**4. Epidemiology**

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 findings, with intracranial arteries being the most common site for mycotic aneurysms (especially the middle cerebral artery), with and incidence of symptomatic peripheral mycotic aneurysms of 1–5% [19].

Some other reports have published that the higher incidence sites of infected aneurysms are the abdominal aorta, followed by peripheral arteries (typically occurring at bifurcation sites), cerebral arteries, and visceral arteries, in descending order of frequency [20]. On the other hand, previous historical series have reported that the abdominal aorta was the second most common site of aneurysm infection, with the common femoral artery being the most common site [21].

Mycotic aneurysms of coronary arteries are rare, but have also been described. González et al. performed a review including 922 cases of definite infective endocarditis (IE), and reported a 2% rate of symptomatic peripheral mycotic aneurysms. In their review, 66% of mycotic aneurysms were intracranial (in the region of the middle cerebral artery) and 34% were extracranial [19].

With regard to infected aneurysms of the aorta, most reported series have less than 50 patients. Most series concur that the most common aortic location for infected aneurysms of the aorta is the infrarenal aorta, with a similar distribution of cases between the aortic arch and descending aorta.

One of the largest series involving MAAs presented 36 cases of aortic infection, with the following epidemiology data: infrarenal aortic aneurysm in 15 patients (42%), a suprarenal aneurysm in 3 (8%), a thoracic aneurysm in 5 (14%), and a thoracoabdominal (TAAA) in 13 (36%) [22].

A large multicenter European study was published in 2014, where data from 123 patients with 130 identified MAAs were analyzed. Similar epidemiologic findings were found, with infrarenal location being the most common (51%), followed by descending MAAs (28%), paravisceral (12%), multiple MAAs (6%), and arch MAAs (3%) [23].

Primary MAAs are a challenging and very complex vascular pathology. Although they represent a small proportion of patients within all aortic aneurysms, when left untreated, they almost always develop into rupture or lethal complications. Without treatment, there is a very high level of lethal complications, including aortic rupture, abscess formation, and sepsis [17].

### **5. Microbiology**

With regard to bacteriological patterns in infected aortic aneurysms, there have been some changes in bacterial patterns depending on the published series decade. Some initial studies on aortic infection have presented their results confirming *Staphylococcus aureus* as the most common infectious cause, followed by *Salmonella* organisms [24]. A series of 17 patients with MAAs reviewed in 1998 presented *Staphylococcus aureus* as the most common responsible organism (29% of patients), followed by *Salmonella* organisms (24% of patients) [25].

This change in bacteriologic patterns was already observed in the early 1980s, when comparing those series from before 1965 and those from after 1965. Collected series from English language reported before 1984 (178 patients with 243 MAAs) showed that *S. aureus* was the most common organism (28% of cultures), followed by *Salmonella* (15% of aneurysms) and Streptococcus (10% of patients). This series reported how there was some alteration in the involved bacterial flora before and after 1965. A decrease in the incidence of *Salmonella* infections was seen after 1965 (10% compared with 38% prior to that date), as well as an increase in the incidence of *Staphylococcus aureus* (from 19 to 30%) [21].

Some current series have presented a much higher incidence of Gram-negative organisms compared with older series, with Gram-negative microorganisms seen in up to 35%

**51**

following:

1.Rupture

2.Expanding hematoma

*Mycotic Aortic Aneurysms*

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

*Salmonella*-aortic infections [23, 27–29].

onset, apathy, weight loss, and general malaise [24].

rupture in MAAs in 50–85% of patients [24, 28, 31].

massive hemorrhage due to rupture [24, 31].

**6. Clinical presentation**

of cases. Different groups have described a higher incidence of aneurysm rupture and mortality in those patients with Gram-negative infections compared with Gram-positive organisms. Aortic aneurysms with *Salmonella*-related infections have been associated with a faster progression and higher risk of early rupture [23]. Recent series have published an increase in Gram-negative bacteria in MAAs, including *Salmonella*, *E. coli*, *Campylobacter*, *Enterobacter*, *Serratia*, and *Proteus* [23, 26]. Some of these series have reported even higher

rates in Gram-negative bacteria (*Salmonella*) compared to Gram-positive [26–29].

the most prevalent infecting organism in MAAs [23, 27, 28, 30].

the most common pathogen, reported in up to 28–71% of cases [21, 23]. Reports from North America and Europe have described Gram-positive Staphylococcus as the most prevalent bacterial responsible for MAAs. On the other hand, there are reported differences regarding infective organisms depending on the geographic area. Many reports from Asia have presented Gram-negative *Salmonella* species as

Depending on the different series, anatomical location, and geographic area, blood cultures have been found to be positive in 50–85% of patients, with organisms being able to be isolated from the aneurysmal tissue in 62–76% of patients [23–26]. Some reviews have related mortality with the type of microorganism involved in aortic infections. In a series of 22 patients who presented with aortic aneurysmal infection, mortality was 36% in those with *Salmonella*-infected aortas, and 82% in those patients with aortic infections due to other microorganisms. Some other series have reported similar findings in terms of lower mortality associated with

Symptoms of mycotic aortic aneurysms are very commonly nonspecific in the initial development of the disease. Patients with MAAs often present with fever of unknown cause. Many series have reported fever as the most common presenting sign of MAAs. These patients with febrile illness frequently present with insidious

A high index of suspicion is of great importance in order to avoid delay in diagnosis, as the natural history of most of these untreated mycotic aortic aneurysms is fatality. The most common causes of death in these patients are lethal sepsis or

A vast majority of patients are symptomatic at the time of diagnosis. Most groups

have outlined rates of MAAs as symptomatic on diagnosis involving 93–100% of cases [28, 31]. One of the most common symptoms at the time of initial evaluation is localized pain. When present, pain is most commonly localized in the abdomen, chest, or back. Some groups have reported pain as the most common initial clinical symptom of MAAs, in up to 88% of patients [28, 32]. It has been previously reported that the classic triad of mycotic aortic aneurysms includes fever, pulsatile mass, and

Other manifestations have been described associated to MAAs, including the

Massive hemorrhage may be a sign of MAAs. Some reports have described aortic

back pain. This triad has been described in around 40% of patients [31].

Although bacteriologic patterns continue to evolve, *Staphylococcus aureus* remains

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

*Aortic Aneurysm and Aortic Dissection*

peripheral mycotic aneurysms of 1–5% [19].

findings, with intracranial arteries being the most common site for mycotic aneurysms (especially the middle cerebral artery), with and incidence of symptomatic

Some other reports have published that the higher incidence sites of infected aneurysms are the abdominal aorta, followed by peripheral arteries (typically occurring at bifurcation sites), cerebral arteries, and visceral arteries, in descending order of frequency [20]. On the other hand, previous historical series have reported that the abdominal aorta was the second most common site of aneurysm infection,

Mycotic aneurysms of coronary arteries are rare, but have also been described. González et al. performed a review including 922 cases of definite infective endocarditis (IE), and reported a 2% rate of symptomatic peripheral mycotic aneurysms. In their review, 66% of mycotic aneurysms were intracranial (in the region of the

With regard to infected aneurysms of the aorta, most reported series have less than 50 patients. Most series concur that the most common aortic location for infected aneurysms of the aorta is the infrarenal aorta, with a similar distribution of

One of the largest series involving MAAs presented 36 cases of aortic infection, with the following epidemiology data: infrarenal aortic aneurysm in 15 patients (42%), a suprarenal aneurysm in 3 (8%), a thoracic aneurysm in 5 (14%), and a

A large multicenter European study was published in 2014, where data from 123 patients with 130 identified MAAs were analyzed. Similar epidemiologic findings were found, with infrarenal location being the most common (51%), followed by descending MAAs (28%), paravisceral (12%), multiple MAAs (6%), and arch MAAs (3%) [23]. Primary MAAs are a challenging and very complex vascular pathology. Although they represent a small proportion of patients within all aortic aneurysms, when left untreated, they almost always develop into rupture or lethal complications. Without

treatment, there is a very high level of lethal complications, including aortic

With regard to bacteriological patterns in infected aortic aneurysms, there have been some changes in bacterial patterns depending on the published series decade. Some initial studies on aortic infection have presented their results confirming *Staphylococcus aureus* as the most common infectious cause, followed by *Salmonella* organisms [24]. A series of 17 patients with MAAs reviewed in 1998 presented *Staphylococcus aureus* as the most common responsible organism (29% of patients),

This change in bacteriologic patterns was already observed in the early 1980s, when comparing those series from before 1965 and those from after 1965. Collected series from English language reported before 1984 (178 patients with 243 MAAs) showed that *S. aureus* was the most common organism (28% of cultures), followed by *Salmonella* (15% of aneurysms) and Streptococcus (10% of patients). This series reported how there was some alteration in the involved bacterial flora before and after 1965. A decrease in the incidence of *Salmonella* infections was seen after 1965 (10% compared with 38% prior to that date), as well as an increase in the incidence

Some current series have presented a much higher incidence of Gram-negative organisms compared with older series, with Gram-negative microorganisms seen in up to 35%

with the common femoral artery being the most common site [21].

middle cerebral artery) and 34% were extracranial [19].

cases between the aortic arch and descending aorta.

thoracoabdominal (TAAA) in 13 (36%) [22].

rupture, abscess formation, and sepsis [17].

followed by *Salmonella* organisms (24% of patients) [25].

of *Staphylococcus aureus* (from 19 to 30%) [21].

**5. Microbiology**

**50**

of cases. Different groups have described a higher incidence of aneurysm rupture and mortality in those patients with Gram-negative infections compared with Gram-positive organisms. Aortic aneurysms with *Salmonella*-related infections have been associated with a faster progression and higher risk of early rupture [23]. Recent series have published an increase in Gram-negative bacteria in MAAs, including *Salmonella*, *E. coli*, *Campylobacter*, *Enterobacter*, *Serratia*, and *Proteus* [23, 26]. Some of these series have reported even higher rates in Gram-negative bacteria (*Salmonella*) compared to Gram-positive [26–29].

Although bacteriologic patterns continue to evolve, *Staphylococcus aureus* remains the most common pathogen, reported in up to 28–71% of cases [21, 23]. Reports from North America and Europe have described Gram-positive Staphylococcus as the most prevalent bacterial responsible for MAAs. On the other hand, there are reported differences regarding infective organisms depending on the geographic area. Many reports from Asia have presented Gram-negative *Salmonella* species as the most prevalent infecting organism in MAAs [23, 27, 28, 30].

Depending on the different series, anatomical location, and geographic area, blood cultures have been found to be positive in 50–85% of patients, with organisms being able to be isolated from the aneurysmal tissue in 62–76% of patients [23–26].

Some reviews have related mortality with the type of microorganism involved in aortic infections. In a series of 22 patients who presented with aortic aneurysmal infection, mortality was 36% in those with *Salmonella*-infected aortas, and 82% in those patients with aortic infections due to other microorganisms. Some other series have reported similar findings in terms of lower mortality associated with *Salmonella*-aortic infections [23, 27–29].
