An aneurysm is an abnormal focal arterial dilation. Preexisting aneurysms can become secondarily infected, but aneurysmal degeneration of the arterial wall can also be the result of infection that may be due to bacteremia or septic embolization, as in the case of mycotic aneurysm. The name mycotic aneurysm was coined by Osler to describe aneurysms associated with bacterial endocarditis . These were noted to have the appearance of "fresh fungus vegetations"; however, the majority of mycotic aneurysms are caused by bacteria. Although some authors use the term "mycotic" to describe infected aneurysm regardless of etiology, we will limit the use of this term to those aneurysms that develop when material originating in the heart causes arterial wall infection and, subsequently, dilation .
Aneurysms are classified into true and false, or pseudoaneurysms. True aneurysms involve all three layers of the arterial wall (intima, media, and adventitia). A false, or pseudoaneurysm, is a collection of blood or hematoma that has leaked out of the artery but is then confined by the surrounding tissue.
Infected aneurysm is a serious clinical condition that is associated with significant morbidity and mortality. Treatment consists of antibiotic therapy combined with aggressive surgical debridement of the infected tissue and vascular reconstruction, as needed. Endovascular therapies may have a role in the treatment of ruptured infected aneurysm and the treatment of patients at prohibitive risk for open surgery.
The pathogenesis, microbiology, clinical manifestations, diagnosis, and treatment of infected aneurysms will be reviewed. The diagnosis and management of noninfected aneurysms are discussed in separate topic reviews. (See "Iliac artery aneurysm" and "Popliteal artery aneurysm" and "Management of asymptomatic abdominal aortic aneurysm".)
Risk factors for infected aneurysm include: