Francisco Nacinovich
Martin E. Stryjewski
Matthew E. Falagas
DESCRIPTION 
- An aneurysm that develops in a vessel as part of an infectious process, such as infective endocarditis. The term "mycotic" refers to the shape of the dilation which resembles a fungus and not to the etiology, which is most commonly bacterial.
- Mycotic aneurysms (MA) are described as intracranial or extracranial (1). The term MA is also commonly used in patients with infections of preexisting aneurysms.
- However, one must acknowledge that there is no consensus regarding the terminology (2). Indeed, terms proposed by Wilson (3) seem the most appropriate: Mycotic aneurysms are endocarditis-related infected aneurysms, infection of existing aneurysms or microbial arteritis are bacteremia-related infected aneurysms, and the last category are posttraumatic infected false aneurysms.
EPIDEMIOLOGY
Incidence
- Around 2–4% of patients with IE develop intracranial MA. The incidence is underestimated because of the asymptomatic cases.
- In studies from the 1970s, up to 15% of patients with IE developed MA.
Prevalence
- Prevalence of MA in the general population is unknown. Most probably it decreased in the post antibiotic era.
- Annual prevalence of MA among injection drug users is 0.03%.
- <1% of aortic aneurysms are MA.
RISK FACTORS
- Infective endocarditis
- Other: Deep infections contiguous to a blood vessel, impaired immunity, arterial trauma, and older age
- Intravenous drug abuse
GENERAL PREVENTION
Early recognition, diagnosis, and prompt initiation of antibiotic therapy in patients with IE.
PATHOPHYSIOLOGY
- Staphylococcus aureus, Salmonella spp. and Treponema pallidum are the organisms with greatest affinity for the arterial wall.
- MAs can occur through different mechanisms:
- Septic emboli from valvular vegetations in IE to the vasa vasorum or the intraluminal space (1)
- Bacteremic seeding on a previous intimal injury (e.g., atherosclerotic plaque)
- Spread of infection through a contiguous foci (e.g., osteomyelitis, deep abscesses).
- Arterial trauma with direct inoculation of microorganisms (e.g., penetrating injury, intravenous drug abuse) or surgery (e.g., percutaneous angiography).
ETIOLOGY
- S. aureus is the most common cause (up to70%), followed by Salmonella spp. (up to 24%); T. pallidum is now rare. Non-typhi Salmonella bacteremia can result in aortitis or MA especially in the elderly with atheromatous lesions.
- MAs associated with Salmonella spp. almost always occur below the renal arteries and usually develop in preexisting vascular lesions (e.g., atherosclerosis plaques).
- Other pathogens: S. viridans, S. pneumoniae, gram-negative bacilli (e.g., Brucella, Pseudomonas, Klebsiella), Mycobacterium tuberculosis, fungi (Candida, Zygomycosis, Cryptococcus, and Aspergillus).
- Take into consideration local epidemiology, that is, in Thailand, Burkholderia pseudomallei is the most frequent pathogen associated with mycotic aneurysms (4).
COMMONLY ASSOCIATED CONDITIONS
- Infective endocarditis. Mycotic aneurysm constitutes a minor criterion according to the modified Duke endocarditis criteria (1)
- Persistent bacteremia in patients with previous arterial lesions
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HISTORY
- MAs are usually asymptomatic unless there is an arterial leak or rupture. Symptoms are dictated by the anatomic region of the vessel.
- Stroke like syndromes with fever, headache, and/or seizures are common in patients with symptomatic intracranial MAs.
- Fever and abdominal or low pain can be seen in patients with MA in the aorta. Secondary infection of preexisting aneurisms is most common in the abdominal aorta.
- In patients with IE, premonitory signs and symptoms can precede the rupture of MA with a median of 6 days (up to 1 month).
PHYSICAL EXAM
- Leak or rupture of intracranial MA (ICMA) can produce meningeal irritation, focal neurologic signs, hemianopsia, and/or coma. Meningeal irritation can be the only finding.
- Intra-abdominal MAs can present with peritoneal signs, back pain, gastrointestinal bleeding, or shock.
DIAGNOSTIC TESTS & INTERPRETATION
Lab
Initial lab tests
- Increased WBCs (65–70%) and anemia (50%) are often present
- Blood cultures are positive in most patients (50–85%)
Follow Up & Special Considerations
Culture of tissue (affected vessel) is positive in approximately 80% of cases
Imaging
Several procedures are available; suspecting the localization of the MA is the key in selecting the initial procedure.
Initial Approach
- Conventional angiography is the gold standard in all cases of MA
- Doppler ultrasound (US) is useful as a first step in extremities or abdominal aorta
- Contrast enhanced CT can detect blood vessel rupture or aneurysmal dilatation in the CNS and in the aorta; normal brain CT scan makes intracranial MA unlikely.
- Transesophageal Doppler US is useful to evaluate heart abnormalities (e.g., valves).
- MRI and also digital subtraction angiography are sensitive for intracranial aneurysms. False–positive results may occur.
Follow Up & Special Considerations
Compromise of multiple vessels could be found in up to 25% of patients.
Diagnostic Procedures/Other
- Radionuclide scintigraphy (e.g., Tc99) may help to differentiate infectious from noninfectious processes; false–positive results occur.
- Although experience is still limited, PET is a promising diagnostic tool in patients with vascular infections.
Pathological Findings
Destruction of the normal arterial wall architecture with acute and chronic inflammation starting from vasa vasorum and progressively compromising the adventitial surface, the adjacent muscular layer, and then the internal elastic membrane allowing dilation and rupture. The intima can be intact. MAs usually occur at branching sites.
DIFFERENTIAL DIAGNOSIS
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MEDICATION
- Most patients with intracranial aneurysms have resolution with antibiotics alone. Parenteral antibiotics should be directed to the isolated microorganism for at least 6–8 weeks (regardless of surgical resection).
- Some experts recommend a longer duration of treatment if biochemical markers (such as white blood cell count, erythrocyte sedimentation rate, and C-reactive protein) do not return to normal values.
- Long-term oral suppressive therapy following parenteral antimicrobials should be considered for difficult to treat microorganisms.
ADDITIONAL TREATMENT
General Measures
According to the clinical status
Issues for Referral
Consult vascular surgery and or neurosurgery according to the affected vessels.
SURGERY/OTHER PROCEDURES
- Surgical treatment depends on the anatomic location and it is usually reserved for those patients with bleeding or enlarging aneurysms despite adequate antibiotic treatment (5).
- Endovascular surgical treatment is a valid alternative to open surgery for the treatment of mycotic aneurysms (6)
- Cryopreserved aortic allografts have also been used for the treatment of mycotic aneurysms of the aorta (7)
IN PATIENT CONSIDERATIONS
Admission Criteria
Clinical signs due to MA (e.g., compression, rupture, and leak) in a patient with risk factors (e.g., IE).
IV Fluids
According to the clinical scenario
Nursing
No specific recommendation.
Discharge Criteria
When clinical status improves, patient is afebrile, and complications have resolved or have been adequately managed. Aneurysm should be stabilized or resolving.
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FOLLOW-UP RECOMMENDATIONS
- Intracranial bleeding due to a ruptured MA usually occurs early in the course of the IE. The first weeks of treatment are critical for follow-up.
- Rupture occurring months or even 2 years after the treatment have been described.
Patient Monitoring
- Patient should be clinically followed with inflammatory markers such as WBC, sedimentation rate, and CRP
- Blood cultures should be obtained (before, during, and after treatment)
- Images (noninvasive procedures or angiogram) should be obtained to ensure the MA is getting smaller (expert opinion)
DIET
Rich in fiber to avoid constipation and excessive Valsalva (expert opinion)
PATIENT EDUCATION
Patients should be aware of fever and symptoms that can be associated with their MA (e.g., headache, vision loss).
PROGNOSIS
The mortality of MA is high and depends on the rupture. In patients with intracranial MA associated with IE, the overall mortality is around 50%; mortality in those who had a ruptured MA is 80%, and in those with intact MA is 30%, respectively.
COMPLICATIONS
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