title: Enlarged mediastinal air cyst in a patient with bronchial diverticula localized in the left main bronchus: a case report with surgical and bronchoscopic findings.
abstract: BACKGROUND
  A mediastinal air cyst is a rare computed tomography (CT) finding. Once the lesion is identified, it is difficult to diagnose and treat. Meanwhile, bronchial diverticula have been reported as a CT finding observed in certain pulmonary pathologic conditions. We encountered the case of an enlarged mediastinal air cyst accompanied with bronchial diverticula and upper lobe-dominant fibrous changes of the lung.
  
  
  METHODS
  A 69-year-old man with a chronic cough who had regularly visited a chest physician for upper lobe-dominant pulmonary fibrosis was referred to our hospital for the examination of an enlarged mediastinal air cyst. Chest CT exhibited an air cyst (size, 30 mm) connected to the lumen of the left main bronchus (LMB) and multiple tiny outpouches only on the LMB. Flexible bronchoscopy showed bubbling from slits or indentations of the bronchial mucosa only in the LMB but not in the right main bronchus or lobar bronchus. For therapeutic diagnosis, we removed the air cyst. Based on clinical, surgical, and pathological findings, we diagnosed the air cyst as an enlarged bronchial diverticulum.
  
  
  CONCLUSIONS
  This is the first case wherein bronchoscopic and surgical findings of bronchial diverticula and an enlarged bronchial diverticulum are reported. There are possible pathogenic mechanisms in cases of pulmonary disease that are attributable to enlargement of the bronchial diverticula.
authors.affiliation: Department of Thoracic Surgery, Faculty of Medicine, University of Tsukuba, 2-1-1 Jyounan, Hitachi, Ibaraki, 317-0077, Japan. ichimura@md.tsukuba.ac.jp.|Department of Thoracic Surgery, Hitachi General Hospital, Hitachi, Japan. ichimura@md.tsukuba.ac.jp.
authors.forename: Hideo
authors.identifier: http://orcid.org/0000-0002-2779-0108
authors.initials: H
authors.lastname: Ichimura
authors.affiliation: Department of Thoracic Surgery, Tsukuba Medical Center Hospital, Tsukuba, Japan.
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Ozawa
authors.affiliation: Department of Radiology, Tsukuba Medical Center Hospital, Tsukuba, Japan.
authors.forename: Masanari
authors.initials: M
authors.lastname: Shiigai
authors.affiliation: Department of Radiology, Tsukuba Medical Center Hospital, Tsukuba, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Shiotani
authors.affiliation: Department of Pathology, Tsukuba Medical Center Hospital, Tsukuba, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Kikuchi
authors.affiliation: Department of Thoracic Surgery, Faculty of Medicine, University of Tsukuba, 2-1-1 Jyounan, Hitachi, Ibaraki, 317-0077, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Sato
keywords: Bronchial diverticula; Mediastinal air cyst; Surgery; Upper lobe-dominant pulmonary fibrosis