Radiological Case of the Month

Figure 1. Frontal chest radiograph at age 6 months. A retrocardiac rounded mass is identified and splays the left main stem bronchus.

Figure 2. Computed tomographic scan of the chest at the level of the left atrium. Intravenous contrast enhancement shows that the retrocardiac mass enhances homogeneously and is closely associated with the thoracic aorta.

Figure 3. Magnetic resonance image of the chest (coronal T1-weighted sequence). There is flow void in the lesion that arises from the thoracic aorta with which it communicates via a broad neck. The lesion is a vascular structure with active blood flow.

Thoracic aortic aneurysm is an unusual complication of umbilical artery catheterization.¹ Although umbilical artery catheters have been used since 1961, the first case report of an associated aneurysm was in 1976.² From subsequent case reports, a common identified cause is sepsis, usually S aureus, as in this case.^1-4 The association of sepsis with aneurysm formation suggests seeding of the aortic wall secondary to localized trauma at the tip of the umbilical artery catheter.^1,3,4

The differential diagnosis of the mediastinal mass found on chest radiograph in this child includes neurogenic tumor, esophageal or bronchogenic duplication cyst, or round pneumonia.³ A murmur, best heard at the back, should raise suspicion of an aortic aneurysm. This lesion displaced the left main bronchus, producing the patient's history of raspy breathing when supine. An esophageal duplication cyst was considered, and computed tomography was performed. Magnetic resonance imaging would have been a better initial study to evaluate for intraspinal extent of a neurogenic tumor.

Findings from computed tomographic scan included an aneurysm with contrast enhancement of the lesion contiguous with the lumen of the thoracic aorta. The magnetic resonance study was completed while the child was sedated to better depict the extent and neck of the aneurysm. This patient underwent successful aortic graft repair. Findings from histopathologic examination revealed that the lesion was not a true pseudoaneurysm, but the thinned aortic wall was fibrotic without acute inflammation.

Accepted for publication June 12, 1998.

Corresponding author: Daniel E. Long, MD, The Ohio State University Medical Center, Department of Diagnostic Radiology, 450 W 10th Ave, No. 255, Columbus, OH 43210.