“…3,4,6,7 The cause of apical fibrobullous changes is unknown, but several theories have been suggested. These include diminished upper lobe ventilation due to chest wall rigidity, 9 altered apical mechanical stress due to rigid thoracic spine, 3 recurrent pulmonary infection due to impaired cough, and respiratory mechanics as a result of thoracic rigidity. 2 Other theories include prior thoracic irradiation, repeated aspiration pneumonitis secondary to esophageal muscle dysfunction, 10 and cricoarytenoid joint disease.…”