Background: Bronchogenic cysts are congenital in nature. They are part of a spectrum of congenital abnormalities of the lung including pulmonary sequestration, congenital cystic adenomatoid malformation, and congenital lobar hyperinflation (emphysema).

Pathophysiology: Bronchogenic cysts develop from an abnormal budding of the ventral foregut between the 26th and 40th week of gestation. As such, they are often more appropriately termed foregut duplication cysts.

Frequency:

• In the US: The frequency of bronchogenic cysts is unknown presumably because most patients are asymptomatic. Numerous studies have documented the rare incidence of bronchogenic cysts with an average incidence of 20 cases over a 20-year period.

• Internationally: International frequency is unknown.

Mortality/Morbidity: Though usually an incidental finding, morbidity from bronchogenic cysts has been reported from the cyst becoming secondarily infected or from postobstructive pneumonia. Dysphagia and dyspnea have resulted from compression of a large cyst on the esophagus and airways. Cases have been reported of cyst rupture and hemorrhage within the cyst.

Race: The frequency in different races is unknown.

Sex: Frequency in each sex is unknown.

Age: Bronchogenic cysts are congenital lesions. Large cysts may present in the pediatric population because of compression of the esophagus or trachea or because of infection. In adults, the cysts typically present as an incidental mass in either the mediastinum or the lung.

Anatomy: Bronchogenic cysts are located most commonly in the mediastinum (85%). Common locations include precarinal, paratracheal, and retrocardiac sites. Intrapulmonary bronchogenic cysts are less common (15%).

Histologically, cysts are thin walled, filled with mucoid material, and lined with columnar respiratory epithelium, mucous glands, cartilage, elastic tissue, and smooth muscle.

Clinical Details: In the pediatric population bronchogenic cysts present with fever or difficultly breathing. Adults with bronchogenic cysts are usually asymptomatic. Patients with large mediastinal cysts may present with stridor or dysphagia resulting from mass effect on the trachea or esophagus.

Preferred Examination: Bronchogenic cysts are usually an incidental finding, and differentiating them from other pathologic conditions is important. On conventional radiographs, the appearances of mediastinal or lung masses are nonspecific and should be evaluated further using CT or MRI.

Limitations of Techniques: Chest radiograph is usually adequate for detecting larger mediastinal or lung masses; however, it is limited in differentiating solid masses from fluid.

CT findings are characteristic when the lesion demonstrates water density. If the lesion demonstrates soft tissue density, differentiating the cyst from lymph nodes or other solid lesions is difficult.

MRI findings are usually diagnostic for mediastinal cysts.

Intrapulmonary cysts are difficult to diagnose and must usually be aspirated to confirm the diagnosis.

DIFFERENTIALS

Congenital Cystic Adenomatoid Malformation
Hodgkin Disease, Thoracic
Lung, Nontuberculous Mycobacterial Infections
Lung, Primary Tuberculosis
Non-Hodgkin Lymphoma, Thoracic
Pulmonary Sequestration
Sarcoidosis, Thoracic
Solitary Pulmonary Nodule

Other Problems to be Considered:

Metastatic disease to the mediastinum
Reactive lymph node
Abscess
Pneumatocele

X-RAY

Findings: Mediastinal cysts are visualized as a mediastinal mass on conventional radiographs. Intrapulmonary cysts usually present as a solitary pulmonary nodule unless the cyst contains air.

Degree of Confidence: On conventional radiographs, findings are nonspecific. Mediastinal masses should be evaluated further using CT or MRI to confirm the presence of fluid.

False Positives/Negatives: Difficulty is encountered in determining whether the visualized mass is benign (eg, a bronchogenic cyst) or malignant.