The value of 18F-FDG PET/MR in the metastasis and re-stage of melanoma after operation

Introduction: To investigate the value of 18F-FDG PET/MR whole-body imaging in the metastasis and re-phase of melanoma after operation.

Methods: The clinical data of 56 patients with melanoma after operation were retrospectively analyzed, and the PET/MR manifestations were analyzed. The PET/MR staging was compared with the traditional clinical staging based on CT and MR, and the difference between the detection rate and re-stage of metastatic lesions after operation was compared. The TNM staging standard of the United States Joint Commission on Cancer (AJCC) (Phase I - IV) was used for diagnosis. The gold standard is clinical and pathological diagnosis.

Results: Of 56 patients with melanoma after operation, 39 cases were found to have regional lymph node metastasis (N stage), a total of 128 lesions; There were 28 cases of distant metastasis (M stage), 194 lesions in total, including 35 lung metastasis, 41 liver metastasis, 17 brain metastasis, 76 bone metastasis, and 25 lymph nodes. The detection rate of regional lymph nodes by PET/MR was the same as that by conventional imaging (CT and MR) (98.4%), and the diagnostic coincidence rate of PET/MR was 97.6% higher than that of CT and MR (89.4%), with no statistical difference (P>0.05). Compared with conventional imaging (CT and MR), PET/MR found 69 more distant metastatic lesions in 28 patients, with significant statistical difference(P<0.05).Among them, 65 lesions were positive for PET-MR, negative for CT, and partial positive for MR, including 8 brain metastases, 22 liver metastases, 4 pancreas, 19 bones, 10 soft tissues, 2 lymph nodes, and 4 lesions were negative for PET uptake, but MR diagnosis was metastasis, including 1 brain metastasis, 1 liver metastasis, and 2 bone metastasis. The coincidence rate of PET/MR and MR diagnosis was 100% and 81%, respectively, with statistically significant difference (P<0.05).The detection rate and diagnostic coincidence rate of PET/MR in liver, brain, bone, muscle and soft tissue metastasis were higher than those of traditional CT and MR, with statistical significance (P<0.05). Compared with PET/MR, CT found 17 more lesions with significant statistical difference (P<0.01). Through PET/MR examination, a total of 17 patients changed the traditional clinical stage, with significant statistical difference (P<0.05) .Among them, 8 patients increased from stage I to stage III, 3 patients increased from stage II to stage IV, and 6 patients increased from stage III to stage IV.

Conclusions: 18F-FDG PET/MR is of high value for the metastasis and re-stage of melanoma after operation. The detection rate and accuracy of liver, brain, bone and soft tissue metastasis are higher than those of CT and MR, and lung lesions still need CT assistance diagnosis.