<prompt> After suffering a respiratory tract infection, a 64-year-old female biochemist develops chronic lung disease requiring intubation in the ICU for an 8-week period. Tracheal stenosis is noted. What is the most likely cause of tracheal stenosis?Prolonged intubationTuberculosisSclerodermaRiedel struma fibrous thyroiditis  <response>: Any object that compromises the blood supply to the tracheal mucosa or cartilage can cause stenosis. When the mean intramural pressure exceeds 20-30 mm Hg, damage may be anticipated. Riedel struma is a rare fibrosing thyroid condition, which must be differentiated from carcinoma and may cause severe tracheal stenosis. Achalasia is a neuromuscular defect at the lower end of the esophagus causing dysphagia, because of nonmechanical esophageal obstruction. 