Bronchogenic and enteric cysts, which are commonly located in the middle or posterior mediastinum, represented 7.1% of all of the mediastinal masses in the reported review and accounted for 18.4% of the benign lesions. Although malignant thymoma, germ cell tumors, and Hodgkin disease may all have cystic components, the majority of cystic mediastinal tumors are benign lesions that are congenital in origin. In the reported review, gastroenteric duplications (22) were less common than bronchogenic cysts (32).
Congenital mediastinal cysts generally arise from the foregut as a result of anomalous budding of the primordia of the esophagus or tracheobronchial tree. Each of the 3 types of foregut cysts (bronchogenic cysts, enteric duplications, and the rare neuroenteric cysts) has characteristic histologic and anatomic features. Occasionally, the pathologic characteristics of both enteric duplications and bronchogenic cysts coexist, and these composite structures are referred to as bronchopulmonary foregut malformations.
On a CT scan, a foregut cyst usually appears as a smooth, rounded cystic mass with homogeneous attenuation. The lesion typically has a thin wall and is commonly located in the carinal, paratracheal, or paraesophageal region. The cyst contents generally have attenuation values similar to those of water, but higher levels can be observed if the lesion contains mucus, blood, or debris. Bronchogenic and enteric cysts are not enhanced in the presence of intravenous contrast.
The respiratory tract develops as a ventral bud off of the primitive foregut on about the 22nd day of gestation, and division into left and right main stem bronchi is usually complete by day 26. Abnormal budding from the tracheobronchial tree is believed to result in bronchogenic cysts. These lesions may be completely encapsulated, or they can communicate with the airway. Although most bronchogenic cysts arise in the mediastinum, they also occur in the pulmonary hilum, the lung parenchyma, or the neck, and can even be found below the diaphragm. Bronchogenic cysts are usually lined with ciliated columnar or cuboidal epithelium and have a fibromuscular wall that may contain both cartilage and bronchial mucous glands.
Bronchogenic cysts are a well-recognized cause of respiratory distress in newborns and these cysts can also produce recurrent pulmonary infections in older infants and children. In a review of 20 patients with bronchogenic cysts, the most common presenting symptom was fever, followed by recurrent pneumonia, a cervical mass, and respiratory distress. On standard chest radiographs, bronchogenic cysts usually appear as radiolucent spherical lesions that are variable in size and may cause a mediastinal shift (Fig. 28-8A and B). On CT scanning, bronchogenic cysts appear as well-defined, spherical, nonenhancing masses. If the cyst is infected or filled with secretions, it may be radiodense. If there is communication with the tracheobronchial tree, an air-fluid level will frequently be observed.
A. Posteroanterior chest radiograph obtained for the evaluation of persistent wheezing that failed to respond to bronchodilator therapy. A retrocardiac mass is noted on the right. B. With computed tomography a thin-walled apparently cystic lesion is observed adjacent to the left lower lobe bronchus.
Bronchogenic cysts should be resected. A thoracoscopic approach can be used for easily accessible lesions. If a thoracotomy is elected, a muscle-sparing technique is most appropriate. If a complete resection is difficult because a portion of the cyst wall is densely adherent to the bronchus, esophagus, or trachea, the mucosa should be stripped and a segment of the cyst wall left behind.
Enteric and Neuroenteric Cysts
Enteric cysts, also called enterogenous cysts and enteric duplications, have somewhat thicker muscular walls and are typically spherical or tubular in configuration. Because these lesions are lined with mucus-producing epithelium, they gradually enlarge and usually produce symptoms in infancy or early childhood resulting from the compression of adjacent organs.
Esophageal duplications, a subset of enteric cysts, constitute 15% of all gastrointestinal duplications. These lesions may contain cartilage and respiratory epithelium similar to bronchogenic cysts, and they tend to occur in older children. Esophageal duplications typically have well-developed muscular walls lined with gastric or intestinal mucosa.
Neuroenteric cysts are the least common type of congenital mediastinal cyst. They communicate with the meninges through a defect in the neurospinal axis and may be suspected on a chest radiograph because of the associated vertebral anomalies. A neuroenteric cyst has thin, fibrous walls lined with simple or pseudostratified epithelium. These lesions may produce neurologic symptoms if spinal cord compression occurs, and meningitis is a real threat, particularly if there is open communication with the gastrointestinal tract. Surgical management may require the assistance of colleagues in both neurosurgery and orthopedics in order to ensure proper closure of the dural membrane and stabilization of the vertebral column.