Dear Editor,

We read with interest the article “Inspiratory stridor and dysphagia in two newborn infants caused by ectopic thymus tissue” in the September 2009 issue of the European Journal of Pediatrics [1]. This has caused us to remind that “superior herniation of normal mediastinal thymus” or “thymic herniation” is an entity defined as intermittent migration of the normal thymus out of the thorax into the suprasternal region during increased intrathoracic pressure caused by coughing, sneezing, crying, and Valsalva maneuver [2]. As the authors mentioned, surgical removal and histological examination is often the only way to prove the diagnosis of ectopic thymic masses, so to avoid unnecessary biopsy or surgery, it is very important to identify and differentiate thymic herniation from other neck masses especially from ectopic thymic masses because it is only normal thymic tissue and necessary for the maintenence of normal immune function in children. Pediatricians, radiologists, and especially surgeons should be aware of this entity so as not to give harm to the children.