Joseph Junewick, MD FACR
over 8 years ago
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Heather Borders, MD
|Diagnostic Category: Developmental or Congenital
|Created: over 3 years ago
|Updated: over 3 years ago
2 year old with (asymptomatic) left sided pharyngeal fullness noted at tonsillectomy.
Retropharyngeal ectopic thymus (not pathologically proven)
CT=Poorly defined ovoid mass in the left retropharynx with mild mass effect on the nasopharynx and adjacent tissue planes.
MRI=Ovoid homogeneous mass in the left retropharynx with similar signal to thymus and also lymphatic tissue. Normal thymic tissue can be seen in the mediastinum (sagittal T2).
Aberrantly located thymic tissue arises as a consequence of migrational defects during embryogenesis. The thymus is derived from the third and, to a lesser extent, fourth pharyngeal pouches. Aberrant thymic tissue results when tissue breaks free from the thymus as it migrates caudally into the mediastinum. Aberrant thymic tissue may be found in any position along a line from the angle of the mandible to the sternal notch, and in the anterior mediastinum to the level of the diaphragm.
In children, the differential diagnosis includes infection, trauma, neoplasm, and congenital abnormalities. Aberrant cervical thymic tissue, although occasionally observed on autopsy examination, is rarely clinically significant.
In this case, other possiblities for the mass were considered, but the imaging features and history of incidental discovery in an asymptomatic patient are most compatible with ectopic thymus. Follow up and/or biopsy is currently pending.
Retropharyngeal Aberrant Thymus. Samir S. Shah, MD
Pediatrics Vol. 108 No. 5 November 1, 2001 pp. e94