Retropharyngeal aberrant thymus

Introduction. Upper airway obstruction from a retropharyngeal mass requires urgent evaluation. In children, the differential diagnosis includes infect ion, trauma, neoplasm, and congenital abnormalities. Aberrant cervical thym ic tissue, although occasionally observed on autopsy examination, is rarely clinically significant. We present the case of an infant with respiratory distress attributed to aberrant thymic tissue located in the retropharyngea l space. Case. A 6-week-old infant was brought to the emergency department for evalu ation of stridor associated with periodic episodes of cyanosis. Lateral nec k radiograph revealed widening of the retropharyngeal soft tissues. The pat ient's symptoms did not improve with intravenous ampicillin-sulbactam. Magn etic resonance imaging (MRI) performed on the seventh day of hospitalizatio n revealed a retropharyngeal mass that extended to the carotid space. The m ass was easily resected using an intraoral approach. Microscopic examinatio n demonstrated thymic tissue. A normal thymus was also observed in the ante rior mediastinum on MRI. The patient recovered uneventfully and had no furt her episodes of stridor or cyanosis. Discussion. Aberrant cervical thymic tissue may be cystic or solid. Cystic cervical thymus is more common, and 6% of these patients present with sympt oms of dyspnea or dysphagia. Aberrant solid cervical thymus usually present s as an asymptomatic anterior neck mass. This case is unusual in that solid thymic tissue was located in the retropharynx, a finding not previously re ported in the English literature. Additionally, the patient presented in ac ute respiratory distress, and the diagnosis was confounded by the presence of mild laryngomalacia. In retrospect, our patient likely had symptoms of i ntermittent upper airway obstruction since birth. The acute respiratory dis tress at presentation was likely the result of laryngomalacia exacerbated b y the presence of aberrant thymic tissue and a superimposed viral infection . Aberrantly located thymic tissue arises as a consequence of migrational def ects during thymic embryogenesis. The thymus is a paired organ derived from the third and, to a lesser extent, fourth pharyngeal pouches. After its ap pearance during the sixth week of fetal life, it descends to a final positi on in the anterior mediastinum, adjacent to the parietal pericardium. Aberr ant thymic tissue results when this tissue breaks free from the thymus as i t migrates caudally. Therefore, 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 an autops y study of 3236 children, abnormally positioned thymic tissue was found in 34 cases (1%). The aberrant thymus was most often located near the thyroid gland (n = 19 cases) but was also detected lower in the anterior neck (n = 6 cases), higher in the anterior neck (n = 8 cases), and at the left base o f the skull (n = 1 case). The presence of thymic tissue in the retropharyng eal space in our patient is more unusual given the typical embryologic orig in and descent of the thymus in the anterior neck to the mediastinum. Children with aberrant thymus may have associated anomalies. Twenty-four of 34 children (71%) with aberrant thymus detected at autopsy had features co nsistent with DiGeorge syndrome, and only 5 of the remaining 10 patients ha d a normal mediastinal thymus present. Our patient had normal serum calcium levels after excision and a mediastinal thymus was visualized on MRI. Biospy is required for diagnosis of cervical thymus and should also be cons idered to exclude other causes. MRI is helpful in delineating the presence, position, and extent of thymic tissue. Immunologic sequelae or recurrence after resection of an aberrant cervical thymus has not been reported.