Codman triangle

{{short description|New growth of bone following the raising of periosteum away from the bone}}

File:Codman triangle 2014-01-29 21-07.jpeg

The Codman triangle (previously referred to as Codman's triangle) is the triangular area of new subperiosteal bone that is created when a lesion, often a tumor, raises the periosteum away from the bone.{{Cite web |title=Codman's triangle - General Practice notebook |url=https://gpnotebook.com/simplepage.cfm?ID=-288358364 |access-date=2022-10-26 |website=gpnotebook.com |date=January 2018 |archive-date=2022-10-26 |archive-url=https://web.archive.org/web/20221026085815/https://gpnotebook.com/simplepage.cfm?ID=-288358364 |url-status=live }} A Codman triangle is not actually a full triangle. Instead, it is often a pseudotriangle on radiographic findings, with ossification on the original bone and one additional side of the triangle, which forms a two sided triangle with one open side. This two sided appearance is generated due to a tumor (or growth) that is growing at a rate which is faster than the periosteum can grow or expand, so instead of dimpling, the periosteum tears away and provides ossification on the second edge of the triangle.{{Cite web |title=Periosteal Reaction |url=https://rad.washington.edu/about-us/academic-sections/musculoskeletal-radiology/teaching-materials/online-musculoskeletal-radiology-book/periosteal-reaction/ |access-date=2022-10-26 |website=UW Radiology |language=en |archive-date=2022-10-26 |archive-url=https://web.archive.org/web/20221026085813/https://rad.washington.edu/about-us/academic-sections/musculoskeletal-radiology/teaching-materials/online-musculoskeletal-radiology-book/periosteal-reaction/ |url-status=live }} The advancing tumour displaces the periosteum away from the bone medulla. The displaced and now lateral periosteum attempts to regenerate underlying bone. This describes a periosteal reaction.{{cn|date=August 2021}}

The main causes for this sign are osteosarcoma, Ewing's sarcoma, eumycetoma, and a subperiosteal abscess.{{cite journal| pmid=8184073 | doi=10.1148/radiology.191.3.8184073 | volume=191 | title=Periosteal Ewing sarcoma | year=1994 |vauthors=Shapeero LG, Vanel D, Sundaram M, Ackerman LV, Wuisman P, Bauer TW, Neuenschwander S, Contesso G, Janney C, McDonald DJ| journal=Radiology | pages=825–31}}{{Cite journal |last=Hide |first=Geoff |date=April 19, 2018 |title=Imaging in Classic Osteosarcoma: Practice Essentials, Radiography, Computed Tomography |url=https://emedicine.medscape.com/article/393927-overview |journal= |website=Medscape |access-date=October 26, 2022 |archive-date=October 26, 2022 |archive-url=https://web.archive.org/web/20221026085804/https://emedicine.medscape.com/article/393927-overview |url-status=live }}