Granulomatous inflammation mimicking bone metastases on F18 FDG PET

Learning Objectives 1. Not all FDG avid skeletal lesions are malignant. 2. In special situations, confirmation of a bony metastasis may be valuable. 3. Granulomatous inflammation is a frequent mimicker of pathology on FDG PET in the bone and elsewhere.

We describe the case of a 53 yo female with T2N0 anal cancer who was found to have several FDG avid skeletal lesions. Biopsy of a right ischial lesion revealed non-necrotizing granulomas consistent with granulomatous inflammation, and no evidence of squamous cell carcinoma. Full evaluation for sarcoidosis or an infectious etiology was negative. We illustrate several unusual characteristics of granulomatous inflammation in our patient, which may be of value in daily clinical practice. Bone marrow/cortical bone involvement by granulomas is usually discovered mostly after patients become symptomatic - anemic -. In our patient bone marrow involvement was not clinically apparent and our PET scan uncovered it. In the era of PET scanning the rate of bone marrow and solid organ involvement of granulomatous diseases could be assessed with a better accuracy. FDG avid lesions in a patient known or at risk to have granulomatous disease should be evaluated carefully. The occasional association of granulomas and cancers in various organs also requires close attention when staging and restaging patients with FDG PET. Granulomatous diseases have also been reported to occasionally flare up following chemotherapy, which also occurred in our patient [1]. Referring clinicians and radiologists or nuclear medicine physicians should keep in mind that not all FDG avid skeletal lesions are malignant and biopsy of suspicious metastatic lesions should be contemplated in certain circumstances for accurate staging