Mounier-Kuhn syndrome, also called tracheobronchomegaly, is a rare disorder characterized by marked dilatation of the trachea and main bronchi. The condition arises from atrophy or deficiency of elastic fibers and smooth muscle in the airway wall, which allows the central airways to enlarge abnormally. This structural weakness can impair the clearance of secretions, leading to recurrent respiratory infections and variable dynamic airway collapse. Clinical manifestations are heterogeneous, and some patients remain asymptomatic or present only with nonspecific respiratory symptoms, making the diagnosis easy to miss.

The patient in this case was scheduled for left total hip arthroplasty following a femoral neck fracture. Standing 177 centimeters tall and weighing 74 kilograms, he had a medical history that included hypertension, long-term cigarette smoking, and chronic respiratory symptoms such as recurrent cough, wheezing, and repeated lower respiratory tract infections. Despite these warning signs, no definitive respiratory diagnosis had been established before surgery. Preoperative chest radiography and computed tomography demonstrated interstitial lung changes, but the marked tracheal dilatation visible on the CT scan was not recognized prior to the operation.

Standard monitoring was applied, including electrocardiography, pulse oximetry, and invasive arterial blood pressure measurement. General anesthesia was induced with midazolam, etomidate, sufentanil, and cisatracurium. Endotracheal intubation proceeded uneventfully using a video laryngoscope with a 7.0-millimeter cuffed endotracheal tube. However, once volume-controlled ventilation began with an inspired oxygen fraction of 0.60, a tidal volume of 450 milliliters, a respiratory rate of 15 breaths per minute, an inspiratory-to-expiratory ratio of 1:1.5, and positive end-expiratory pressure of 4 centimeters of water, something was clearly wrong. Peak airway pressure remained abnormally low at just 2 centimeters of water, and the delivered tidal volume was approximately 40 milliliters, indicating severe air leakage.

The anesthesia team immediately inspected the anesthesia machine and breathing circuit but found no abnormalities. Additional cuff inflation failed to improve ventilation, prompting removal of the endotracheal tube to confirm it was intact. Reintubation with a larger 7.5-millimeter cuffed tube did not resolve the leakage either. Fiberoptic bronchoscopy was subsequently performed and revealed marked dilatation of the trachea and both main bronchi extending from the subglottic region distally. The posterior membranous wall appeared widened, and expiratory luminal narrowing exceeding 50 percent was observed. A retrospective review of the preoperative CT images demonstrated marked tracheal dilatation and deformation, with a maximal measured diameter of 38.87 millimeters. Together, the imaging and bronchoscopic findings were consistent with Mounier-Kuhn syndrome.

Under bronchoscopic guidance, the endotracheal tube cuff was repositioned within the relatively narrow subglottic segment. This maneuver restored effective ventilation, with peak airway pressure increasing to 15 centimeters of water and delivered tidal volume reaching approximately 400 milliliters. The patient was subsequently positioned in the right lateral decubitus position, which further improved airway sealing. Surgery then proceeded uneventfully with stable hemodynamics and adequate oxygenation. Repeat bronchoscopy before extubation showed no visible evidence of reflux or aspiration. The patient was extubated in the operating room and transferred to the surgical ward in stable condition.

Unfortunately, the postoperative course was complicated. On postoperative Day 2, the patient developed sudden hypoxemia and decreased consciousness, accompanied by fever, tachycardia, hypotension, and an oxygen saturation of 80 percent. Arterial blood gas analysis showed a PaO2 of 44.5 millimeters of mercury while receiving supplemental oxygen via nasal cannula, with an estimated inspired oxygen fraction of approximately 0.30, and a PaCO2 of 32.9 millimeters of mercury, indicating severe hypoxemia without significant hypercapnia. Emergency endotracheal intubation was performed. Video laryngoscopy revealed copious purulent secretions in the oropharynx, and abundant purulent secretions were aspirated through the endotracheal tube. Bronchoscopy in the intensive care unit demonstrated edematous airway mucosa, purulent secretions, and near-complete airway narrowing during coughing. Laboratory testing showed markedly elevated inflammatory markers, and endotracheal aspirate culture yielded Klebsiella pneumoniae. Aspiration pneumonia was diagnosed. Bedside chest radiography and CT confirmed marked tracheobronchial dilatation, with a substantial gap between the inflated endotracheal tube cuff and the tracheal wall, indicating inadequate airway sealing.

Despite intensive care, the patient showed limited improvement and was eventually transferred to a rehabilitation facility with ongoing ventilatory support. The case underscores that Mounier-Kuhn syndrome can significantly impair mucociliary clearance and cough effectiveness, promoting secretion retention and recurrent respiratory infection. While an inadequate cuff seal may raise concern for perioperative aspiration, no overt aspiration was observed before extubation, and a direct causal relationship could not be established in this instance. Nevertheless, the combination of markedly abnormal airway anatomy, impaired airway clearance, and secretion burden would have favored a more conservative extubation strategy and closer postoperative respiratory monitoring in retrospect.

Looking back, several preoperative findings could have suggested an underlying structural airway abnormality, including long-term smoking, recurrent cough and wheezing, repeated lower respiratory tract infections, and tracheal dilatation visible on the available CT images. Mounier-Kuhn syndrome often goes unrecognized because its clinical manifestations are nonspecific, and central airway enlargement may be overlooked unless the trachea and main bronchi are deliberately assessed. This case reinforces the importance of integrating the respiratory history with careful review of available thoracic imaging during preoperative assessment. When structural airway abnormalities are suspected, advance planning should address airway-device selection, ventilation strategy, availability of bronchoscopic rescue, extubation, and postoperative respiratory support.

The most distinctive intraoperative feature in this case was severe peri-cuff leakage that persisted despite additional cuff inflation, replacement with a larger endotracheal tube, and exclusion of equipment malfunction. Marked tracheal enlargement created a mismatch between the inflated cuff and the tracheal wall, preventing an effective seal. Persistent peri-cuff leakage after common tube-, cuff-, and circuit-related causes have been excluded should therefore raise suspicion of an anatomical airway abnormality. Fiberoptic bronchoscopy proved particularly useful because it directly demonstrated the abnormal airway anatomy and guided repositioning of the cuff to a relatively narrow subglottic segment, immediately restoring effective ventilation. Similar strategies have been reported in patients with previously unrecognized tracheobronchomegaly presenting with severe air leakage after tracheal intubation. Bronchoscopy should be viewed not as routine preoperative screening, but as a targeted diagnostic and therapeutic tool when otherwise unexplained peri-cuff leakage persists. This case serves as a powerful reminder that rare airway disorders can emerge at the most critical moments, and that vigilance, bronchoscopic expertise, and individualized perioperative respiratory planning can make the difference between a manageable challenge and a life-threatening complication.

Subject of Research: Mounier-Kuhn syndrome presenting as severe intraoperative airway leakage during general anesthesia in an elderly surgical patient

Article Title: Severe Intraoperative Airway Leak Revealing Undiagnosed Mounier‐Kuhn Syndrome in an Elderly Patient

Article References: Chen, X., Miao, S., Zhou, D., & Zhang, X. (2026). Severe Intraoperative Airway Leak Revealing Undiagnosed Mounier‐Kuhn Syndrome in an Elderly Patient. Clinical Case Reports, 14(10), Article e73738. https://doi.org/10.1002/ccr3.73738

Image Credits: AI Generated

DOI: 10.1002/ccr3.73738

Keywords: Mounier-Kuhn syndrome, tracheobronchomegaly, intraoperative airway leak, endotracheal intubation, fiberoptic bronchoscopy, aspiration pneumonia, perioperative airway management, tracheal dilatation, general anesthesia, respiratory failure, Klebsiella pneumoniae, case report