Objectives: The objectives of this study were to correlate fluorodeoxyglucose uptake in ovarian masses on positron emission tomography/computed tomography (PET/CT) with pathological grades of malignancy and subtypes and to determine the appropriate approach for combining PET/CT and contrast-enhanced magnetic resonance imaging (CE-MRI) to characterize ovarian masses.
Materials and methods: A retrospective study was conducted including 127 patients who underwent surgical resection of an ovarian mass (30 benign, 31 borderline, 66 malignant). Maximum standardized uptake values (SUVmax) obtained with PET/CT were compared between pathological grades of malignancy and subtypes. Two radiologists each independently conducted a blind evaluation of CE-MRI for all lesions and classified them by the grade of malignancy as determinate (benign, borderline, or malignant) or indeterminate and by subtype as mucinous or nonmucinous. The appropriate approach for combining CE-MRI and PET/CT was determined by comparing the combined diagnostic ability with that of CE-MRI alone.
Results: The SUVmax of malignant tumors was significantly higher than that of benign and borderline lesions (mean, 7.8, 1.7, 2.4; P < 0.05). Among malignant tumors, SUVmax was significantly lower in mucinous adenocarcinomas compared with nonmucinous malignant tumors (mean, 3.3, 8.4; P < 0.05) and lower in clear cell adenocarcinomas compared with other subtypes of nonmucinous malignant tumors (mean, 6.0, 9.4; P < 0.05). The SUVmax cutoff that best differentiated malignant lesions from benign/borderline lesions was 2.4 for mucinous and 4.0 for nonmucinous tumors. These cutoffs correctly classified lesions as malignant or not in 88.2% of cases (112/127). When PET/CT was combined with CE-MRI, the readers correctly classified 85% (34/40) and 86.5% (32/37) of indeterminate lesions on CE-MRI. However, PET/CT was not useful for classifying determinate lesions on CE-MRI, particularly because PET/CT correctly classified only 70.1% (12/17) of clear cell adenocarcinomas, whereas CE-MRI alone correctly classified 94.1% (1617). Thus, compared with CE-MRI alone, the diagnostic accuracy of CE-MRI + PET/CT when PET/CT was added only for indeterminate lesions on CE-MRI was significantly higher for both readers for differentiating between benign and borderline/malignant (P < 0.05), as well as between benign/borderline and malignant (P < 0.01).
Conclusion: Fluorodeoxyglucose uptake in ovarian masses correlates with pathological subtypes as well as the grade of malignancy. Furthermore, the combination of CE-MRI and PET/CT is a highly accurate method for characterizing ovarian masses because PET/CT can be used as a complement to classify indeterminate lesions as malignant or not based on appropriate cutoff SUVmax for mucinous and nonmucinous tumors.