Patient Repositioning Reveals a Malignant Pleura Effusion Initially Mistaken as a Bone Metastasis on 18FDG PET/CT.

A 70-year-old woman with breast cancer underwent F-FDG PET/CT for restaging. An FDG-avid focus corresponding to a rib on CT images was identified and interpreted as suggestive of an osseous metastasis. A PET/CT-guided biopsy was planned with the patient in prone position. Prone images demonstrated the FDG focus "moved" to the anterior chest and corresponding to pleural fluid. The diagnosis was altered from osseous metastases to pleural malignancy, and the bone biopsy was not performed. This case not only emphasizes the sensitivity of PET in the detection of malignancy, but also highlights the difficulty localizing small, mobile, FDG-avid foci.