A3-month-oId girl presented to the emergency department with a history of increased work of breathing, worsening congestion, and cough. Two days previously, she was seen in the ED, diagnosed with otitis media (right tympanic membrane retracted), given antibiotics, and sent home. At that time, there was noted to be congestion and cough, but the lungs were clear to auscultation and her oxygen saturation was 100%.
On this second visit, she had a temperature of 37.1° C, a pulse of 160 bpm, a respiratory rate of 80 per minute, and an oxygen saturation of 96%. Retractions were seen, and auscultation revealed only fair aeration with wheezing. Otoscopie examination showed a slightly erythematous tympanic membrane on the right. A chest radiograph was obtained.
The radiograph showed normally expanded lungs without focal consolidation, and a rapid respiratory syncytial virus (RSV) test was positive. The patient was diagnosed with RSV bronchiolitis, sent home with inhaled albuterol, and told to complete her course of antibiotics. A follow-up appointment for a chest computed tomography (CT) was also arranged to evaluate the additional finding seen on the chest radiograph: a 2cm round opacity projecting to the left of midline at the T8-T9 level (see Figure 1).
Figure 1. Frontal radiograph of the chest showing an oval, well-circumscribed mass (white arrows) overlying the cardiac silhouette, inferior to the left mainstem bronchus (black arrows). The mass was not visible on the lateral view.
A CT of the chest was obtained 2 weeks later (see Figure 2, page 314), showing a cystic (fluid density) mass in the left paraspinal region, without significant enhancement, calcification, or extension into a neural foramen.
Based on these findings, the most likely diagnosis would be a bronchogenic cyst, the most common congenital intrathoracic cyst.1
Bronchogenic cysts are formed by abnormal budding of the ventral diverticulum of the foregut, leading to a focal duplication of the tracheobronchial tree. The cysts are lined with ciliated columnar or cuboidal epithelium and may contain thin fluid or mucus. Bronchogenic cysts are usually located in the mediastinum, adjacent to and often attached to one of the major airways. Intrapulmonary lesions may fill partly or completely with air because of communication with an airway.1-3
Early in life, these cysts may present with respiratory distress caused by mass effect and compression of normal structures. Later in life, a bronchogenic cyst may remain asymptomatic until infection occurs.3,4 In one series, all patients (including infants) presented with respiratory difficulty secondary to infection of the cyst.5 Surgical resection is recommended.1,3
On chest radiographs, bronchogenic cysts most often appear as solitary, well-defined, mediastinal or hilar masses. Gas may be seen within a cyst if it is infected or communicates with the tracheobronchial tree. Esophagram may demonstrate extrinsic mass effect on the esophagus, if the cyst is located in an appropriate location. On CT, little mass effect is seen. The attenuation (density) of the contained fluid depends on its composition, but is usually less than soft tissue, although fluid of higher attenuation may be seen if calcium is present. On magnetic resonance imaging (MRI), fluid-filled cysts are typically of low signal on T1 -weighted images and high signal on T2- weighted images. However, if the cyst contains proteinacious fluid, the T1 -weighted signal may be intermediate or increased. The cyst should not enhance with contrast administration. Ultrasound may be useful if the cyst is near the chest wall, and in some cases, the cyst has been identified prenatally.1,2,3,7
Figure 2. Axial (A) and coronal (B) CT images of the chest demonstrate the fluid attenuation mass (white arrows) adjacent to branchial structures, vascular structures, and lung. The esophagus, containing a small amount of air, is distant, on the opposite side of the aorta (black arrow).
The differential diagnosis for an intrathoracic cystic mass would include esophageal duplication cyst, neurenteric cyst, meningocele, lymphangioma, or congenital pulmonary airway malformation (CPAM, previously known as congenital cystic adenomatoid malformation, or CCAM). A round pneumonia or pulmonary abscess should also be considered in the setting of an acutely ill patient.1,6
Like bronchogenic cysts, esophageal duplication cysts and neurenteric cysts result from abnormal budding of the foregut. The imaging characteristics of an esophageal duplication cyst are nearly identical to those of a bronchogenic cyst, although most bronchogenic cysts are in the middle mediastinum and esophageal duplication cysts are in the posterior mediastinum. Pathology can distinguish between the two by the presence of cartilage in a bronchogenic cyst. These cysts are surgically resected as well.1,3,7 Neurenteric cysts are also in the posterior mediastinum, but have a high association with spinal cord and vertebral anomalies. Anterior or lateral meningoceles are frequently associated with kyphoscoliosis, and occur most frequently in patients with neurofibromatosis.1
Lymphangiomas most frequently arise in the neck but can extend into the mediastinum; fewer than 1 % of lymphangiomas are confined to the mediastinum. Although these lesions may be invasive, on imaging they are often well-circumscribed lesions that mold to the mediastinal contours and envelop the great vessels. Ultrasound (US) usually shows a multicystic mass rather than a single cyst. There may be mild contrast enhancement on CT. Surgical excision is the treatment of choice, if possible.1,3
The CPAM is a much more complex lesion, "characterized by overgrowth of bronchial structures at the expense of alveoli associated with an abnormal supplying airway."6 These are classified into three types: type I is macrocystic (>2 cm) and could have an appearance similar to our patient's lesion; type II (smaller cysts) and type III (microcystic/solid) lesions can have pathologic features overlapping with tracheal atresia, bronchial atresia, sequestration, bronchogenic cyst, and congenital lobar hyperinflation (CLH, previously known as congenital lobar emphysema, or CLE).1,2,6 Like bronchogenic cysts, these lesions can become infected and may not present until this occurs. However, fetal diagnosis is becoming more frequent, and these lesions can be seen by both prenatal US and MRlP Treatment of choice is surgical resection to prevent infection and development of malignancy in the cyst wall.1,3
One month after the CT, our patient underwent a throacotomy. The cyst was seen to arise from the mediastinum and appeared to be attached to the bronchus of the left lower lobe. Pathology confirmed the diagnosis of a bronchogenic cyst.
1. Kuhn JP, et aJ, eds. Coffey's Pediatric Diagnostic Imaging, 10th ed. Mòsby; Philadelphia: 2004.
2. Winters WD, Effmann EL. Congenital masses of the lung: prenatal and postnatal imaging evaluation. J Thorac Imaging. 2001; 16(4): 196-206.
3. Shields TW, et al, eds. General Thoracic Surgery, 6th ed. Lippincott Williams & Wilkins; Philadelphia: 2005.
4. Hashemzadeh S, Aslanabadi S, Jafari Rouhi JH, Azhough R, Kaleibar NA. Congenital malformations of the lung. Indian J Pediatr. 2007;74(2): 192-194.
5. Schwartz MZ, Ramachandran P. Congenital malformations of the lung and mediastinum - a quarter century of experience from a single institution. J Pediatr Surg. 1997;32(1): 44-47.
6. Newman B. Congenital bronchopulmonary foregut malformations: concepts and controversies. Pediatr Radiol. 2006;36(8): 773-791.
7. Berrocal T, Madrid C, Novo S, Gutierrez J, Aronjilla A, Gomez-Leon N. Congenital anomalies of the tracheobronchial tree, lung, and mediastinum: embryology, radiology, and pathology. Radiographics. 2043;24(1):e17.