Hospital Medicine

Mycotic aneurysm

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I. What every physician needs to know.

A mycotic aneurysm is a dilation of an artery due to damage of the vessel wall by an infection. It is also referred to as infected aneurysm. The term "mycotic" referring to fungal is a misnomer as various organisms including predominantly bacterial can cause the aneurysm. It is a rare condition that is life-threatening. Delayed treatment can evolve to sepsis, spontaneous arterial rupture with significant bleeding and death. A mycotic aneurysm can develop from (a) contiguous spread from an adjacent infection, (b) septic emboli, (c) hematogenous seeding at sites of endothelial injury, flow turbulence or existing aneurysm or (d) vascular trauma resulting in direct infectious invasion.

II. Diagnostic Confirmation: Are you sure your patient has Mycotic Aneurysm?

A. History Part I: Pattern Recognition:

The symptoms and signs of mycotic aneurysms are diverse and can manifest as symptoms of occult infection which include fever, nausea, weakness, weight loss and fatigue. The symptoms can also be localized to the involved artery. The classic triad of aortitis from mycotic aneurysm includes fever, abdominal pain and pulsatile abdominal mass. Mycotic aneurysm of the aorta can also present as lubosacral pain as they expand. Patients may present with life-threatening bleeding as a result of rupture or gastrointestinal bleeding from aortoenteric fistula.

Mycotic thoracic aorta aneurysm can cause chest and interscapular pain.

Infected aneurysm involving the illiac arteries can produce symptoms of buttock or back pain radiating to the thigh.

Infected cerebral aneurysms can cause headache, seizures, or focal neurologic symptoms; however, many are asymptomatic until aneurysm rupture occurs.

Infected peripheral artery aneurysms may present as pain, a palpable thrill, a pulsatile mass, local inflammatory changes arising from cellulitus or abscess. It can also manifest as compressive neuropathy or vascular compromise from distal embolization or formation of a-v fistula.

B. History Part 2: Prevalence:

The thoracic and abdominal aorta, peripheral arteries, intracranial arteries, and abdominal visceral arteries are involved in descending order. Mycotic aneurysm of the aorta accounts for 0.7% to 1.3% of all surgically treated aneurysms and its incidence in the aortic arch is less frequent. The prevalence of infected cerebral aneurysms is 0.7%-4% of all patients with cerebral aneurysms. The most frequently involved peripheral artery is the femoral artery and the most frequently involved visceral artery is the superior mesenteric artery.

Percutaneous catherization and Intravenous Drug use have accounted for an increase in incidence involving the brachial and femoral arteries.

Predisposing risk factors include: Intravenous Drug use, iatrogenic aortic trauma, bacteremia, infective endocarditis, valvular deformities, immunosuppression, prosthetic arterial devices such as stents or grafts, existing atherosclerotic plaque or native aneurysm and in the elderly, Salmonella septicemia.

C. History Part 3: Competing diagnoses that can mimic Mycotic Aneurysm.

D. Physical Examination Findings.

A mycotic aneurysm should be suspected in any patient with an infected or inflammatory mass continguous to a major vessel.

An infected aneurysm should be suspected when a patient with bacterial endocarditis has neurologic signs and symptoms especially when on antibiotics.

E. What diagnostic tests should be performed?

1. What laboratory studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

Lab tests that will confirm the diagnosis of mycotic aneurysm are positive blood cultures (bacterial + fungal) in conjuction with imaging tests and physical exam that suspect the diagnosis. A negative blood culture does not rule out mycotic aneurysm!

Additional lab tests that are helpful are:

a) Complete blood count - will assist with diagnosing anemia or acute blood loss in the case of possible rupture. It can identify increasing wbc count signifying infection.

b) Basic metabolic panel.

c) PT/PTT/INR

d) Tissue culture and pathology - when surgery is necessitated.

e) Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) - can be elevated in the context of infected aneurysm.

The organisms identified in mycotic aneurysms depend on the source of infection and the location of the affected artery.

In mycotic aneurysms resulting from septic emboli due to infective endocarditis, staphylococcus, streptococcus and enterococcus are common species.

Infected aneurysm due to Methicillin Resistant Staph Aureus (MRSA) is common in intravenous drug users.

Salmonella is the most common organism associated with infected aortic aneurysms. Other organisms found in aortic lesions include Treponema Pallidum and Mycobacterium Tuberculosis.

Fungi such as Candida albicans are rare causes of infected aneurysms.

2. What imaging studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

Useful imaging studies to establish diagnosis and identify associated complications are:

a) Ultrasonography:

  • – Helpful for rapid evaluation in hemodynamically unstable patients in whom AAA rupture is suspected.

  • – Intestinal gas and dilation can limit its accuracy.

  • – Useful for periodic evaluation of aneurysmal size and dimensions.

b) Computed tomography (CT) with contrast:

  • – Noninvasive, accurate test delineating the size and location.

c) CT Angiography/ Magnetic Resonance Angiography (MRA):

  • – Very precise evaluation of aneurysm size and anatomy.

  • – Not feasible if acute rupture is suspected.

  • – If thrombi fill the aneurysmal wall, CTA may underestimate the luminal size.

  • – Can pose a nephrotoxic risk in patients with underlying renal dysfunction.

  • – Can facilitate the diagnosis and planning of surgical intervention.

d) Aortography:

  • – Considered to be the definitive diagnostic procedure.

  • – Can facilitate the diagnosis and planning of surgical intervention.

  • – Preferable if renal artery or aortoilliac disease is suspected or endovascular stent- grafts is considered for treatment.

  • – Carries a small risk of bleeding from site, atheroembolism, allergies and nephrotoxicity.

F. Over-utilized or “wasted” diagnostic tests associated with this diagnosis.

III. Default Management.

A. Immediate management.

In the case of a hemodynamically stable patient in whom mycotic aneurysm is suspected from History and Physical, blood cultures (bacterial + fungal) should be obtained and parenteral antibiotics should be initiated.

The choice of therapy will be determined by the type of organism suspected in the involved site. Once the culture and sensitivity of the organism is confirmed, the antibiotic regimen should be tailored to the infectious agent.

Diagnostic testing should be ordered early (see diagnostic modalities).

Radiographic features suggestive of mycotic aneuyrsm should prompt an urgent vascular surgeon consultation.

In the hemodynamically unstable patient, immediate resuscitation efforts to establish airway, breathing and circulation should be initiated and an immediate sonogram or CT WITHOUT contrast, in case abdominal aorta infected aneurysm is suspected, can provide a rapid assessment of the lesion. Urgent Vascular surgery and/or Thoracic surgery consultation should be called. Once the lesion is suspected, any indication of rupture should prompt immediate surgical intervention.

Surgery is determined by the location of the infected aneurysm and associated complications, the patient's medical condition and immunologic state. The goal is excision of the mycotic aneurysm and re-establishing distal arterial flow. Surgical options consist of extraanatomic or in situ reconstruction together with long-term antibiotics.

Arterial Ligation alone is rarely indicated except for specific instances, generally involving the upper extremities.

Ligation and excision of all infected tissue (including arterial tissue) with bypass grafting to re-establish distal circulation is the general standard. Bypass can be in-situ or extraanatomic through a clean, non-infected plane.

In-situ simply means putting the repair in the anatomical position (in this case, in the infected bed). In situ repairs are the procedure of choice for suprarenal infected aortic aneurysms, carotid aneurysms, or anywhere else where one cannot physically go outside of the anatomic position. An extra-anatomic repair restores flow while keeping the bypass outside the infected area. An example would be an axillary-bifemoral bypass to maintain flow to the legs before ligating and resecting an infected infrarenal aortic aneurysm. It is preferable to perform the bypass prior to ligation to avoid prolonged distal ischemic time.

Endovascular aneurysm repair may be considered as a bridge to open surgical repair but data is limited.

B. Physical Examination Tips to Guide Management.

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C. Laboratory Tests to Monitor Response To, and Adjustments in, Management.

CBC at least every other day to assess resolving leukocytoisis as a response to antibiotic therapy.

Repeat Blood cultures to evaluate for eradication of the identified organism.

In patients who underwent surgical repair of a ruptured aneurysm, a daily CBC during the first few days will also assess the hemoglobin levels.

D. Long-term management.

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E. Common Pitfalls and Side-Effects of Management.

IV. Management with Co-Morbidities.

A. Renal Insufficiency.

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B. Liver Insufficiency.

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C. Systolic and Diastolic Heart Failure.

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D. Coronary Artery Disease or Peripheral Vascular Disease.

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E. Diabetes or other Endocrine issues.

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F. Malignancy.

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G. Immunosuppression (HIV, chronic steroids, etc).

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H. Primary Lung Disease (COPD, Asthma, ILD).

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I. Gastrointestinal or Nutrition Issues.

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J. Hematologic or Coagulation Issues.

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K. Dementia or Psychiatric Illness/Treatment.

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V. Transitions of Care.

A. Sign-out considerations While Hospitalized.

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B. Anticipated Length of Stay.

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C. When is the Patient Ready for Discharge.

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D. Arranging for Clinic Follow-up.

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1. When should clinic follow up be arranged and with whom.

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2. What tests should be conducted prior to discharge to enable best clinic first visit.

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3. What tests should be ordered as an outpatient prior to, or on the day of, the clinic visit.

E. Placement Considerations.

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F. Prognosis and Patient Counseling.

Mycotic aneurysm are rare but life-threatening. Infected aortic aneurysms have a high rate of rupture if not treated promptly. Despite improvements in diagnostic imaging, medical management and surgical options, mycotic aneurysms still possess a high morbidity and mortality. Approximately 7-24% of infected aortic aneurysms showed rupture at presentation and 45-60% revealed impending rupture. Freely ruptured infected aortic aneurysms have a mortality rate ranging from 63-100%. Ruptured infected intracranial aneurysms have a 60-90% mortality. Infected peripheral aneurysms have a 0-15% mortality.

The prognosis of peripheral aneurysms is better as a result of earlier clinical manifestation resulting from their superficial locations. The best chance for optimal outcomes depends on a high clinical awareness leading to early diagnosis and timely surgical intervention with antibiotic therapy.

VI. Patient Safety and Quality Measures.

A. Core Indicator Standards and Documentation.

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B. Appropriate Prophylaxis and Other Measures to Prevent Readmission.

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VII. What's the evidence?

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