Bronchogenic cysts are foregut-derived cystic malformations of the respiratory tract. They are usually located within the mediastinum at an early stage of gestation or in the lung at a later stage. However, their location can be anywhere along the developmental pathway of the foregut in an ectopic site. Bronchogenic cysts characteristically exhibit clinical and radiological polymorphism. They pose a differential diagnostic problem, mainly with hydatid disease in endemic countries. The treatment of all bronchogenic cysts has its basis as complete surgical excision, and their definitive diagnosis is established primarily by histopathological examination of the surgical specimen. Prognosis is excellent with no recurrences in case of complete resection.
The genesis of bronchogenic cysts is from the abnormal or late budding of the embryonic ventral lung bud or the tracheobronchial tree which occurs between the 26th and 40th days of gestation. This abnormal bud subsequently differentiates into a fluid-filled, blind-ending pouch. The location of bronchogenic cyst depends on the embryological stage of development at which the anomaly occurs. When the abnormal budding happens during early development, the cyst occupies the tracheobronchial tree. Cysts that arise later are more peripheral and may involve the lung parenchyma.
Bronchogenic cysts are rare cystic lesions, with prevalences of 1 per 42,000 and 1 per 68,000 admissions in two hospital series. They are slightly more frequent in men and often remain undiscovered until the third or fourth decade of life. They account for 10 to 15% of mediastinal tumors and 50 to 60% of all mediastinal cysts. They originate preferentially in the middle mediastinum, including the right paratracheal area and the tracheal carina.
Classification of mediastinal bronchogenic cysts is in five types according to their location:
Intrapulmonary bronchogenic cysts represent 20 to 30% and most commonly involve the lower lobes. They have no predilection for the right or left side.
The other locations of bronchogenic cysts are rare and include the pericardium, the pleura, the neck, the diaphragm, and the retroperitoneum.
Macroscopic findings of bronchogenic cysts :
The definitive diagnosis of bronchogenic cysts derives histological examination of the surgical specimen.
Histological findings of bronchogenic cysts :
In pediatric patients: bronchogenic cysts may cause life-threatening compressive symptoms.
In adults: bronchogenic cysts are often incidental radiologic findings. Pulmonary bronchogenic cysts are more likely to be symptomatic than mediastinal cysts, and 86.4% of symptomatic patients have a complicated cyst.
Computed tomography scan:
It is the investigation of choice. The CT density of bronchogenic cysts is variable from typical water density to high density related to blood, increased calcium content, anthracotic pigment, or increased protein content of the fluid.
Magnetic resonance imaging (MRI):
Magnetic resonance imaging is better than CT scan at delineating anatomic relations and the definition of the cyst. The MRI appearance depends on the cyst’s content. On T1-weighted images, the intrinsic signal intensity varies from low to high, depending on the cyst contents. T2-weighted images show high signal intensity. Enhancement after contrast injection is frequently absent.
The treatment of patients with bronchogenic cysts depends on symptoms at presentation and the patient’s age. Surgical resection alleviates symptoms, prevents complications and establishes the diagnosis of bronchogenic cysts.
There has been a recent rise in the use of thoracoscopic techniques for resection of bronchogenic cysts in adults. The benefits of thoracoscopy include decreased scarring, reduced pain, and shorter hospitalization. Complicated bronchogenic cysts usually require thoracotomy for more extensive resection.
The resection must be complete because of the risk of recurrence after incomplete surgical removal. The treatment of asymptomatic bronchogenic cysts remains controversial. Most authors seem to advocate a surgical approach to prevent complications.
Intrapulmonary bronchogenic cysts:
Lobectomy is the procedure of choice. However, in peripheral bronchogenic cysts or patients with limited lung function, a conservative procedure as a total pericystectomy, a wedge resection, or segmentectomy are recommended.
Mediastinal bronchogenic cysts:
The presence of adhesions especially in complicated forms of mediastinal bronchogenic cysts can lead to incomplete resection. Thus, resection or destruction of mucosa is a requirement to prevent accumulation of fluid and late recurrence.
An alternative option for bronchogenic cysts is close imaging surveillance to ensure temporal stability.
Radiological differential diagnosis:
Histological differential diagnosis:
According to some authors, bronchogenic cysts lead to complications in 45% of patients, but complications do not increase morbidity and death.
Complications of bronchogenic cysts include:
Superior vena cava syndrome
Stenosis of pulmonary artery
Fatal air embolism in an airplane passenger
Fatal myocardial infarction (MI) secondary to compression of the left main coronary artery
Bronchogenic are rare lesions. In children, they often tend to be symptomatic, but in adults, they are often an incidental finding. However, because their diagnosis and management are not straightforward, the disorder is best managed by a multidisciplinary team that includes a radiologist, pediatrician, thoracic surgeon, and a pulmonologist.