An Unusual Bone Metastasis Mimicking SAPHO (Synovitis, Acne, Pustulosis, Hyperostosis, and Osteitis) Syndrome on Bone Scintigraphy.

The costosternoclavicular region is not a common bone metastasis site, and symmetrical involvement is even rarer. Increased tracer uptake in the manubrium and sternoclavicular joints usually gives the typical "bull-horn" appearance seen in SAPHO syndrome (synovitis, acne, pustulosis, hyperostosis, and osteitis). Herein, we report a case of a 47-year-old woman with a history of invasive ductal carcinoma who had undergone left radical mastectomy 3 years earlier and presented with typical increased tracer uptake in the bilateral sternocostoclavicular region resembling the so-called bull horn. The final diagnosis of metastasis from breast cancer was made histopathologically following biopsy.