Chapter 48: Native Arterial Infections

INTRODUCTION

Epidemiology

Native arterial infections are a condition that implies destruction of the native arterial wall by an infectious process. This may result in sepsis, compression, erosion, embolization, thrombosis, hemorrhage, or pseudoaneurysm formation. Osler et al. first presented the relationship between arterial infections and aneurysm formation in 1885, where he coined the phrase “mycotic aneurysm” in reference to a young patient who was found to have endocarditis of the aortic valve as well as multiple aneurysms of the thoracic aorta on autopsy.¹ The name mycotic aneurysm was chosen by Osler for aneurysms associated with bacterial endocarditis for its similar appearance to fresh fungal vegetations. The term has come to be associated with both true and false aneurysms that are associated with infection of the arterial wall. Mycotic aneurysms carry a high rupture rate and should be considered an urgent medical condition.

Pathogenesis

Five basic mechanisms of primary arterial infections have been designated.² These mechanisms can be summarized as:

1. Oslerian mycotic aneurysms: Unique clinical condition characterized by bacterial endocarditis with septic embolization from valvular vegetations. A primary mycotic aneurysm is not associated with septic emboli from cardiac valve vegetations, but instead is associated with bacteremia that can cause seeding of normal artery or already established aneurysm. Additionally, the arterial wall can be contaminated with bacteria from direct trauma or a contiguous site of infection.

2. Microbial arteritis with aneurysm formation: Hematogenous microbial seeding of arteries during an episode of bacteremia. The artery can be normal or atherosclerotic and becomes infected, weakening the arterial wall and causing aneurysm formation.

3. Infected aneurysms: Infection of a preexisting aneurysm, often by hematogenous spread and seeding of the arterial wall. While predominantly bacterial, they may also be caused by fungal or viral infection, such as in advanced human immunodeficiency virus (HIV) infection.³

4. Arterial injury with contamination: Mechanical arterial injury caused by infected/contaminated surgical instruments during radiologic procedures, drug injection, vascular access, or as a result of traumatic injury.

5. Arteritis from contagious spread: Spread from surrounding structures such as osteomyelitis, tuberculous lymph nodes, or narcotic injection-associated abscesses.⁴

The organism most commonly associated with microbial aortitis and Oslerian mycotic aneurysms is Salmonella, with decreasing frequency of Streptococcus, Bacteroides, Arizona hinshawii, Escherichia coli, and Staphylococcus aureus.² Femoral aneurysms and intravenous (IV) drug abuse-associated aneurysms are more commonly of the gram-positive species Staphylococci and Streptococci, with E. coli and Pseudomonas also being common. The presence of rheumatic fever and bacterial endocarditis has decreased over time in the post-antibiotic era. In a review published in 1986, the most common organisms in endocarditis found in patients with a history of IV drug abuse were S. aureus (36%), Pseudomonas species (16%), polymicrobial organisms (15%), Streptococcus faecalis (13%), and Streptococcus viridans (11%). In non-IV drug abusers, the most common organisms in endocarditis were S. viridans (22%), S. aureus (20%), ...