A 26 year-old male with acute alcohol intoxication presents to the emergency department with complaints of substernal chest discomfort which is made worse with deep inspiration. The symptoms began 1 hour ago after three episodes of vomiting. His vital signs and ECG are unremarkable. He has no cardiac risk factors and is PERC negative (pulmonary embolism rule-out criteria). He has no past medical or surgical history. His physical exam is unremarkable with clear lungs bilaterally.
You obtain a chest x-ray.
1. What abnormality is seen?
2. What is this radiological sign called?
3. What is the possible diagnosis?