Purpose or Case Report: Twin molar pregnancy featuring a complete hydatidiform mole and a coexisting live fetus is a rare but important condition with unique imaging findings. A 24-year-old pregnant female presented for concern for molar pregnancy on ultrasound at an outside facility. The gestational age of the pregnancy at presentation was 22 weeks and 6 days. MRI was obtained which revealed a single living fetus in cephalic presentation. Along the anterior and left lateral uterine body/fundus was a large lesion with multiple small discrete T2 hyperintense cysts intermixed with more solid T2 isointense components, as well as T2 hypointense, T1 hyperintense foci consistent with hemorrhagic products. The lesion was distinct and did not arise from the placenta. Same day ultrasound revealed a “snowstorm” appearance, consistent with twin molar pregnancy with a complete hydatidiform form and coexistent live fetus.
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Conclusions: The incidence of twin molar pregnancy featuring a complete hydatidiform mole and coexisting live fetus is reported at 1 in 22,000 to 100,000 pregnancies. The etiology is thought to arise from two separate fertilization events, and it poses unique challenges in management and prognosis due to the co-occurrence of a viable fetus and the abnormal molar proliferation. Timely diagnosis is crucial, and imaging modalities such as ultrasound and magnetic resonance imaging (MRI) are essential tools in this process. The main imaging technique is ultrasound, which typically reveals a "snowstorm" or "grape-like" appearance characteristic of the molar component, which represents a mass of cystic spaces without a fetal pole, alongside a separate, normal-appearing gestational sac with a live fetus. MRI complements ultrasound by providing better soft tissue contrast and detailed anatomical information. On MRI, the molar component appears as a heterogeneous mass with high signal intensity on T2-weighted images due to its cystic structure, whereas the live fetus and its associated structures remain morphologically distinct. MRI is also valuable in assessing the extent of disease and invasive potential. The outcomes in twin molar pregnancies depend on the early detection and careful management of complications such as preeclampsia, hyperthyroidism, and the potential development of gestational trophoblastic neoplasia (GTN). While the risk of miscarriage, preterm birth, and maternal morbidity is elevated, successful continuation of pregnancy with a live birth is possible in selected cases.