Aetiology of infected aneurysms

Infected aneurysms (also known as mycotic aneurysms) can be characterised anatomically as:

• intracavitary (within the thorax or abdomen)
• peripheral (primarily in the extremities and, less commonly, in the carotid arteries)
• intracranial.

Infected intracavitary aneurysms are most commonly caused by Staphylococcus aureus, coagulase-negative staphylococci, nontyphoidal Salmonella species and streptococciLin, 2014Sorelius, 2016. Other rare causes include Haemophilus species, anaerobes and mycobacteria. In some cases, culture results are negative; see Culture-negative endocarditis for pathogens to consider in these cases.Wilson, 2016

Patients with infected peripheral aneurysms often have a history of injecting drugs. Infected peripheral aneurysms occasionally develop following trauma or a vascular procedure, or in patients with infective endocarditis. S. aureus is the most common pathogen and is often methicillin-resistant. Other pathogens include gram-negative bacilli and fungi. People who inject drugs can have polymicrobial infectionsWilson, 2016.

Infected intracranial aneurysms are usually associated with infective endocarditis. Infection can also result from contiguous spread from infected meninges, cavernous sinus or sinusitis. S. aureus and viridans streptococci are the most common pathogens, but many other pathogens can be involvedAlawieh, 2018Ducruet, 2010Wilson, 2016.