[2 children with stridor and a thymus in the posterior mediastinum].

Two infants are described with an inspiratory and expiratory stridor with apnea. X-ray examination showed a mass in the posterior mediastinum. For this reason both infants underwent a diagnostic thoracotomy because detailed study didn't resolve the problem. An aberrant localized thymus was found in both infants. In both infants, however, the complaints persisted after the operation. Both infants needed a second operation to relieve the stridor, which appeared to be due to (primary and secondary) tracheomalacia. This article describes shortly the embryology of the abnormally located thymus. The possibilities to diagnose a posterior mediastinal mass without thoracotomy are also described. Using magnetic resonance imaging (MRI), the posterior located thymus can be diagnosed noninvasively in most cases. The aberrantly positioned thymus should be included in the differential diagnosis of a posterior mediastinal mass, otherwise invasive methods are needed to come to the good diagnosis.