A rare case of pneumomediastinum caused by an endobronchial mass

SESSION TITLE: Medical Student/Resident Lung Pathology SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: October 18-21, 2020 INTRODUCTION: Pneumomediastinum is characterized by the abnormal presence of air in mediastinal tissue. The majority of cases of pneumomediastinum result from a benign etiology, and outcomes are good with supportive care and observation alone. However, in some cases additional work up and intervention is necessary. We present an unusual case of pneumomediastinum to highlight the pathophysiology and need for treatment. CASE PRESENTATION: A 35-year-old woman with metastatic colon cancer presented to the emergency department with substernal chest pain that radiated to her neck, hemoptysis, shortness of breath, and coughing episodes with “hissing sounds.” Chest computed tomography scan (CT) revealed multiple pulmonary metastatic lesions including a left lower lobe (LLL) endobronchial mass with distal LLL hyperinflation and pneumomediastinum. Fiberoptic bronchoscopy revealed a near complete obstructing mass at the orifice of the LLL that was acting as a one-way valve limiting air flow out of the lobe. She underwent bronchoscopic excision of the endobronchial mass and LLL bronchial stent placement to restore airway patency. Follow up CT showed resolution of LLL hyperinflation and pneumomediastinum. The patient was discharged in improved condition to follow up with medical and radiation oncology. DISCUSSION: Pneumomediastinum is rare, with a reported incidence of 1/44,500 adults treated in emergency departments.1 Patients classically present with a triad of dyspnea, thoracic pain, and sub-cutaneous emphysema.2 Pneumomediastinum is often benign, but rarely has the potential to develop tension physiology which may lead to hemodynamic collapse.3 It occurs as a result of malignancy, iatrogenic injury, blunt trauma, positive pressure ventilation, severe asthma exacerbation, and Valsalva maneuvers.4 Macklin proposed a pathophysiologic mechanism in 1944, now known as the Macklin effect, in which alveolar rupture releases air which travels to the mediastinum along the broncho-vascular sheaths.5 CONCLUSIONS: This case is unique in that pneumomediastinum is rarely associated with endobronchial masses. 6,7,8 When seen, it is often difficult to directly associate the lesion with diagnosis. Other reported cases have focused on bronchial invasion as the underlying pathophysiology of pneumomediastinum.7 In this case, there is documented hyperinflation distal to the endobronchial mass, as well as improvement in hyperinflation and pneumomediastinum after treatment. This provides strong evidence for the Macklin effect as the cause of pneumomediastinum. While pneumomediastinum is typically benign and self-limited, providers should be aware of potentially serious pathology requiring intervention. Reference #1: Russo A, Del Vecchio C, Zaottini A, et al. Role of emergency thoracic ultrasonography in spontaneous pneumomediastinum. Two case report. G Chir. 2012;33:285-296. Reference #2: Meireles J, Neves S, Castro A, França M. Spontaneous Pneumomediastinum Revisited. Respiratory Medicine CME 4. 2011;4:181–183. Sahni S, Verma S, Grullon J, et al. Spontaneous pneumomediastinum: time for consensus. N Am J Med Sci. 2013;5:460-464. Kouritas VK, Papagiannopoulos K, Lazaridis G, et al. Pneumomediastinum. J Thorac Dis. 2015;7(Suppl 1):S44–S49. Macklin MT, Macklin CC. Malignant interstitial emphysema of the lungs and mediastinum as an important occult complication in many respiratory diseases and other conditions: an interpretation of the clinical literature in the light of laboratory experiment. Medicine. 1944;23:281-358. Kim KI, Lee JW, Lee MK, Lee CH, and Park SK. Polypoid Endobronchial Hodgkin’s Disease with Pneumomediastinum. Br J Radiol. 1999;72(856): 392–394. Kim KS, Moon YK, Jeon HW, Park CB, Ahn MI, Lee KY, Park JK. Endobronchial Angiofibroma in the Aberrant Tracheal Bronchus Presenting as Spontaneous Pneumomediastinum. J Cardiothorac Surg. 2015;10(1):100. Zahid M, Shafiq I, Albon L, Kause J. Typical Bronchial Carcinoid Tumour Presenting as Pneumomediastinum. BMJ Case Rep. 2011;2011:bcr0120113744. DISCLOSURES: No relevant relationships by Rage Geringer, source=Web Response No relevant relationships by Patrick Jenkins, source=Web Response No relevant relationships by Chakradhar Kotaru, source=Web Response