choice of treatment. In some cases, the complexity can be high for both coiling and clipping such as ruptured blister aneurysm in which the aneurysm is very small has thin membrane that a clip might lead to rupture, the coiling needs a microcatheter to deliver the coil and because of the antiplatelet regimens that are usually associated with, flow diverters or stents will be hard to use too. In other cases, clipping can be the better option, like very large aneurysms or calcified neck. 8