Mycotic (Infected) Aneurysm Caused by Streptococcus pneumoniae

Khosrow Afsari, MD, Touro University College of Osteopathic Medicine, Vallejo, Calif; Robert Stallone, MD, Doctor's Medical Center, San Pablo, Calif; Glenn D. Wong, Touro University College of Osteopathic Medicine, Vallejo, Calif.

Disclosures

Infect Med. 2001;18(6) 

In This Article

Discussion

In a review of more than 20,000 autopsies performed at Boston City Hospital from 1902 to 1951, aortic aneurysms were found in only 1.5%, with mycotic aneurysms, in turn, accounting for only 2.6% of these cases.[1] However, an increasing number of these aneurysms have occurred in recent years, suggesting that the incidence may be increasing.[3] The most common site of mycotic aneurysms is the femoral artery (38%), followed by the abdominal aorta (31%).[4]

Most infected aortic aneurysms in early reports were associated with valvular cardiac infectious diseases before the antibiotic era.[5] Frequent complications from septic emboli were often fatal. With the introduction of antibiotics, the mortality rate decreased because of effective treatment of bacterial endocarditis. Currently, about 80% of mycotic aneurysms are the result of microbial aortitis (Table); 3% are estimated to involve infection of a preexisting aneurysm.[5]

S pneumoniae is not commonly associated with mycotic aneurysms and is very rarely reported as a cause of vertebral osteomyelitis.[6]Staphylococcus aureus (30%) and Salmonella species (50%) are the predominant organisms in mycotic aneurysms in the postantibiotic era,[3] with S aureus also being the major organism seen in vertebral osteomyelitis.[6]

The diagnosis of mycotic aneurysms can be very difficult. Fever and leukocytosis are usually the first findings in 70% of cases,[5] with a palpable aneurysm or back pain constituting the third part of a classic triad of symptoms. However, several patients have presented with nonspecific abdominal or chest pain and no distinctive clinical features.[5] The symptoms of sepsis may be discrete and may easily go unrecognized, especially in the early stages.

The onset of both mycotic aneurysm and osteomyelitis can be insidious. Pain and fever may be the only presenting symptoms. Untreated osteomyelitis of the spine may extend anteriorly into the soft tissues, as in our patient, or it may extend posteriorly into the vertebral canal and result in a chronic epidural abscess.[7]

Our patient presented atypically, with absence of fever, leukocytosis, or palpable mass. This created a complex clinical picture with CT required for diagnosis. There was no antecedent history that suggested pneumococcal infection. It is unclear where the initial process began. The pneumococcal infection may have started as a mycotic aneurysm of the descending thoracic aorta, eroding posteriorly into the vertebrae and anteriorly toward the lung, or it could have started in the lung, spreading posteriorly to the descending thoracic aorta and eroding the vertebrae. A third possibility is that osteomyelitis of the vertebrae eroded anteriorly to both the descending thoracic aorta and the lung. The primary source of infection is still unknown.

Clinical suspicion is fundamental in the diagnosis of mycotic aneurysms. Prompt treatment increases the likelihood of a favorable outcome. The source of infection should be thoroughly investigated, and if warranted, CT of the chest and abdomen should be done.[3] CT provides earlier diagnosis and is considered the gold standard for diagnosis of this disease.[5] The CT scan may show irregular peripheral enhancement of the aortic wall, consistent with periaortic inflammation and effusion. Angiography provides the anatomic details of the lesion and adjacent vessels but will not show the periaortic extension that CT can demonstrate.

Transesophageal echocardiography may also assist in the early diagnosis of mycotic aneurysms. Because of the close proximity of the esophagus to the aorta, it provides detailed views of the descending aorta. Color Doppler echocardiography can demonstrate the flow from the aorta into the abscess cavity.[4]

The management of mycotic aneurysms requires eradication of the source of infection and maintenance of distal arterial flow. Surgery is almost always indicated, since mortality for untreated patients is greater than 90%.[1] Bactericidal antibiotics should be started immediately once the diagnosis has been made. Start with a broad-spectrum antibiotic covering both gram-positive and gram-negative bacteria until cultures from the aortic tissue and blood have been obtained. Adjustments in antibiotic selection can be made following sensitivity results.

Antibiotics should be continued postoperatively for a minimum of 6 to 8 weeks.[1] In some cases, depending on the method of arterial reconstruction, oral antibiotics may be required for a lifetime.[3]

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