AJR 2005; 185:463-465
© American Roentgen Ray Society
Mycotic Aortic Aneurysm Presenting Initially as an Aortic Intramural Air Pocket
Chung-Yi Yang1,
Kao-Lang Liu,
Chung-Wei Lee,
Yuk-Ming Tsang and
Shyh-Jye Chen
1 All authors: Department of Medical Imaging, National Taiwan University
Hospital, College of Medicine, National Taiwan University, No. 7, Chung San S.
Rd., Taipei 100, Taiwan, ROC.
Received July 22, 2004;
accepted after revision September 15, 2004.
Address correspondence to K.-L. Liu
(wgl{at}ntumc.org).
Introduction
Mycotic aortic aneurysm is a common complication of the hematogenous spread
of bacterial infection [1].
Early detection of a mycotic aortic aneurysm is essential for a rapid and
efficacious initial treatment and, therefore, for an improved prognosis. This
case shows that an intraaortic air pocket can be an early radiologic hallmark
of a mycotic aneurysm.
Case Report
Our patient is a 76-year-old man who had a history of diabetes mellitus and
hypertension for more than 10 years before hospitalization in the case in
question. The patient had undergone coronary artery bypass graft surgery for
coronary artery disease 9 years earlier, and peripheral arterial occlusive
disease necessitated amputation of the right foot and femoral artery bypass
surgery 3 years ago.
The patient visited our emergency department because of a sudden onset of
fever and chills. Laboratory analysis of a blood sample did not reveal
leukocytosis but did detect Salmonella. A complaint of slight
abdominal pain prompted a CT examination (LightSpeed 16, GE Healthcare).
Contrast-enhanced CT was not performed because of renal insufficiency. The
unenhanced MDCT scans showed focal fusiform dilatation of the lower abdominal
aorta at the level of the inferior mesentery artery. The surrounding fat
planes were clear. Atherosclerosis-related focal abdominal aneurysm was
considered. In addition, a small air pocket was identified on the left side of
the abdominal aortic wall at the renal level; the air pocket was surrounded by
mild fatty infiltrations (Fig.
1A). A mycotic aneurysm was considered at this area. The mycotic
and the fusiform aneurysms could be seen concurrently on the sagittal
reformatted image (Fig.
1B).
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Fig. 1A —76-year-old man who presented with fever; blood culture
findings revealed Salmonella. Axial abdominal CT scan obtained
without contrast medium shows air pocket in media of aortic wall on left side
at renal level. Line of intima can be outlined by hypoattenuated aortic media
due to edematous change. Minimal fatty strands are also noted around
aorta.
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Fig. 1B —76-year-old man who presented with fever; blood culture
findings revealed Salmonella. Oblique sagittal reconstruction shows
air pocket in aortic wall. Focal aneurysmal dilatation of abdominal aorta is
also found at lower level with clear fat planes.
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After the patient had received antibiotics for 8 days, follow-up MRI
(Magnetom Sonata, Siemens Medical Solutions) showed a focal lobulated saccular
aneurysm arising from the area where the air pocket had been—that is, on
the left side of the aortic wall at the renal level with increased areas of
periaortic fatty stranding (Fig.
1C). There was no definite interval change or dirty fat planes
around the lower abdominal aortic aneurysm.
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Fig. 1C —76-year-old man who presented with fever; blood culture
findings revealed Salmonella. MR image obtained 8 days after CT scan
(A) shows typical mycotic aneurysm on left abdominal aorta at level of
previous location of air pocket.
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The patient's condition improved as a result of the medical treatment.
Follow-up MRI conducted 2 weeks after the initial MRI examination (3 weeks
after initial presentation) showed the partial mural thrombus in the mycotic
aneurysm had not changed in size since the initial CT examination. The
periaortic infiltrations were significantly improved with adjacent clear fat
planes. The patient's condition stabilized with no relapse of fever.
Therefore, he was discharged and was followed up on an outpatient basis.
Discussion
Atherosclerosis is considered to be a cause of weakening in the arterial
wall that results in abdominal aortic aneurysm. Atherosclerosis is a
multifactorial process that is influenced by hypercholesterolemia and modified
lipids, lipoproteins, homocysteine, and infection
[2]. Abdominal aortic aneurysm
is also a familial disorder, being possibly genetic or polygenic in origin
[3].
Transient bacteremia leading to hematogenous infection of atherosclerotic
vessels is the most common cause of mycotic aneurysm. In patients with
salmonellosis cultured from sputum, blood, or urine without an adequate
explanation of the bacterium's origin, intravascular infection must be
suspected [4]. The incidence of
aortic infection in patients with nontyphoid Salmonella bacteremia is
high in Taiwan [5]. Timely
surgical intervention and prolonged IV antibiotic therapy have resulted in
excellent outcomes.
CT features of mycotic aneurysm of the aorta include a hazy aortic wall
with rupture, gas-forming inflammation around the aneurysm, retroperitoneal
paraaortic fluid collection and vertebral erosion, and thrombus formation
within a false lumen after aneurysmal rupture
[4]. In our patient, the
presence of Salmonella in blood cultures and the complaint of slight
abdominal pain prompted an examination using unenhanced CT. This examination
identified an air pocket in the aortic wall. Mycotic aneurysm was suspected.
The follow-up MRI examination revealed the typical mycotic aneurysm at the
level where the air pocket had been identified. The patient's clinical
condition was stabilized with antibiotic therapy.
Gas formation in inflammatory processes including mycotic aortic aneurysm
is not rare [4,
6,
7]. However, the diagnosis of
mycotic aortic aneurysm as the presence of an intramural air pocket before the
formation of a pseudoaneurysm is, to our knowledge, seldom reported in the
literature [7]. Our case
illustrates the possibility of intraaortic gas collecting in a newly formed
mycotic aneurysm and further suggests that detection of an intraaortic air
pocket in the aortic wall should lead to suspicion of an inflammatory process
and the impending formation of a mycotic pseudoaneurysm. Additional studies
should be performed to investigate the development and progression of mycotic
aortic aneurysm.
References
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