The anterior mediastinum is the most common location of a thoracic tumor in children The “4 Ts” of the anterior mediastinal tumors include “terrible lymphoma,” “teratoma,” “thymoma,” and “thyroid carcinoma.” The latter three are rare Nonmalignant conditions with AMM include adenopathy associated with infection, sarcoid, and normal thymus Common lymphomas ( Table 98.5 ) in the anterior mediastinum include T-cell lymphoblastic lymphoma (or T-cell ALL with an associated AMM), Hodgkin lymphoma, and diffuse B-cell large cell lymphoma Lymphoma can also occur in the middle mediastinum, which can also be the site of masses associated with pulmonary sequestration and other developmental anomalies “Teratoma” of the mediastinum includes benign and malignant germ cell tumors Posterior mediastinal masses include neuroblastoma and other neurogenic tumors such as malignant peripheral nerve sheath tumors (especially in patients with neurofibromatosis, type 1), or benign lesions such as schwannoma Primary lung tumors are vanishingly rare in childhood but presentation of lung metastasis at diagnosis or relapse is not uncommon Many pediatric sarcomas, some lymphomas, germ cell tumors, Wilms tumor, and rarely neuroblastoma can present or recur with lung metastasis These typically involve multiple small or large lung nodules in the pulmonary parenchyma or are pleural based Askin tumor is a unique PNET chest wall tumor that occurs in children and young adults Clinical Considerations Clinical Recognition Tumors in the anterior and middle mediastinum often present with respiratory symptoms ranging from mild cough to severe respiratory distress ( Fig 98.1 ) These tumors can compress the great vessels and cause SVC syndrome When asymptomatic they may be identified during evaluation for nonspecific systemic symptoms or even discovered on a chest radiograph performed for another reason In contrast, posterior mediastinal masses are frequently identified on a chest radiograph performed for another reason They may, however, cause local pain from nerve root involvement and/or cord compression (see “Tumors in and Around the Spinal Cord” section) The initial complaints associated with pulmonary metastasis may include respiratory insufficiency, postobstructive infection, foreign body–type symptoms, or hemoptysis Pulmonary nodules may be discovered on a chest radiograph Pulmonary effusions can be the presenting sign of childhood cancer Effusions can be caused by malignant cells in the pleural space or from obstruction of lymphatic drainage Effusions are common with AMM due to leukemia or lymphoma and can also occur with posterior mediastinal neuroblastoma, lung metastasis, and chest wall tumors They may be symptomatic or asymptomatic The