Mediastinal masses are uncommon and difficult to diagnose. Endoscopic ultrasound with fine-needle aspiration (EUS-FNA) is a minimally invasive technique for diagnosis of mediastinal lesions with few complications. Our report described a mediastinal bronchogenic cyst with soft tissue density infected by Streptococcus pyogenes (S. pyogenes) after EUS-FNA, accompanied by respiratory cardiac arrest and superior vena cava syndrome. The patient underwent cardiopulmonary resuscitation to gain the chance for emergency surgery and recovered. Clinicians should be aware that mediastinal mass with soft tissue density shown on imaging may be mediastinal cyst containing high density mucin, FNA should be avoided if cystic masses cannot be ruled out.© 2022 Published by Elsevier Ltd.