Retropharyngeal Ectopic Thymus in a Pediatric Patient With 22q11.2 Deletion Syndrome.

The thymus gland plays a crucial role in the maturation process of lymphocyte T cells. Developmental disorders of this organ might be caused by genetic diseases, such as the 22q11.2 deletion and DiGeorge syndrome. Other manifestations of this condition are heart defects, a reduced number of T cells, hypocalcemia, and facial dysmorphia. A 13-year-old boy with 22q11 deletion syndrome presented with paresis and paresthesia of the right upper extremity. Magnetic resonance imaging (MRI) revealed a solid mass in the retropharyngeal and prevertebral areas. The lesion was excised and, upon histopathological examination, turned out to be ectopic thymic tissue. A follow-up examination showed no recurrence of the lesion. The ectopic thymus is a rare pathology, especially in 22q11 deletion syndrome patients. In general, thymic tissue can be found anywhere along its normal path of descent. In this case, however, its location cannot be explained solely by its embryological origin, as at no point should the thymus or its histological predecessor be located in the retropharyngeal area. As such, this finding challenges our current understanding of thymic embryological genesis.