Early non-aneurysmal infectious aortitis: Cross-sectional imaging diagnosis.

In patients without history of vascular surgery, infectious aortitis is a very uncommon, life-threatening condition with nonspecific clinical manifestations, which exposes the patient to uncontrolled sepsis and to the risk of retroperitoneal rupture. State-of-the-art cross-sectional imaging with contrast-enhanced multidetector computed tomography and magnetic resonance imaging allows confident diagnosis and characterization of unsuspected aortitis in septic patients at an early stage before the development of aneurysmal dilatation. The asymmetric distribution of periaortic inflammatory tissue is helpful for the differentiation of this exceptional disorder from other periaortic abnormalities such as retroperitoneal fibrosis or lymphoma.

DISCUSSION

An elderly, 79-years-old man with history of chronic, stable ischemic congestive heart failure (Class II according to the New York Heart Association, 35% ejection fraction) and atrial fibrillation was hospitalized with persistent fever (up to 38.5°C), progressive appetite and weight loss, vague abdominal and lumbar pain since three weeks. One month earlier, he had a percutaneous interventional procedure including double coronary artery stenting.

At physical examination, he was found dyspneic and tachypneic, with stable hemodynamic parameters. Clinically, no signs of acute worsening of cardiac function were appreciated. Arterial blood gas analysis remained within normal limits during oxygen administration through nasal mask. His abdomen was diffusely tender at palpation without peritonism. Supine chest radiograph (not shown) disclosed basal lung hypoventilation. Urgent laboratory tests disclosed abnormal acute phase markers including 12.780/mmc neutrophils, 62 mg/l C-reactive protein.

Dorso-lumbar radiographs [Figure 1a] and magnetic resonance imaging (MRI) [Figure 1b] did not disclose spinal changes consistent with clinical suspicion of spondylodiscitis. Severe mural calcifications were noted in the abdominal aorta.

Figure 1

Plain radiographs (a) and MRI (b) excluded spinal infections. Unenhanced CT (c) showed normal-caliber aorta with mural calcifications, surrounded by sub-circumferential soft-tissue density (arrowhead). Post-contrast CT (d) showed patent aortic lumen, eccentric periaortic tissue with peripheral enhancement (arrow), distally reaching the bifurcation as seen on CT-angiographic reformations (e and f). T1 (g) and T2-weighted (h) MRI follow-up showed increasing thickness of mixed T1- and T2-hyperintense periaortic tissue (arrowheads), persistently sparing the posterior aspect of the vessel

Thoracoabdominal computed tomography (CT) was requested to investigate possible acute aortic abnormalities, because of progressively worsening pain radiating to the back. Unenhanced [Figure 1c] scans depicted a normal-caliber, heavily calcified atheromatous abdominal aorta partially surrounded by a confluent soft-tissue periaortic density with peripheral enhancement on CT-angiographic [Figure 1d-f] images, raising suspicion of aortitis. Meanwhile, positive hemocultures revealed systemic infection caused by methicillin-sensitive Staphylococcus aureus.

Vascular surgery was deemed contraindicated by the patient's poor conditions and cardiopulmonary function. During intensive antibiotic treatment, with worsening renal function unenhanced MRI [Figures 1g and h] showed progressively increasing, eccentric periaortic inflammatory collection sparing the posterior aspect. After hospital discharge in critical conditions, the patient was lost to follow-up. Then, his clinical conditions slowly improved. Seven months later, during hospitalization because of unrelated reasons, repeated CT-angiography [Figure 2a-c] showed post-treatment reduction of the periaortic tissue, and appearance of a focal luminal dilatation of the infrarenal aorta that was attributed to postinflammatory damage to the arterial wall.

Figure 2

(a-c): Contrast-enhanced CT obtained seven months later show reduction of treated inflammatory periaortic tissue (arrowheads), and appearance of a focal luminal dilatation of the infrarenal aorta (arrows). Note L1 vertebral body fracture following fall in B

Aortitis is a broad term that includes a spectrum of different disorders characterized by inflammatory changes of one or more layers of the aortic wall, regardless of the underlying mechanism. In most cases, aortitis is non-infectious in origin, such as with Takayasu or giant-cell arteritis.[12]

Conversely, infectious aortitis is a very rare, life-threatening disease that exposes the patient to uncontrolled sepsis and aortic rupture, and conveys a poor prognosis if unrecognized. Pathologically, aortic infection is defined by bacterial contamination of the arterial wall, most usually resulting from hematogenous dissemination, or uncommonly from secondary invasion of the aorta by adjacent spondylodiscitis. The most common causative organisms include Staphylococcus aureus, Salmonella, Escherichia coli, and Pseudomonas.[134] Infectious aortitis typically affects elderly and/or immunocompromised people with high-grade bacteremia, such as those with endocarditis, septic embolism, or intravenous drug abuse. Most usually, infection is associated with pre-existing aneurismal dilatation, although in some cases it can occur in a normal-caliber vessel in association with other abnormalities such as severe atherosclerotic disease, cystic medial necrosis, diabetes, medical devices or surgery.[14-6]

Clinical manifestations are vague and nonspecific, including fever, variable pain in the chest, back or abdomen, malaise, and elevated biochemistry acute phase reactants. In patients with prolonged signs and symptoms of systemic infection, a high clinical suspicion index is required not to miss the diagnosis. Probably underdiagnosed, aortic infection is in most cases unsuspectedly detected at imaging.[15] Establishing the diagnosis is challenging but is essential in preventing the devastating complications such as uncontrolled sepsis and rupture. Intensive, prolonged antibiotic treatment plus complete surgical removal of infected tissue, aneurysm repair, and restoration of distal blood flow are crucial for survival.[4-6]

Universally available and extremely fast, multidetector CT is almost invariably the preferred modality to investigate acute aortic conditions. However, uncommonly, aortic inflammatory changes can be identified at cross-sectional imaging in an early stage before luminal dilatation. CT signs include periaortic increased fat density or hypoattenuating, variably enhancing soft-tissue aortic wall thickening, whereas presence of air in the vessel wall is characteristic yet exceptional. The differential diagnosis of this early-stage appearance includes retroperitoneal fibrosis, periaortic hemorrhage from contained bleeding, syphilitic or tuberculous aortitis, lymphomatous tissue, or adenopathies. A useful sign is the asymmetrical distribution of periaortic abnormalities, which typically spare the posterior aspect of the aorta.[1245] In a later stage, the infected aorta undergoes a rapid luminal enlargement or the development of a saccular pseudo-aneurysmal dilatation, with characteristically absent mural calcifications. Further complications that are detectable at CT imaging include obstructive hydronephrosis, distant or iliopsoas abscess formation, aortoenteric fistulization, and retroperitoneal rupture.[2-4] Although its imaging appearances have been very scarcely reported, MRI may help to characterize mural or endoluminal abnormalities of the aorta, by demonstration periaortic inflammation and/or adventitial fibrosis with better contrast resolution. Increased uptake in the inflamed periaortic tissue may be even demonstrated by Positron Emission Tomography.[1]

As this case demonstrates, cross-sectional imaging provides early detection, confident characterization, and follow-up of unsuspected aortic infection in septic patients.