The sternum (breast bone) may not have completely healed. If it skin related to the area in question, it could be a serious complication indicating infection. However bone (sternum) growth on the other hand takes many months and is not generally cause for concern.
The ultrasound imaging should have ruled out an abnormality that is solid (which may be a non-cancerous lump of tissue or a cancerous tumor) or fluid-filled (such as a benign cyst) or both cystic and solid. Ultrasound can also help show additional features of the abnormal area.
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