Dr. Raj discussed an interesting case of a patient presenting with abdominal pain who was ultimately diagnosed with a mycotic aneurysm: as such, she was able to touch on several great teaching points.
#1- What is a mycotic aneurysm and what are the risk factors?
A mycotic aneurysm is any infected abnormal focal arterial dilation, the majority of which are bacterial in nature. Mycotic aneurysms can either occur when a pre-existing aneurysm is infected or the infection of the arterial wall can actually result in a primary aneurysm.
There are several mechanisms by which a mycotic aneurysm can occur:
Direct bacterial inoculation — Bacteria can be directly inoculated in the wall at the time of a vascular injury (central line placement, injection drug use, gunshot, etc.). The femoral artery is the most common location.
Bacteremic seeding- A bacteremic patient can seed an existing injury, plaque, or aneurysm.
Contiguous infection — A pre-existing focus of infection can extend to the arterial wall.
Septic emboli — In a patient with bacterial endocarditis, septic embolic from the heart can occlude the vasa vasorum of the vessel or the vessel lumen, leading to vascular wall infection and mycotic aneurysm formation.
The following are risk factors for mycotic aneurysms:
Pre-existing Arterial injury or aneurysm.
Antecedent infection – classically pneumonia, cholecystitis, UTI, endocarditis, diverticulitis, soft tissue infection, or osteomyelitis.
Atherosclerosis
Immunosuppression-Don't forget about less obvious causes of immunosuppression including chronic steroid therapy and alcoholism.
#2- How should we screen for AAA?
First, let's review what an AAA is. An abdominal aortic aneurysm (AAA) is considered to be present when the minimum anteroposterior diameter of the aorta reaches 3.0 cm. Risk factors for this condition include smoking, male sex, and increasing age as well as atherosclerosis, hypertension, and family history of AAA.
The USPSTF makes recommendations on screening for AAA: one-time screening with ultrasound should be performed in men age 65-75 who are active or former smokers.
#3- When do I need to send my patient to have his AAA repaired?
Once an AAA has been identified, surveillance is needed because the strongest risk factor for the rupture of an AAA is maximal aortic diameter; this measurement is the dominant indication for repair. Additionally, because larger aneurysms expand faster than smaller ones surveillance is more frequent.
If AAA maximum diameter is 3.5 to 4.4 cm, repeat ultrasonography is recommended annually.
If AAA maximum diameter is 4.5 to 5.4 cm, repeat ultrasonography should be performed every 6 to 12 months.
Elective repair should be considered for
Symptomatic patients (abdominal or back pain)
AAA of 5.5 cm in diameter in men; 5.0 cm for women.
AAA that increase in diameter by more than 0.5 cm within a 6-month interval
References
https://www.uptodate.com/contents/overview-of-infected-mycotic-arterial-aneurysm
MKSAP 17: Diseases of the Aorta.
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