Characterization of malignant ovarian mass on [18F]FDG PET/CT: using metabolic indices and degree of solidity.

Background: The utility of [18F]FDG PET/CT for characterizing malignant ovarian mass has not been extensively studied. Here, we investigated various parameters that could be useful to differentiate malignant ovarian mass.

Methods: We enrolled 51 female patients (53.4±15.0 years), with 86 ovarian masses, who underwent pretreatment [18F]FDG PET/CT. Thirty six lesions were histopathologically confirmed with ovarian serous adenocarcinoma. Thirty one ovarian masses from gastric cancer and 19 masses from colorectal cancer were diagnosed by histopathological study or clinical follow-up. Ovarian masses were evaluated by size, solidity, and metabolic indices. The degree of solidity was scored from 1 to 5 according to the portion of solid and cyst. Metabolic activity was scored to be either positive (≥ liver) or negative (< liver). SUVmax (SUVovary) and the ratio of SUVmax of ovary to SUVmean of the liver (ovary/L ratio) were performed. Age, bilaterality and level of CA 125 were also compared. In statistical analysis, categorical variables were analyzed using Pearson's chi-square test, while continuous variables were evaluated either independent student's t-test or Mann-Whitney Test. Receiveroperating-characteristic analysis was used to obtain optimal cutoff values.

Results: Serous adenocarcinoma had significantly higher score in all metabolic indices over metastasis. However, there were no differences in all metabolic indices in ovarian metastasis. In contrast, solidity was different between metastatic mass from gastric and colorectal cancer. Ovarian metastasis from gastric cancer was significantly solid compared with that from colorectal cancer. In comparison of all three masses, solidity and all metabolic indices were significantly different. Patients with serous adenocarcinoma were older and had higher CA-125 level. Between metastases from gastric and colorectal cancer, there were no differences in age, bilaterality and CA-125.

Conclusions: Metabolic indices such as SUVovary and ovary/L ratio could be useful to differentiate serous adenocarcinoma from metastasis. Furthermore, the degree of solidity could play a role in predicting the origin of metastasis.