Companion shadows are smooth, homogeneous, radiopaque shadows running parallel along the bones. In a study of 700 chest radiographs, Ben Felson found that 75% had companion shadows on the lower ribs 3.
They appear secondary to soft tissues and intercostal muscles running along:
Companion shadows need to be differentiated from periosteal reactions secondary to adjacent bony or soft tissue pathology.
- 1. Kurihara Y, Yakushiji YK, Matsumoto J et-al. The ribs: anatomic and radiologic considerations. Radiographics. 1999;19 (1): 105-19. Radiographics (full text) - Pubmed citation
- 2. Hofer M. The Chest X-Ray. Thieme Medical Publishers. (2007) ISBN:1588905543. Read it at Google Books - Find it at Amazon
- 3. Felson B. Chest roentgenology. AITBS Publishers. (2018) ISBN 978-9374734872. https://www.amazon.co.uk/Chest-Roentgenology-Benjamin-Felson/dp/9374734877