Diagnosis: Rounded atelectasis (benign)
Description and Key Points: This 70 year-old male underwent CT pulmonary angiogram performed to exclude pulmonary embolus. The above image windowed for lung shows a pleural-based area of atelectasis with a rounded outline, and with vessels curving towards and into it (the parachute sign, or comet-tail sign). There is adjacent pleural thickening.
Rounded atelectasis is associated with pleural disease, and is common in asbestos exposure. Typically areas measure 2-5cm in diameter. It is most common in the posterior lower lobes. It may have either acute or obtuse angles where it contacts the pleura. When it has the typical imaging appearance and location, a diagnosis can be confidently made. Bronchogenic carcinoma needs to be excluded in atypical cases. Follow-up CT, fine needle biopsy and PET scan are all options for further investigating atypical cases.
Reference: Webb WR, Higgins CB. Thoracic Imaging. Lippincott, Williams & Wilkins 2005.
Credit: Dr Laughlin Dawes