Inflammatory myofibroblastic tumor: FDG PET/CT findings with pathologic correlation.

Purpose: The aim of this study was to evaluate retrospectively F-FDG PET/CT findings of inflammatory myofibroblastic tumor (IMT) and their correlation with the pathologic findings.
Patients and Methods: FDG PET/CT findings were reviewed in 5 patients with IMT and 1 patient with spindle cell sarcoma transformed from IMT. PET/CT scans were performed in all 6 patients before surgery. Follow-up FDG PET/CT scan was performed in 1 patient. The location, size, maximal standardized uptake value (SUVmax), and pathologic findings of the tumors were reviewed. The correlation between the FDG uptake and pathologic findings were analyzed.
Results: A total of 10 lesions were detected in all 6 patients. The tumor locations were liver (n = 3), retroperitoneum (n = 2), spleen (n = 1), lung (n = 1), and bone (n = 3). Seven IMTs and 1 spindle cell sarcoma transformed from IMT were confirmed by pathology. The mean SUVmax of the pathologically proven tumors was 10.9 ± 5.5, with a high variability of SUVmax among tumors ranging from 3.3 to 20.8. The tumors (n = 7) with high cellularity had stronger FDG uptake, while the tumors (n = 1) with low cellularity had relatively low FDG uptake. The tumors with nuclear atypia and relatively high proliferative index had very strong FDG uptake, while those with low proliferative index or negative Ki-67 staining had relatively lower FDG uptake. One small tumor with abundant plasma cells showed high FDG uptake, while 1 large tumor with focal inflammatory cell infiltrate showed lower FDG uptake. One patient developed local recurrences and distant metastases revealed by the second FDG PET/CT scan 7 months after resection.
Conclusions: FDG uptake in IMTs varied from low to high FDG uptake, which may be due to tumor cellularity, biological behaviors of the tumor cells, the composition and the proportion of inflammatory cells, and the extent of activation of the inflammatory cells. FDG PET/CT may be useful for detection of the primary tumors, local recurrences, and distant metastases.