Mediastinal Tumors
Marcus E. Eby
The mediastinum is the central compartment of the thoracic cavity, which is surrounded by loose connective tissue and enclosed laterally by the left and right pleurae.
The mediastinum is the most common location of chest masses in children where a wide variety of both benign and malignant tumors may occur.1
Mediastinal tumors are classified based on 1 of 3 mediastinal compartments (anterior, middle, or posterior) in which they originate (Figure 52.1).
ANTERIOR MEDIASTINUM
Normal Contents
Thymus gland, internal mammary artery and vein, lymph nodes, and adipose tissue
Boundaries
Anterior: sternum
Posterior: the anterior pericardium
Lateral: parietal pleurae
Superior: imaginary line extending from sternal angle to T4 vertebrae
Inferior: surface of diaphragm
Most Common Anterior Mediastinal Neoplasms
Mnemonic: 4Ts = Teratoma (and other germ cell tumors), Terrible lymphoma, Thymoma, and Thyroid neoplasms (from ectopic thyroid tissue)
MIDDLE MEDIASTINUM
Normal Contents
Pericardium and its contents, ascending aorta, superior and inferior vena cava, brachiocephalic artery and vein, central portion of pulmonary arteries and veins, phrenic and upper vagus nerves, trachea, the main bronchi, and lymph nodes
 Figure 52.1 Lateral chest radiograph showing mediastinal divisions. The anterior mediastinum (Ant Med) lies posterior to the sternum and anterior to a line drawn along the anterior tracheal wall in the upper mediastinum and the posterior border of the heart in the lower mediastinum. The posterior mediastinum (Post Med) lies posterior to a line 1 cm behind the anterior margin of the vertebral column and anterior to the chest wall. The middle mediastinum (Mid Med) lies between these. (Reprinted with permission from Webb WR, Higgins CB. Thoracic Imaging. 2nd ed. Philadelphia, PA: Wolters Kluwer/Lippincott Williams & Wilkins Health; 2010.) |
Boundaries
Anterior and posterior: the pericardium
Lateral: parietal pleurae
Superior: imaginary line extending from sternal angle to T4 vertebrae
Inferior: surface of diaphragm
Most Common Middle Mediastinal Neoplasms Bronchogenic Cyst
Lymphoma, cardiac tumor, cystic hygroma, pericardial cyst
POSTERIOR MEDIASTINUM
Normal Contents
Descending aorta, esophagus, thoracic duct, azygos and hemiazygos veins, and lymph nodes
Boundaries
Anterior: the posterior pericardium
Posterior: T5-T12 vertebrae
Lateral: parietal pleurae
Superior: imaginary line extending from sternal angle to T4 vertebrae
Inferior: surface of diaphragm
MOST COMMON NEOPLASMS
Neurogenic tumors, meningomyelocele, neuroenteric abnormalities
Note: the most common pediatric mediastinal mass = neurogenic tumor (˜20% of all mediastinal tumors), usually found in the posterior mediastinum.2
As mediastinal masses can be either benign or malignant, definitive tumor diagnosis via biopsy (obtained via CT guided, bronchoscopy, or surgical) is desired before definitive intervention to determine the nature of the tumor and whether chemotherapy might reduce the size of the tumor for easier resection if indicated.2
Neurofibroma
OVERVIEW
Neurofibromas are nerve-sheath tumors that can arise from peripheral nerves, sympathetic ganglia, or mediastinal chemoreceptors of the paraganglion system3,4
Most common benign tumor of the mediastinum in children
Most frequently located in the posterior mediastinum
Note: neurofibromas can present in isolation or as one of multiple tumors seen in neurofibromatosis type 1
PRESENTATION
Often presents with tracheal compression as tumor grows in size, resulting in upper respiratory symptoms or with the development of scoliosis; usually first suspected on plain radiographs and confirmed with MRI (Figure 52.2)
SURGICAL INTERVENTION
Surgical resection is the standard treatment option. A thoracoscopic approach is increasingly used to access neurogenic tumors of the posterior mediastinum.5
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