Teaching Case

56 years-old male went to the emergency room complaining of fever for the last 10 days and urinary tract symptoms. Two weeks ago he presented diarrhoea and weight loss, with a positive stool test for Campylobacter Fetus.

Despite antibiotic therapy, the fever persisted. Suspecting a complicated infectious disease a complete radiological evaluation was carried out.

A contrast-enhanced CT was performed (FIG01, FIG02). The most significant finding was aortic atheromatous disease with calcified plaques and a small saccular aneurysm arising in the left side of the infrarenal aorta, measuring 19 x 16 mm, with stranding of the surrounding fat and adjacent reactive nodes. Findings that in this clinical picture should rise the suspicion of a mycotic aneurysm. A retroaortic left renal vein was adjacent to the lesion.

Doppler ultrasound showed a pulsatile saccular lesion in B-mode image (FIG03, FIG04, FIG05), with colour filling and arterial flow in colour mode (VIDEO-03/ FIG06), in the left side of the infrarenal aorta.

In the contrast-enhanced ultrasound (CEUS) (FIG07, FIG08) this lesion is better delimited, and there is contrast enhancement of surrounding tissues suggesting associated inflammatory component.

A PET-TC (FIG09) was performed after endovascular repair and showed a rise in metabolic activity of diffuse and heterogenous distribution on the top third of the abdominal aorta, related to post-surgery changes, with a post-surgical collection in left paraaortic location.

Osler first used the term mycotic aneurysm in 1885 to define any localized dilatation of the arterial tree caused by infection. Mycotic aneurysms are part of the spectrum of infectious aortitis The aorta is normally very resistant to infection; however, an abnormal aortic wall, like that associated with atherosclerotic disease or preexisting aneurysm, the use of medical devices and prostheses, or diabetes disease, makes it more susceptible to infections like S. aureus (1).

Other organisms, although less common but to be considered especially in immunocompromised patients are L. monocytogenes, B. fragilis, C. septicum and M. tuberculous. Campylobacter rods (Enteric Gram-negative), specifically Campylobacter fetus, has been noted to have a predilection for vascular endothelium and immunocompromised patients and seem to have greater virulence in this context with a significantly high incidence of aneurysmal rupture (2, 3, 4).

Mechanisms of infection include hematogenous spread, contiguous seeding from adjacent infection, and traumatic inoculation. Men are affected more often than women, with most cases seen in adults after the 5th decade of life. Mycotic aneurysms are only 0.7 to 2.6% of all aortic aneurysms. Clinical correlation is important in its differential diagnosis. Contrast-enhanced computed tomography is the gold standard for diagnosing and assessing aneurysm, with sensitivity between 92%–96% and specificity between 93%–100%. Imaging manifestations of infectious aortitis include aortic wall thickening with periaortic oedema, rapidly progressing saccular aneurysms or pseudoaneurysm (when are seated on graft anastomotic site). The presence of a soft-tissue cuff and occasionally air in the aortic walls are also common imaging features. The image of the soft tissue cuff, although very sensitive, requires a differential diagnosis with neoplasia, retroperitoneal hematoma or lymphoproliferative processes. The presence of a hypoattenuating concentric rim in the aortic wall helps differentiate from non-infective aneurysms (5, 6).

Peripheral arteries are best imaged initially by ultrasound. Aneurysms appear as circumscribed, hypoechoic lesions adjacent to the main arterial lumen with turbulent flow on Doppler (5).

Disruption of aortic calcification is a late sign, and may herald imminent rupture; in contrast, extravasation indicates this has already occurred. Risk of rupture correlates with aneurysm diameter and rate of enlargement; there are no other imaging features that accurately predict outcome (7).

Prolonged culture-specific antibiotic therapy in combination with conventional surgery or endovascular techniques is advocated as a key component for successful treatment. In general, open surgery involves aneurysmectomy with or without primary reanastomosis. Distal revascularization can be performed with an in situ graft or extraanatomic reconstruction, depending on the location of the infected aneurysm (8).