Imaging description

Soft tissue thickening in the periaortic region due to inflammatory aortic aneurysm is well visualized with cross-sectional imaging. CT demonstrates a low-attenuation soft tissue mass representing the fibrotic plaque surrounding a calcified aortic wall. The soft tissue is most prominent anterior and laterally and demonstrates mild enhancement after contrast administration, which has high sensitivity and almost 100% specificity for this diagnosis (Figure 64.1.A). The soft tissue thickening appears slightly T2 hyperintense on MRI indicative of active inflammation. Ultrasound has lower accuracy in diagnosing inflammatory aneurysms and demonstrates the soft tissue thickening as a hypoechoic area surrounding the aorta. Involvement of adjacent retroperitoneal structures including the psoas muscles and medial displacement of the ureters may also occur (Figures 64.1.B and 64.1.C).

Importance

Inflammatory aneurysms of the aorta constitute 3–10% of aortic aneurysms and mostly occur in men. The etiology may be due to chronic inflammation, slow leakage of blood cells or an autoallergic reaction. Although mostly contained, rupture may occur with a higher operative mortality than an ordinary aneurysm. Additionally, due to the frequent extension of inflammation to the ureters leading to hydronephrosis and subsequent renal failure, operative management remains optimum treatment. Endovascular treatments have demonstrated decreased mortality rates; however, problems with residual hydronephrosis remain in a significant number of patients.

Typical clinical scenario

Symptoms of abdominal or back pain, fatigue, and weight loss with an elevated sedimentation rate in a patient with a history of an abdominal aortic aneurysm is highly suggestive of an inflammatory aneurysm.

Differential diagnosis

Soft tissue thickening in other infectious and non-infectious causes of aortitis as well as in idiopathic retroperitoneal fibrosis may occur in the absence of an aortic aneurysm (Figures 64.2A, 64.2B and 64.2C). Similar to inflammatory aneurysm, retroperitoneal fibrosis can result in medial displacement of the ureters (Figure 64.2C). Lymphadenopathy due to lymphoma or metastatic disease is usually differentiated by the presence of discrete nodal masses, elevation of the aorta from the spine, and the lateral displacement of the ureters (Figure 64.3).