To investigate the supplementary roles of MRI in the diagnosis of fetal abnormalities in twin fetuses.

MRI manifestations of 22 twins were retrospectively analyzed after abnormalities were found by prenatal ultrasonography (US) from Sep 2005 to Dec 2012. Two rapid scanning sequences were used in the study, fast-imaging employing steady-state acquisition (FIESTA) and fast inversion recovery motion insensitive (FIRM). MRI findings were compared with those of prenatal US, induced labour or postpartum diagnosis.

A total of 22 twins were reported with 23 abnormal fetuses in 20 twins and 2 normal twins. MRI confirmed central nervous system abnormalities in 3 abnormal fetuses which were anencephalus, meningoencephalocele and enlargement of lateral ventricles respectively. The case of meningoencephalocele was showed brain tissue protruding from the occipital defect on MRI, which was misdiagnosed as a cystic lymphagioma by US. The MRI diagnosis of anencephalus and enlarged lateral ventricles were accordant with US. MRI made the definite diagnosis in 5 chest abnormalities, which were left congenital diaphragmatic hernia (CDH) in 5 abnormal fetuses. They were diagnosed as possible CDH by US. Abdominal abnormalities (n=7, 8 abnormal fetuses) included two fetuses in one twin with expanded digestive tract, one fetus with expanded colon and rectus and five fetuses with omphalocele. MRI diagnosis was compatible with US diagnosis in the 7 cases. Twins micromelia were found in one case with 2 abnormal fetuses. Conjoined twins in chest and abdomen were found in another case, which manifested as two hearts, one shared liver and independent urinary tracts and gastrointestinal tracts on MRI. One fetus in twin was dead (n=1, 1 abnormal fetus). MRI showed small size and skin edema of the dead fetus. One acephalus acardius of twins (n=2, 2 abnormal fetuses) was proved. Normal MRI manifestations were indicated in 2 cases which were suspected by US for abnormal digestive tract and cryptorachischisis respectively.

MRI, an important supplementary method of prenatal US diagnosis, shows valuable advantages including multi-plane manifestations, more extensive visual field and good soft tissue contrast. It is especially helpful in the diagnosis and treatment of multiple pregnancy.

Diseases in twins; Magnetic resonance image; Ultrasonography; Prenatal diagnosis