Mycotic Aneurysm
What is Mycotic aneurysm?
The mycotic aneurysm is a type of aneurysm that appears as the wall of certain arteries suffers from a bacterial infection. This medical condition is often perceived as a complication of the infection – the bacteria travels from the heart, the hematogenous spread being responsible for the mycotic aneurysm.
This condition is also known as microbial arteritis, having been identified for the first time by Osler in 1885. Out of all the aortic aneurysms, the mycotic aneurysms account for 2.6%. The earlier the diagnosis is made, the better the prognosis will be. As you will have the opportunity to read below, the lack of treatment can be fatal, with hemorrhaging and sepsis being among the most common consequences.
The diagnosis of the mycotic aneurysm during the early stage is quite difficult, due to the fact that the majority of the symptoms are non-specific. It is also important to mention that the mycotic aneurysm can appear as a complication of other medical problems, such as is the case with the infective endocarditis.
You will often see the mycotic aneurysm presented as a false aneurysm (also known as pseudoaneurysm). The true aneurysm occurs when all of the three layers of the arterial wall are involved. These three layers are the intima, media and adventitia. On the other hand, the false aneurysm refers to a collection of blood that has leaked out of the artery but it is confined by the tissues that surround it.
Pathology
When the bacteria reaches the walls of the arteries, it starts to digest it, leading to the appearance to what clearly is a false aneurysm. It should be mentioned that the mycotic aneurysm is characterized by a high degree of instability, with an increased risk for rupture.
The most common mechanisms of infection include: septicemia, adjacent infection (contiguous spread) and septic emboli. There are also risk factors to be considered for the mycotic aneurysm, such as: state of bacteremia, infectious endocarditis, drug abuse (with intravenous administration), state of reduced immunity, aortic trauma or iatrogenic causes, atherosclerotic plaque (pre-existing), native aneurysm (pre-existing) and prosthetic arterial devices (stents or grafts).
As for the most often identified bacterial agents that lead to the appearance of the mycotic aneurysm, these are salmonella, staphylococcus aureus and Klebsiella pneumonia. The latter is more and more often identified as a pathogen leading to the mycotic aneurysm. This can also lead to other health problems, such as the abscess of the liver, spleen or endophthalmitis. Gram-negative bacilli can also cause such health problems, with a preference for the infrarenal sites (often encountered in elderly patients).
The mycotic aneurysm is identified in areas where one would expect the least, such as: aorta (thoracic or abdominal), visceral arteries of the abdomen, arteries of the lower extremities and intracranial arteries (peripheral location, as opposed to the berry aneurysms).
Diagnosis
These are the methods used for the diagnosis of the mycotic aneurysm:
CT or CT angiography
- The location of the aneurysm is atypical (thus excluding the diagnosis of atheromatous disease)
- The aneurysm can present a multilobulated appearance
- The calcification of the arterial wall is interrupted by the aneurysm
- If aorta – rupture of the wall
- Fluid collection and thrombus formation.
The differential diagnosis can be made with other types of aneurysms, such as the atherosclerotic aneurysm and the inflammatory aortic aneurysm.
Treatment
In the situation that the mycotic aneurysm becomes infected, there is a high risk of morbidity and mortality. The treatment measures taken for such measures include the administration of antibiotics, followed by the aggressive surgical debridement of the tissue that has been infected. The surgical intervention is generally completed by the vascular reconstruction. It is possible that the endovascular approach is chosen as treatment for the mycotic aneurysm – this is recommended in patients for whom the open approach is not suitable and also in case of aneurysm rupture.
The size of the mycotic aneurysm may dictate the need for treatment. It is known that small mycotic aneurysm may resolve spontaneously, thus requiring no treatment or surgical intervention. The mycotic aneurysm that have over 1-2 cm in diameter are required to be surgically removed.
Pictures of Mycotic aneurysm
Picture 1 : Diagram showing the Saccular aneurysm, Atherosclerotic aneurysm, Mycotic aneurysm(bottom left) and Traumatic aneurysm
Prognosis
Due to the high mortality rate, the mycotic aneurysm does not present a very good prognosis. The mycotic aneurysm that present a high risk for morbidity or mortality often affects those whose immune system is compromised; it also appears in those who suffer from pre-existing conditions, such as heart disease or atherosclerosis. The elderly patients present mycotic aneurysms that are located at infrarenal sites, while those who are younger present a high risk for intracranial aneurysms.
Complications
A number of complications can arise in patients who suffer from a mycotic aneurysm, such as: rupture of the aneurysm (high risk, leads to hemorrhage), sepsis (the aneurysm is an ongoing source) and embolic infarction.
