Teaching Case

A healthy 52-year-old female patient came to the emergency room with severe pain, pallor and coldness of the left lower extremity. Physical examination revealed decreased pulse of the limb. She underwent a computed tomography angiography (CTA) of abdomen, pelvis and lower extremities.

CTA revealed an acute thrombus at the aorto-iliac bifurcation that extended to the common left iliac artery (Fig. 1, 2); also, a splenic abscess (Fig. 3) and a renal infarction zone of the right lower pole (Fig. 4).
In the study of emboli source the presence of a vegetation in the mitral valve secondary to S. Viridans was shown, confirmed by two positive blood cultures, so infectious endocarditis was diagnosed and antibiotics were initiated. Also, a mitral valve replacement was made with a biological prosthetic valve.
Pain in the left lower extremity persisted and intensified a month later, so the patient underwent a new CTA of the abdomen and pelvis. A pseudoaneurysm developed in the left common iliac artery wall (Fig. 5), associated with an ipsilateral psoas muscle abscess (Fig. 6).

Infectious embolism is defined as the transport of an infected bloodstream thrombus in the vascular tree. Infectious embolic events have immediate complications from acute lack of blood flow, as cerebral, myocardial and mesenteric infarcts, and late complications like pseudoaneurysms and abscesses [1, 2].
Embolism can develop in arterial or venous territories, whose sources vary.
The study of arterial emboli source can be categorized into its main causes as cardioembolisms, arterio-arterial embolisms and paradoxical embolisms through communications from right to left circulation.
Septic cardioembolism occurs in the context of infectious endocarditis where vegetations, perforation, infectious disorders of perivalvular tissue, and parietal endocardial enhancement are observed. They can be studied with transthoracic and transoesophagic echocardiography, multidetector computed tomography (MDCT), computed tomography angiography, magnetic resonance image (MRI) and positron emission tomography (PET/CT) [3, 4].
Septic arterio-arterial embolism comprises mainly infectious aortitis over pre-existent atheromatous plaques or aneurysms, and infrequently over medical external devices. The imaging findings are wall thickening, peri-arterial soft tissue density thickening or fluid, and eventually gas. In this case, computed tomography exceeds TEE and TTE accuracy [5, 6].
Arterial mycotic aneurysms can be cause and/or consequence of embolic disease, the most affected segments being the aorta and great peripheral arteries, particularly femoral, cerebral and visceral arteries. They can be generated from septic microemboli to the vasa-vasorum, direct infection by circulating organisms of an intimal tear, contiguous dissemination, and direct injury. They can be studied by Doppler ultrasound, MDCT, CTA and MRI. CTA is the preferred method for most patients, and early findings are similar to those described for aortitis. It characteristically develops a soft tissue mass that can present a ring enhancement with contrast media. The parietal weakness and disruption develops a pseudoaneurysm, which is seen as single—or multiple—saccular dilations, corresponding to blood contained by adventitia or adjacent tissues, and carrying a high risk of rupture. Intraluminal thrombi are not frequent [7].
Venous embolic sources must be mentioned as source of paradoxical arterial embolism through right to left shortcuts or as bacteraemia that previously invaded sick or prosthetic valves. Its causes are infectious endocarditis of the right heart, infected venous catheters and vascular prosthetic devices, demonstrated by vegetations associated with valve apparatus or prosthetic valves. Periodontal or peritonsillar infections, septic thrombophlebitis from extremities or visceral venous territories could also be sources of emboli, and according to medical history, they should be studied with the same imaging modalities [1, 8, 9].