Foreign body granulomas typically present as a tender mass .
Granulatmous reactions aim to either resorb organic (e.g. wood,) or sequester inorganic (e.g. metal, glass) foreign bodies. If the foreign body completely resorbed the granulomatous reaction ceases but if not a capsule forms around the foreign body with the immune reaction often becoming inactive. If there is damage to the capsule then the granulomatous reaction, and possibly symptoms, recurs .
Lesion morphology can vary widely and depends on the material, size and location of the foreign body .
High frequency (>10 MHz) linear probe is useful :
- foreign bodies typically appear echogenic with posterior acoustic shadowing
- foreign body granuloma appears as a hypoechoic halo that can consist of hematoma, edema and/or granulation tissue
A long-standing foreign body granuloma will have a capsule with the following signal characteristics :
- T1: low signal
- T2: low signal
- T1C+: linear enhancement
- foreign body granulomas have been misdiagnosed as soft tissue tumors when a foreign body is not seen or recognized
- aggressive granulomatosis post hip replacement