Chest Film Clinic: What caused this man's dyspnea, chest pain, and atrial fibrillation?

A 52-year-old man presented to his primary care physician with shortness of breath for 5 days, right-sided lower thoracic back pain, and dry cough. The patient was a 15-pack-year cigarette smoker who had emigrated from China to the United States in 1989. He had no significant history of occupational exposure or tuberculosis. He had no significant weight loss, and his past medical history was otherwise unremarkable.

On physical examination, the patient was an afebrile, ill-appearing man in moderate respiratory distress, with a respiration rate of 24 breaths per minute. His oxygen saturation on room air was 93%, which dropped to 87% with ambulation. His heart rate was 88 beats per minute and irregular.

On auscultation, the patient had decreased breath sounds at the right lung base, without rales or egophony. An ECG revealed new-onset atrial fibrillation with no evidence of ischemia. The patient's white blood cell count was 10,700/µL, with a normal differential. The remainder of the laboratory workup results were normal.

The patient's posteroanterior and lateral chest radiographs that were obtained on admission are shown below (Figure 1).

Making the diagnosis

The patient's chest radiograph revealed a large mediastinal mass with its epicenter in the subcarinal region (Figure 1). The mass extended laterally to the right hilar region, displacing and compressing the right main bronchus and bronchus intermedius. There was associated volume loss in the right lower lobe and a moderate pleural effusion.

A contrast-enhanced CT scan of the chest revealed a subcarinal cystic mass 9 cm in diameter, with simple fluid attenuation and no evidence of enhancement (Figure 2). The bronchus intermedius was extrinsically compressed and obstructed distally, with associated partial atelectasis of the right lower lobe. Of note, the left atrium was markedly compressed by the adjacent mass.

Based on these imaging findings, the clinical diagnosis of a symptomatic bronchopulmonary foregut cyst was made. The lower lobe atelectasis, associated effusion, and pleuritic chest pain were attributed to the bronchial obstruction, and the atrial dysrhythmia was thought to be caused by left atrial compression. The patient's dyspnea was considered to be the result of the anatomic distortion of both the right lung and the heart.

On admission, anticoagulation was initiated and both the interventional pulmonology and thoracic surgery departments were consulted. A multidisciplinary discussion addressed the diagnostic and therapeutic options. Flexible bronchoscopy was not performed, because it could only confirm the imaging findings and perhaps palliate the airway obstruction with needle aspiration of the cyst and/or deployment of an airway stent.

Since the patient's hemodynamic status was stable and there were no signs of infection, definitive surgery was deemed the most appropriate course of action. The patient underwent a right thoracotomy with resection of the cyst. A small bronchotomy was necessary to completely resect the cyst wall from the membranous aspect of the bronchus intermedius; this was repaired and buttressed primarily through use of a vascularized flap of thymic tissue.

Cultures from specimens of the cyst contents and the pleural fluid (before opening the cyst) were sterile. Pathologic examination revealed a benign cyst lined with respiratory epithelium and confirmed the clinical diagnosis of bronchogenic cyst.

Discussion

Most bronchopulmonary foregut cysts are diagnosed during infancy or childhood from evidence of compromise of the adjacent airway. Cases that escape detection during childhood are likely to present symptomatically during adulthood; about 75% of adults with bronchogenic cysts have symptoms that lead to imaging studies and a definitive diagnosis.¹

Cystic lesions account for about 25% of all mediastinal masses presenting in adulthood.² Most bronchopulmonary foregut cysts originate in the middle mediastinum. The primitive foregut gives rise to most organs and tissues from the pharynx to the ligament of Treitz. Beginning in the fourth week of gestation, the lung bud develops caudally from the laryngotracheal tube. By the fifth week, the single bud has divided into right and left main-stem bronchi, which later develop in the right and left lung. Further branching continues until the 24th week, when the primitive alveoli develop. It is during this period that abnormal bronchi and bronchioles can form large saccular structures, later recognized as bronchogenic cysts.³

As was seen with our patient, the vast majority of patients with bronchogenic cysts are symptomatic at presentation.^4-6 Chest pain, cough, and dyspnea are the most common presenting symptoms.¹

Because of the larger size of adjacent thoracic structures and the frequent use of CT in contemporary medicine, adults are more likely than children to have a cyst detected incidentally. However, most adults with cysts that are initially asymptomatic go on to experience subtle symptoms and/or signs of infection after diagnosis. For example, in a series by St-Georges and colleagues,¹ most adults with initially asymptomatic cysts became symptomatic over time.

A chest radiograph can detect and localize the lesion in 60% to 65% of patients, as it did in our case. The typical appearance is a 2- to 10-cm, smooth, homogeneous, subcarinal mediastinal mass that splays the carina. The presence of an air-fluid level suggests a persistent bronchial communication or complication by secondary infection.

Cross-sectional imaging techniques (either CT or MRI) have become the diagnostic procedures of choice for mediastinal masses. They provide superb anatomic detail regarding the location and structure of the cyst and its relationship to adjacent mediastinal structures. They also provide accurate assessment of the cyst wall and its contents.

The treatment options for bronchogenic cysts include observation, resection, and aspiration.^7,8 Reports of long-term outcomes following aspiration therapy for bronchogenic cysts are limited; however, it appears that aspiration may play a role in high-risk patients who have relative contraindications to general anesthesia and surgery. In general, all symptomatic bronchogenic cysts should be removed.⁹

Infection is the most common complication of "watchful waiting," especially in cysts with persistent bronchial communication. Airway obstruction has been reported, with a higher incidence among children because of the softer nature of their tracheobronchial tree.¹⁰ Rupture of the cyst into the airway, pericardium, and pleural cavity has also been reported.¹¹ The presence of malignancy, although rare, has been documented in several series.^12,13 Compression and/or obstruction of adjacent mediastinal vascular structures have also been reported.¹⁴

Two large studies advocate resection for patients who are asymptomatic.^4,11 They report a trend for asymptomatic lesions to become symptomatic. Moreover, these studies document higher operative morbidity in patients in whom symptomatic lesions are resected than in those who have elective surgery for asymptomatic le- sions. The studies conclude that waiting for symptoms to develop places patients at higher risk.

Traditionally, a thoracotomy with lung- sparing resection (when possible) is the treatment of choice. Recently, videothoracoscopy has been used to resect bronchogenic cysts with minimal morbidity.^2,15,16 Regardless of the operative approach, the goal of the procedure is to completely remove all elements of the cysts--especially the epithelial lining. However, some cysts are found densely adherent to airway or vascular structures, which renders complete excision impossible or impractical.^15-18 In these cases, complete mucosal excision or cautery ablation is necessary to minimize the risk of recurrence. Despite this approach, symptomatic recurrence requiring reoperation has been reported after partial excision.^17,19

The detection of a cystic mediastinal mass in the adult patient should trigger a preoperative evaluation, including cross-sectional imaging with CT or MRI. Resection should be performed--even in asymptomatic patients--because most patients will eventually become symptomatic or secondarily infected. Complete excision, either by thoracotomy or thoracoscopy, is the preferred and most definitive treatment.

The outcome in this case

The patient had an uneventful recovery without recurrence of atrial fibrillation. He was discharged on a regimen of ß-blockers and warfarin on postoperative day 5. After 3 months of anticoagulation, he remained in sinus rhythm and warfarin was discontinued.

The patient continued to complain of cough, although his chest radiograph demonstrated a well-expanded right lower lobe and resolution of the right-sided effusion. Flexible bronchoscopy that was performed 4 months after surgery revealed normal healing at the site of the bronchotomy, with minimal granulation tissue and no bronchial stenosis; a sputum analysis showed no active infection. The patient was asymptomatic 7 months after initial presentation.

Figure 1 - A large mediastinal mass (arrows), with its epicenter in the subcarinal region, is demonstrated in these chest radiographs. The mass splays the carina (C) and compresses the bronchus intermedius (asterisk).

References:

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