IntroductionMassive ovarian edema (MOE) is a rare disease and few reports have described the magnetic resonance (MR) imaging manifestations in pregnancy.Case descriptionWe report here a case of MOE in a patient at 12 weeks’ gestation. Abdominal T2-weighted MR images showed asymmetric ovarian enlargement in a teardrop configuration, hyperintense peripherally displaced follicles, and twisting of the vascular pedicle between the enlarged ovary and uterus. The diagnosis of MOE due to ovarian torsion was confirmed by exploratory laparotomy. Preoperative imaging, especially the MR imaging could distinguish MOE from other conditions and demonstrate the relations of adjunct organ, and allowed for untwisting during laparotomy with successful preservation of the ovary.Discussion and evaluationUltrasonography is important in detecting, evaluating, and determining the malignant potential of adnexal masses in pregnancy, but its findings may be nonspecific and then MR may assist characterization. This case was tentatively diagnosed as typical MOE by preoperative imaging, but the shape and location of the hugely enlarged ovarian mass suggested torsion of the ovarian pedicle. In our case, the diagnosis was confirmed by exploratory laparotomy and the pedicle was successfully untwisted.ConclusionMR imaging proved useful for decisions on expectant management of MOE in pregnancy, and the patient’s affected ovary could be preserved.