Role of 18F-FDG PET/CT in differentiation of a benign lesion and metastasis on the ribs of cancer patients

Incidental 18-Fluoro-2-deoxyglucose positron emission tomography (18F-FDG) uptake in the ribs is a relatively common finding on positron emission tomography/computed tomography (PET/CT) images of cancer patients. This study examined the role of 18F-FDG PET/CT in differentiating between benign lesions and metastases on the ribs. This study included 264 lesions in 172 PET/CT cases with underlying malignancy showing newly developed indeterminate 18F-FDG rib uptake between June 2009 and May 2010. Patients with more than five FDG rib uptakes or hematologic malignancy were excluded. Malignancy was confirmed either histologically or by imaging studies, and clinical follow-up with serial images was at least 6months. The maximum standardized uptake value (SUVmax) of the rib lesion was recorded. The FDG uptake patterns (focal or segmental; discrete or non-discrete) and CT findings (evidence of fracture, soft tissue lesions, osteoblastic and/or osteolytic lesions) were recorded. There were 206 benign lesions and 58 metastases. The SUVmax was significantly higher in the metastatic group (3.0±1.8) than in the benign group (2.5±1.1), (P=.014). For the differential diagnosis between benign and metastatic lesions, the best SUVmax cut-off was determined to be 2.4. Significant indicators for metastasis were a segmental FDG uptake pattern (OR=10.262, 95% CI 4.151–25.371), presence of an osteoblastic/-lytic lesion (OR=22.903, 95% CI 10.468 to 50.108) and the absence of fractures on CT (OR=291.629, 95% CI 39.09–2175.666). SUVmax alone is not sufficient to differentiate benign and metastatic rib lesions in cancer patients. The diagnostic accuracy can be further increased when findings of the CT part of PET/CT are considered.