A 69-year-old man, who had regularly visited a chest physician for upper lobe-dominant pulmonary fibrosis and chronic cough, was referred to our hospital for the examination of an enlarged air-filled mediastinal cystic lesion detected using chest computed tomography (CT). The patient did not have any smoking history, worked at an iron cast manufacturing industry, and was prescribed antitussives for persistent cough by his physician. In laboratory studies upon admission, levels of white blood cells (4000/μL), lactate dehydrogenase (193 IU/L), C-reactive protein (0.04 mg/dL), and KL-6 (363 U/mL) were in the normal ranges. A pulmonary function test showed restrictive ventilatory impairment (vital capacity (VC) 2.16 L; %VC 60.7%; forced vital capacity (FVC) 2.33 L; forced expiratory volume in 1 s (FEV1) 2.25 L; FEV1/FVC 96.6%). CT showed a mediastinal air cyst (size 30 mm) adjacent to the LMB and dominant fibrous changes in the subpleural region in both upper lobes (Fig. 1a). A reconstructed frontal plane CT scan showed that the lumen of the cystic lesion was connected to that of the LMB through a thin tunnel, and that, many tiny air spaces extended from the LMB wall (Fig. 1c, d). Flexible bronchoscopy showed a round-shaped lumen of the LMB and bubbling from slits or indentations of the bronchial mucosa only in the LMB, but not in the right main bronchus or lobar bronchus (Fig. 2 and Additional file 1: Video 1). In comparison with the chest radiographs obtained during the first visit (Fig. 3a) and 4 years earlier (Fig. 3b), progression of volume loss in the right upper lobe was apparent. Compared with CT obtained 4 years earlier (Fig. 1b), the current CT (Fig. 1a) showed an enlargement of the air cyst over time.
Additional file 1: Video 1. Bronchoscopy of the left main bronchus showing bubbles from the slits or indentations of the mucosa (arrow). (7 MB)
For therapeutic diagnosis, we performed a removal of the cystic lesion under mini-thoracotomy using an 11-cm incision and two surgical ports (operative time 230 min; volume of blood loss 170 mL; Fig. 4 and Additional file 2: Video 2). Since it was difficult to identify the cystic lesion in the subaortic region (where it should exist) and fibrotic change of the region was apparent, we first identified the left recurrent nerve to avoid an accidental injury and subsequently attempted to dissect the cystic lesion. When we unintentionally made a hole in the wall of the lesion, we found the smooth, white-colored cystic lumen that enabled us to recognize the extent of the lesion. We nearly removed the entire cystic lesion that did not have adventitia. Since the cystic wall adjacent to the LMB could not be dissected due to its firm adhesion, an area of approximately 1 × 0.5 cm of the LMB was left with retained lesion tissue. When we completed a dissection of the whole LMB circumferentially, we did not recognize small diverticula that appeared on the preoperative CT, which indicates that the diverticula remained intact in the bronchial sheath.
Additional file 2: Video 2. Intraoperative video showing removal of the cystic lesion and the circumferential coverage of the left main bronchus with a polyglycolic acid sheet. (11 MB)
Air leakage from the LMB was seen only at the site where the cystic wall had not been dissected and was stopped by placing a Z-suture using 4–0 PDS II (Ethicon, Inc., Somerville, NJ). To reinforce the suture site and prevent another enlargement of tiny BDs, the patient underwent circumferential covering of the whole LMB with a polyglycolic acid (PGA) sheet. Finally, fibrin glue was applied on the PGA sheet.
The patient was discharged on postoperative day 11 without any adverse events.
Upon pathological examination, the inner membrane of the lesion was covered with ciliated bronchial epithelial cells. The wall of the lesion consisted of unstructured fibrous tissue without bronchial gland tissue nor cartilage (Fig. 5). Follow-up bronchoscopy was performed 6 months postoperatively and indicated a disappearance of the bubbling as well as the resolution of the chronic cough to that of pre-procedural levels. The antitussive agent was discontinued postoperatively. Follow-up CT scans obtained at 1 year postoperatively showed no recurrence of air space or further development of BDs. Thereafter, he was monitored and treated by his prior chest physician. He died of chronic respiratory failure due to progression of upper lobe-dominant pulmonary fibrosis 20 months after the surgery.