A case of torsion of a normal ovary in the third trimester of pregnancy: MRI findings with emphasis on asymmetry in the diameter of the ovarian veins

A 33-year-old woman, gravida two para one, at 31 weeks of gestational age experienced sudden onset of left lower quadrant pain and underwent unenhanced pelvic MRI. On fast imaging employing steady state precession (FIESTA) sequence images, a marked difference was observed in the diameters of the right and left ovarian veins. The right ovarian vein was torturous and dilated, measuring 35 mm in diameter, while the left ovarian vein was thin and linear, measuring 7 mm in diameter. The left ovary showed no apparent swelling or hemorrhage, but was suspected to have been shifted anteriorly. The patient underwent explorative laparotomy and was found to have left ovarian torsion. A difference in diameter of the ovarian veins, with thinning of the twisted side and compensatory dilatation of the contralateral side for drainage of increased uterine blood flow, may be a useful imaging sign for the diagnosis of ovarian torsion during pregnancy.