Congenital thymoma

Abstract

Thymomas are a heterogeneous group of tumors arising from the epithelium of the thymus. They are categorized by the proportion of neoplastic epithelia to lymphocytes and by the degree of cytologic atypia. Thymomas constitute 0.2-1.5% of all malignancies and nearly all occur in patients over 20 years. We reviewed the available literature and found less than 50 cases of thymoma reported in children (<18 years of age), the youngest being 4 years old, and no cases in newborns. They represent less than 1% of all mediastinal tumors in children. Due to the limited number of cases in the pediatric population, the diagnosis and treatment in this population is extremely challenging. Thymomas in all age groups may be associated with paraneoplastic syndromes, being myasthenia gravis the most common, which is associated with a worse prognosis in the pediatric population. We present the first case of a newborn infant with congenital thymoma. This case demonstrates a rare tumor in an unusual age group and emphasizes the importance of multidisciplinary teamwork in the decision-making and management of this condition.

Keywords: Congenital Abnormalities; Hospitals, Pediatric; Thymoma; Thymus Hyperplasia; Thymus Neoplasms.

Figure 1. A – Sagittal contrast-enhanced thoracic computed tomography (CT) demonstrates a large, heterogeneously enhancing, anterior mediastinal mass. No calcification or necrosis is noted. The mass causes passive atelectasis of the adjacent right middle and upper lung lobes; B – Axial contrast-enhanced thoracic CT demonstrates a large anterior mediastinal mass with heterogeneous enhancement. The lesion exerts mass effect on the great vessels, displacing them posteriorly. Extrinsic compression on the tracheal is also noted, but the tracheal remains patent. No area of necrosis, calcification, or lymphadenopathy noted.

Figure 2. A – Hematoxylin eosin-stained section reveals mixed population of pleomorphic thymocytes in a background of bland appearing lymphocytes. Immunohistochemical stain reveals large proliferation of (B) CK AE1/AE3 positive thymocytes, and (C and D) CD3 and CD1a positive thymic lymphocytes.