**1. Introduction**

Infected aortic aneurysms, also known as "mycotic aortic aneurysms" (or microbial arteritis with aneurysms) are most commonly caused by bacterial infections. Around 1% of arterial aneurysms may be associated with an arterial infection. Although the prevalence of mycotic aortic aneurysms (MAAs) is low, its clinical impact may be severe and represents one of the most difficult arterial diseases to treat successfully.

In the early nineteenth century, Jean Nicolas Corvisart coined the term "vegetation" as it resembled a cauliflower, describing organic lesions of the heart. In his monograph, presented in 1806, Corvisart wrote that he had observed six cases of valve disease with vegetations [1].

Some years later, in 1815, Joseph Hodgson performed some illustrations of ulcerating/perforating aortic valve endocarditis. He described the valve vegetations as "wart-like excrescences" using the term "fungus" in a patient who presented with an aortic root abscess. This report was probably the first to document peripheral embolization [2].

In 1852, a British physician, William Kirkes, described that fibrinous fragments of valve vegetations were found in the kidneys, cerebral artery, and spleen in patients presenting with fever, heart murmur, purple skin spots, and skin nodules (later called "Osler nodules" by Emanuel Libman). He described how these fragments could be detached from the heart valves, passed into the blood, and may be arrested in the aorta or its branches [3, 4].

The suggestion of an infection point of entry and transportation by blood flow was reinforced by a pioneering microbiologist, Edwin Klebs. In 1878, he suggested that cases of endocarditis were always due to an infectious organism [5].

The first complete description of an infected aneurysm was presented in 1885 by Osler. He presented the first broad report of this entity with a complete description of clinical and anatomical features of infective endocarditis as the cause of these arterial infections. The report included clinical features, anatomical location in the aorta, and cases of "ulcer formation and perforation of the aorta with production of multiple aneurysms" [6].

There were some other early reports that explained how infected aortitis was nearly always secondary to endocarditis [3, 5, 7, 8]. In another report published in 1923, a series of 217 patients with mycotic aneurysms was presented, showing that 86% of mycotic aneurysms were associated with infective endocarditis [9]. Although most infected aneurysms are due to bacterial infections, the term "mycotic," which is still misleading, is used to describe these aneurysms that arise after an inflammatory destruction of the arterial wall happens associated to arterial embolization. A wide variety of terminologies have been used to describe infected aortic aneurysms, although most of them have not received a great acceptance. Some of these include mycotic aortic aneurysms (MAAs), suppurative arteritis, septic aortic pseudoaneurysm (SAP), cryptogenic mycotic aneurysm, and microbial arteritis with aneurysms [10–13].

## **2. Etiology**

**Table 1** includes a previous classification of infected aneurysms (**Table 1**) [14]. The main etiology of MAAs is considered to be similar to that of arterial aneurysms and includes the following:

1.*Contiguous infection*: an infection localized in a determined area might extend and affect the arterial wall. This can happen after bone infections (osteomyelitis and vertebral infections), intraabdominal infections, abscesses, pancreatitis, and pancreatic pseudocysts. Arterial aneurysms have been described after surgical procedures such as a cholecystectomy, appendectomy, knee replacement surgery, or intestinal surgery [15, 16].


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*Mycotic Aortic Aneurysms*

*DOI: http://dx.doi.org/10.5772/intechopen.86328*

symptomatic MAAs [17].

plaques.

**3. Risk factors**

**4. Epidemiology**

following:

common location of primary arterial infection.

(UTI), soft tissue infections, and osteomyelitis.

2.*Arterial injuries*: previously described in etiology.

2.*Bacteremic seeding*: all arterial layers can be affected by bacteremic seeding, which may occur when there is a preexisting aneurysm, atherosclerotic plaque, or intimal injury. The intima is usually resistant to infection. Once it becomes diseased, bacteria may progress through it into other layers (media or adventitia). As the aorta is the most frequent site of atherosclerosis, it is also the most

3.*Septic embolism*: embolization from heart chambers secondary to endocarditis (vegetations) can affect the intimal layer or vasa vasorum of vessels, leading to arterial wall infection and MAA formation. Embolization may occur in between 25 and 50% of patients with endocarditis, but only 1–5% develop

4.*Direct bacterial inoculation*: infected pseudoaneurysms after arterial injuries have become a common cause of mycotic aneurysms. The common femoral artery (CFA) is the most frequently affected vessel. Vascular trauma, gunshot or stab wounds to arteries, intra-arterial drug injection, and iatrogenic arterial injuries can produce a direct inoculation of bacteria into the vessel wall. Infected pseudoaneurysms resulting from drug injection using dirty needles may involve the CFA, external iliac, subclavian, and carotid arteries [18].

5.*Atherosclerosis*: MAAs may arise from preexisting aneurysms or atherosclerotic

Some important risk factors for development of MAAs include some of the

3.*Immunosuppression*: certain diseases and treatments may lead to impaired immunity states, including chronic corticoid use, alcohol abuse, diabetes mel-

Infected arterial aneurysms are relatively uncommon and can affect very different anatomical location and practically any artery. Depending on different studies presented in the literature, the most common sites for mycotic arterial aneurysms are the aorta and the intracranial cerebral arteries. Following Baddour publication in 2015, regarding an American Heart Association (AHA) statement report on infective endocarditis (IE) in adults, the most common site of mycotic aneurysms was the intracranial arteries, with an incidence of 1.5–5% of cases, and an overall mortality among those with IE of 60% [17]. Some other series have reported similar

litus, malignancy, chemotherapy, and severe neutropenia.

1.*Infection*: other sources of infection are the main cause of MAAs. Still today, the most common cause of MAAs is endocarditis, which explains more than 30% of cases [17]. The second most common infectious cause of MAAs is bacteraemia. Other infections have also been reported and associated to MAAs, including cholecystitis, pancreatitis, diverticulitis, urinary tract infections

#### **Table 1.** *Modified classification of infected aortic aneurysms according to Wilson et al. [14].*

### *Mycotic Aortic Aneurysms DOI: http://dx.doi.org/10.5772/intechopen.86328*

*Aortic Aneurysm and Aortic Dissection*

multiple aneurysms" [6].

arteritis with aneurysms [10–13].

and includes the following:

Bacteriology *Gram-*

*M: Male. F: Female.*

ment surgery, or intestinal surgery [15, 16].

**Infected aneurysm**

*Staphylococcus aureus, Escherichia coli*

*Modified classification of infected aortic aneurysms according to Wilson et al. [14].*

**Mycotic aneurysm**

*positive cocci*

**2. Etiology**

The suggestion of an infection point of entry and transportation by blood flow was reinforced by a pioneering microbiologist, Edwin Klebs. In 1878, he suggested

The first complete description of an infected aneurysm was presented in 1885 by Osler. He presented the first broad report of this entity with a complete description of clinical and anatomical features of infective endocarditis as the cause of these arterial infections. The report included clinical features, anatomical location in the aorta, and cases of "ulcer formation and perforation of the aorta with production of

There were some other early reports that explained how infected aortitis was nearly always secondary to endocarditis [3, 5, 7, 8]. In another report published in 1923, a series of 217 patients with mycotic aneurysms was presented, showing that 86% of mycotic aneurysms were associated with infective endocarditis [9]. Although most infected aneurysms are due to bacterial infections, the term "mycotic," which is still misleading, is used to describe these aneurysms that arise after an inflammatory destruction of the arterial wall happens associated to arterial embolization. A wide variety of terminologies have been used to describe infected aortic aneurysms, although most of them have not received a great acceptance. Some of these include mycotic aortic aneurysms (MAAs), suppurative arteritis, septic aortic pseudoaneurysm (SAP), cryptogenic mycotic aneurysm, and microbial

**Table 1** includes a previous classification of infected aneurysms (**Table 1**) [14]. The main etiology of MAAs is considered to be similar to that of arterial aneurysms

1.*Contiguous infection*: an infection localized in a determined area might extend and affect the arterial wall. This can happen after bone infections (osteomyelitis and vertebral infections), intraabdominal infections, abscesses, pancreatitis, and pancreatic pseudocysts. Arterial aneurysms have been described after surgical procedures such as a cholecystectomy, appendectomy, knee replace-

Etiology Endocarditis Bacteremia Bacteremia Traumatic Bacteremia Location Any vessel Distal aorta Aortoiliac Femoral, carotid Aortoiliac Age 30–50 >50 >50 <30 >50 Sex F > M M M M/F M/F Incidence Rare Unusual Common Common Unusual Number Multiple Single Single Multiple Multiple

**Microbial arteritis**

**Traumatic infected pseudoaneurysm**

*Salmonella Polymicrobial*

**Contiguous septicemia**

that cases of endocarditis were always due to an infectious organism [5].

**48**

**Table 1.**

