LAUSR

© BMJ Publishing Group Limited 2021. No commercial reuse. See rights and permissions. Published by BMJ. DESCRIPTION A 23yearold woman with a history of cannabinoid hyperemesis syndrome (CHS) presented with multiple episodes of nonbilious, nonbloody vomiting. She reported a 3year history of daily marijuana use. Unlike her prior presentations characterised by nausea and vomiting, the patient endorsed ongoing cramping chest pain with difficulty breathing. The patient continued to endorse chest pain with epigastric discomfort nonresponsive to analgesia and antiemetics, despite resolution of vomiting. ECG revealed sinus tachycardia of 108 bpm, which resolved with intravenous fluid volume repletion. The chest Xray was initially interpreted as within normal limits. With concern of her persisting epigastric discomfort a CT abdomen/pelvis was obtained to exclude an acute abdomen. Findings revealed a partially visualised trace pneumomediastinum. This prompted a secondlook of the initial chest Xray, which in retrospect had trace evidence of a pneumomediastinum (figure 1). Subsequent CT chest revealed an extensive pneumomediastinum with air tracking along the left hilum/bronchovascular sheath of an unclear source with no radiographic evidence of chest trauma (figure 2). A watersoluble contrast oesophagram had no evidence of oesophageal perforation, hence Boerhaave’s syndrome (spontaneous rupture of the oesophagus) was excluded (figure 3). Given her recurring cyclic vomiting in the setting of cannabis use, the patient was diagnosed with CHS with spontaneous pneumomediastinum (SPM). The patient was managed conservatively, with complete recovery. SPM or spontaneous mediastinal emphysema is a rare condition characterised by free air in the mediastinum not preceded by thoracic trauma, surgery or any other medical procedure. A classic clinical triad described consists of thoracic pain (usually retrosternal and pleuritic in nature), subcutaneous emphysema and dyspnoea. Inhaled marijuana use has been infrequently identified as a potential risk factor for the development of SPM. Weiss et al reported 14 cases of marijuana use associated with pneumomediastinum in a retrospective review. It is a selflimiting condition resulting from alveolar rupture secondary to an acute increase in intrathoracic pressure subsequently leading to dissection of air along the bronchovascular sheath towards the mediastinum. The hypothesised pathophysiology of marijuanarelated pneumomediastinum is barotrauma occurring during the breathing movements. An increase alveolar pressure gradient results in rupture of alveolar septa with air dissecting around the peribronchial and perivascular sheaths.