Mediastinal Masses

Outcomes

Children with Stage I disease have a 90-95% long-term survival on multiple drug chemotherapy with or without radiation therapy. Stage II patients have a 75% survival rate. In advanced cases, a multiple drug program offers about 70% relapse-free survivals.

A major complication of therapy is tumor lysis syndrome that results from rapid breakdown of malignant cells. Gastrointestinal problems of bleeding, obstruction and rare perforation are also part of this syndrome.

Mediastinal masses are varied and present at all ages, from newborn to adolescence. There is a wide spectrum of pathology that may include congenital, inflammatory, infectious, and neoplastic processes. Because of the limited space and confined geometry of the region, masses can interfere with both the respiratory and cardiovascular systems, sometimes with grave results.

Understanding of the anatomical subdivisions of the mediastinum and the relative frequency of specific pathology in these subdivisions aids in the differential diagnosis (Table 9.7).

Table 9.7

Mediastinal masses in the pediatric population

(data from Robert M.Arensman, 2009)

Note!The mediastinum is the area in the chest between the lungs. It extends from the sternum in front to the vertebral column behind and may be divided for purposes of description into two parts:

v an upper portion, above the upper level of the pericardium, which is named the superior mediastinum (contains the thymus, lymphatics and vascular structures) with its superior limit at the superior thoracic aperture and its inferior limit at the plane from the sternal angle to the disc of T4-T5;

v and a lower portion, below the upper level of the pericardium. This lower portion is subdivided into three parts:

· The anterior mediastinum is the space below the superior compartment, bounded by the pericardium and diaphragm.

· The middle mediastinum contains the pericardium, heart, origins of the great vessels, trachea, mainstem bronchi and lymphatics.

· The posterior mediastinum is bounded by the great vessels anteriorly and the vertebral bodies posteriorly. The normal structures in this space include the esophagus, sympathetic ganglia, thoracic duct, vessels and lymphatics.

Image 9.25 Lateral chest X-ray

As in adults, mediastinal masses in pediatric patients are placed in one of three mediastinal compartments (anterior, middle, posterior) on the basis of the lateral chest radiograph (Image 9.25).

Anterior mediastinal compartment is area surrounded by sternum anteriorly and anterior margin of pericardium posteriorly. Middle mediastinal compartment is bordered by anterior margin of pericardium and imaginary line drawn approximately 1-cm posterior to anterior margin of thoracic vertebral bodies. Posterior mediastinal compartment is area surrounded anteriorly by imaginary line drawn 1-cm posterior to anterior border of thoracic vertebral bodies and posteriorly by paravertebral gutters.

Primary mediastinal masses are rare in children. Approximately one half of the masses are malignant, and of neurogenic or lymphomatous origin. According to different reports, neurogenic tumors predominate before the age of 4 years, while lymphomas are most common beyond age 4 and germ cell tumors are seen in adolescence.

The mediastinal masses can also be categorized as developmental, neoplastic, or inflammatory.

Developmental: For example, the following problems are the best known instances of developmental anomalies producing mediastinal masses.

It is presumed that incomplete separation and tubulization of the esophagus and trachea after the proliferative phase, which normally occurs by the 5th week of gestation, results in foregut duplication. Additionally, these duplication cysts can communicate with the spinal canal and are then referred to as neurenteric cysts.

The thymus develops as paired primordia from the ventral third pharyngeal pouch and descends to an area anterior to the aortic arch during the 7th week of gestation. Incomplete descent or obliteration of its tract may result in a cystic or ectopic thymus in the neck. In the middle mediastinum, bronchogenic cysts develop from abnormal budding of the tracheal diverticulum or ventral portion of the foregut. Pericardial cysts can occur when disconnected lacunae in the mesenchyme fail to coalesce with the developing pericardial sac.

Neoplastic: The most common neoplasm of the anterior mediastinum in children is lymphoma, accounting for up to 45% of pediatric mediastinal masses. Other neoplasms in the anterior mediastinum include germ cell tumors (25%), mesenchymal tumors (15%) and thymic tumors (17%). The majority of these tumors are malignant. Neurogenic lesions (neuroblastoma, ganglioneuroblastoma, ganglioneuroma and schwanoma), which comprise approximately 20% of mediastinal tumors, are usually located in the posterior mediastinum.

Inflammatory: Acute infection of the mediastinum is most often seen following esophageal perforation, as well as after cardiac operation or penetrating chest trauma. However, infection may be the first presentation in developmental conditions, such as thymic cyst, enteric and bronchogenic cysts and cystic hygroma. That is why elective resection is performed for these lesions when they are diagnosed.

Note!Anterior mediastinal masses are most often neoplastic. The most common lesion found in the anterior mediastinum in the pediatric population is lymphoma. However, germ cell tumors, thymomas, and thyroid tumors can occur as well. The middle mediastinum is more likely to be involved with a more congenital anomaly, such as a foregut duplication or bronchogenic cyst. The posterior mediastinum is a characteristic location for neurogenic tumors. Lymphatic and vascular malformations can be present in any of these spaces and are sometimes contiguous with a cervical component.