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Mycotic Aneurysms

posted Jul 11, 2013, 8:44 PM by Eliany Mejia   [ updated Jul 12, 2013, 6:20 AM by Purnema Madahar ]

This week we had very interesting cases and I wanted to discuss about one of them, thanks to Dr. Sabari for presenting this case and to Dr. Garcia for sharing his insights and expertise with us. This is an unfortunate 64 year old female with past medical history of HIV on HAART and HTN presenting with fevers and low back pain, found to have L5 spinal osteomyelitis and aortic inflammation. Subsequent work up reveals MV vegetation with perforation and mobile mass and psedudoaneurysm in the aortic arch, likely secondary to subacute endocarditis with intravascular complications. (If you haven’t seen these imaging, I strongly recommend you to do it!). So, I'd thought I'd take this opportunity to talk about mycotic aneurysms.

·         What is a mycotic aneurysm? What are the most common pathogens?

·         What are the clinical manifestations?

·         What are the imaging modalities used for assessment of infected aneurysms? What are the imaging features of infected aneurysms?

·         What are the treatment options for infected aneurysms? What is the prognosis?

 

What is a mycotic aneurysm? 

A mycotic aneurysm is an aneurysmal degeneration of the arterial wall as result of an infection which may be due to bacteremia or septic embolization from infective endocarditis as in the case presented.  This can result in sepsis, or life threatening bleeding if the aneurysm ruptures. Infected aneurysms are uncommon and less than 3% of abdominal aortic aneurysms are mycotic aneurysms. The aorta, peripheral arteries, cerebral arteries, and visceral arteries are commonly involved. 


The term "mycotic aneurysm" was first used by Osler in 1885 to describe a mushroom-shaped aneurysm in a pt with subacute bacterial endocarditis (the orginal article is attached!). This term may create considerable confusion, since "mycotic" is typically used to define fungal infections. However, the majority of mycotic aneurysms are caused by bacteria. Although some authors use the term “mycotic” to describe infected aneurysm regardless of etiology, the use of this term should be limited to those aneurysms that develop when material originating in the heart causes arterial wall infection and subsequently dilation.


What are the most common pathogens? Pathophysiology?

Currently, about 80% of mycotic aneurysms are the result of microbial aortitis; 3% are estimated to involve infection of a preexisting aneurysm. Staphylococcus and Streptococcus species are the most common causes of infected aneurysms. Staphylococcus aureus (30%), especially MRSA in IVDU, and Salmonella species (50%) are the predominant organisms in the postantibiotic era, with S aureus also being the major organism seen in vertebral osteomyelitis.

Our patient had S. pneumo Ag (+) however, S pneumoniae is not commonly associated with mycotic aneurysms and is very rarely reported as a cause of vertebral osteomyelitis.(I was able to find only few cases report) 

Gram-negative bacteria, such as E. Coli, Klebsiella, and Pseudomonas, are uncommon causes of infected aneurysms that are becoming more frequent. Mycobacterium and fungi, such as Candida albicans and Aspergillus, are rare causes of infected aneurysms. Sterile blood cultures occur in 18%–50% of pts with infected aneurysms (similar to our patient). Polymicrobial cultures in patients with infected aneurysms are uncommon but are more frequently found in intravenous drug abusers.

Multiple mechanisms have been postulated:

-       Direct bacterial invasion of the arterial wall with subsequent abscess formation or rupture,

-       Septic or bland embolic occlusion of the vasa vasorum,

-       Immune complex deposition with resultant injury to the arterial wall.

 

What are the clinical manifestations?

Mycotic aneurysms are a serious clinical condition that is associated with significant morbidity and mortality. Symptomatology is frequently nonspecific during the early stages and pts may remain asymptomatic until rupture occurs; consequently, their true incidence in active IE is unknown and a high index of suspicion is required to make the diagnosis.

Symptomatology will depend of the location of the infected aneurysm, for example mycotic thoracic aortic aneurysms usually manifest as chest and interscapular pain, whereas infected abdominal aortic aneurysms usually manifest as abdominal pain with or without a pulsatile mass. Infected peripheral aneurysms may manifest as pain, a pulsatile mass, a palpable thrill, local inflammatory changes (cellulitis or abscess), vascular compromise (distal embolization, thrombophlebitis, or AV fistula), or compressive neuropathy. Infected cerebral aneurysms can cause headache, seizures, or focal neurologic symptoms.

In general, infected aneurysms have a poor natural history,  7% to 24% of infected aortic aneurysms demonstrate free rupture and a 47%–61% demonstrate contained or impending rupture at presentation. Freely ruptured infected aortic aneurysms have 63%–100% mortality.

Early diagnosis is the cornerstone of effective treatment. Without medical or surgical management, catastrophic hemorrhage or uncontrolled sepsis may occur.

What are the imaging modalities used for assessment of infected aneurysms? What are the imaging features of infected aneurysms?

Imaging modalities, such as multidetector CT and MRI, have replaced conventional angiography as minimally invasive techniques for detection of infected aneurysms in clinically suspected cases.

Doppler US allows noninvasive assessment for infected aneurysms in the peripheral arteries.

Imaging features of infected aneurysms include a lobulated vascular mass, an indistinct irregular arterial wall, perianeurysmal edema, and a perianeurysmal soft-tissue mass. 

What are the treatment options for infected aneurysms?

The management of mycotic aneurysms requires eradication of the source of infection and maintenance of distal arterial flow. Treatment consists of antibiotic therapy combined with aggressive surgical debridement of the infected tissue and vascular reconstruction, as needed. Endovascular therapies may have a role in the treatment of ruptured infected aneurysm and the treatment of patients at prohibitive risk for open surgery.

Antibiotics should be continued postoperatively for a minimum of 6 to 8 weeks. In some cases, depending on the method of arterial reconstruction, oral antibiotics may be required for a lifetimeThe key to a successful outcome in this uncommon but difficult to manage entity is early diagnosis and aggressive treatment. Our patient is not a good surgical candidate and is currently on antibiotics (hoping for the best) and will have follow up with imaging to monitor response and to access the need for intervention.

Attached are: the original aricle published by Osler in BMJ in 1885 (a piece of history), a review article about mycotic aneurysms, clinical presentation and diagnostic modalities, as well as the 2011 Appropriate Use Criteria for Echocardiography, which addresses the appropriate use of TTE, TEE, and stress echocardiography. Thanks Dr. Garcia for the reference!

 Have a good weekend!

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Purnema Madahar,
Jul 11, 2013, 8:44 PM
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Purnema Madahar,
Jul 12, 2013, 6:00 AM
Ċ
Purnema Madahar,
Jul 12, 2013, 6:00 AM
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