Cough and slight fever developed in a 3-month-old infant. The physical examination gave normal results. A chest roentgenogram was obtained.
Normal chest roentgenogram with normal thymic shadow. Discussion: The chest roentgenogram shows normal bony structures, lung fields, and pleura. The heart is not enlarged, but there is a shadow projecting superiorly and laterally to the right of the heart and mediastinum (Fig 1, top). This shadow has a subtle, wavy lateral margin with indentations exactly opposite the anterior ends of the ribs (Fig 1, bottom). This is the thymic "wave sign," first described by Mulvey,1 which indicates that the shadow in question is the thymus.Intimate contact between the lateral border of normal soft thymic tissue and the anterior ends of the ribs (or their chondral extensions) creates this characteristic roentgenographic appearance. Thymic tumors or other masses in the anterior mediastinum are generally firmer and not positioned
Colley DP. Mediastinal Mass in a Sick Infant. JAMA. 1974;229(9):1217–1218. doi:10.1001/jama.1974.03230470059033
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