Occult myofibroblastic sarcoma detected on FDG-PET performed for cancer screening.

We present a rare case of occult low-grade myofibroblastic sarcoma (LGMFS) detected by marked 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) uptake on positron emission tomography (PET). A 46-year-old woman presented with abnormal FDG uptake in her back when FDG-PET was performed for cancer screening. The maximum standard uptake values (SUVmax) were 9.8. Physical examination and laboratory investigations revealed no abnormalities. Magnetic resonance images demonstrated an ill-defined 2 x 3 cm mass in the multifidus muscle. Excisional biopsy led to a pathological diagnosis of LGMFS. Additional wide resection was performed for local control. No local recurrence or distant metastasis was observed 12 months after the initial operation. This is the first report describing FDG-PET findings of LGMFS, suggesting a discrepancy between histological grade and SUV intensity in this low-grade entity.