Episternal Ossicles

Episternal ossicles are accessory bones that are located posterior or cephalad to the manubrium. They result from supernumerary ossification centers and are seen in less than ~2% of the population.

They range in diameter from 2 mm – 15 mm and are hard to see on radiographs. Cross sectional imaging reveals unilateral or bilateral triangular ossicles in a retro- or supra-manubrial location. In three dimensions, they are quadrilateral pyramids whose bases articulate with the manubrium. The apices point medially, but rounding of the corners may mask this appearance.
Recognition is important to differentiate them from calcified lymph nodes, fracture fragments, vascular calcifications, and foreign bodies.

References

• Restrepo CS, Martinez S, Lemos DF, Washington L, McAdams HP, Vargas D, Lemos JA, Carrillo JA, Diethelm L. Imaging appearances of the sternum and sternoclavicular joints. Radiographics. 2009 May-Jun;29(3):839-59.
• Stark P, Watkins GE, Hildebrandt-Stark HE, Dunbar RD. Episternal ossicles. Radiology. 1987 Oct;165(1):143-4.