A 20-year-old man presented with mild dyspnea and was diagnosed with a common cold at the first visit to a clinic. However, severe dyspnea persisted after 3 days. Enhanced computed tomography (CT) scan revealed a mediastinal mass in the subcarinal space, which compressed the right pulmonary artery and a delayed right pulmonary vein and airway enhancement at the tracheal bifurcation (-A, B). The mass was diagnosed as a mediastinal cyst and bronchoscopy was attempted; however, the patient was unable to be placed in the supine position due to severe respiratory distress. The patient was then transported to our hospital by ambulance due to the need for emergent surgery. Despite the fact that transportation took only two hours, his white blood cell count increased rapidly and symptoms became progressively worse, which suggested that the patient’s condition was emergent. Signed consent was obtained for all procedures. To ensure that the mass was a simple cyst without septum and mural nodule, magnetic resonance imaging (MRI) was performed as the patient’s condition allowed; the image showed a two-layered simple cyst, which indicated an infection or bleeding inside the cyst (-C, D). Since the symptoms developed and exacerbated rapidly, we performed emergent surgery. After the induction of general anesthesia with “stand-by” extracorporeal membrane oxygenation, video-assisted thoracic surgery (VATS) was performed. First, we punctured the cyst and aspirated white pus; then, we performed cyst wall fenestration on the subcarinal lesion and superior mediastinum. The bottom layer fluid inside the cyst contained both pus and blood, which were compatible with MRI findings, while continuous bleeding from the cyst wall was not observed (). Performing complete cyst resection was difficult owing to severe adhesion of the cyst to surrounding organs such as both main bronchi and pericardium. After surgery, the symptoms resolved immediately and completely. The postoperative course was uneventful and the patient was discharged on the 15th postoperative day. Pathological examination of the cyst wall revealed an inflamed bronchogenic cyst with the findings of bronchial gland, cartilage with infiltration of inflammatory cells, and no malignancy (). Six months after the operation, no sign of recurrence was observed.