A 22-year-old man presents with worsening shortness of breath on exertion. His past medical history reveals that he has had a dental extraction for a tooth abscess 4 months previously, and recalls feeling flu-like symptoms for 2–3 weeks afterwards but did not seek medical attention. His blood tests, including inflammatory markers, are normal. His scan is provided in Figures 17.1, 17.2 and 17.3 and Videos 17.1, 17.2, 17.3, 17.4, 17.5, 17.6, 17.7, 17.8, 17.9 and 17.10.