Abstract
The thymus, a vital immune organ in humans, plays a crucial role in the differentiation and development of T cells. Its normal development commences around the fourth week of gestation, originating from the ectoderm of the third branchial cleft and the endoderm of the third parotid pouch. By the 7-8th week of gestation, the primary thymus migrates towards the central axis. However, various factors may disrupt this process, leading to congenital anomalies such as incomplete descent of thymus tissue. Persistence of residual thymus tissue can result in the formation of ectopic thymus. Although ectopic thymus is rare in clinical practice, sporadic cases have been reported in the neck or mediastinum, with fewer occurrences in the pericardium, chest wall, axilla, and thyroid gland. It is estimated that ectopic thymus accounts for approximately 0.4% of neck masses, and improper removal may predispose the child to immune deficiencies. This article focuses on a neonatal patient presenting with respiratory failure, where a foreign body was discovered in the oral cavity during weaning from mechanical ventilation. Subsequently, the tumor progressively enlarged postextubation. Surgical excision of the tumor revealed pathological abnormalities upon hematoxylin-eosin (HE) staining, confirming ectopic thymus tissue. B-ultrasound examination confirmed the presence of thymus tissue, and the child's condition improved, leading to hospital discharge. Follow-up assessments showed no evidence of immune deficiency in the child.