Necrotic pseudotumor caused by a metal-on-metal total hip prosthesis: imaging characteristics on (18)F-FDG PET/CT and correlative imaging.

Necrotic pseudotumor is a complication of metal-on-metal arthroplasty that has been reported with increasing frequency in the last 5 years. It is believed to be the result of a hypersensitivity reaction to metal ions such as nickel, cobalt, or chromium that are released in large quantities from these prostheses. The imaging appearance of a necrotic pseudotumor caused by a metal-on-metal prosthesis, on (18)F-FDG PET/CT or (99m)Tc-MDP bone scan has not been previously described in the literature. Our case demonstrates that a necrotic pseudotumor can be detected incidentally in oncologic patients referred for an (18)F-FDG PET/CT or a (99m)Tc-MDP bone scan, and recognizing this process is vital in preventing further tissue necrosis and patient morbidity, as the offending prosthesis must be promptly removed. The imaging characteristics of a necrotic pseudotumor on PET/CT and bone scan may also mimic a malignant process such as a necrotic sarcoma, and can represent a potential pitfall leading to a false positive diagnosis in an oncologic patient.