AJR Teaching File: Pregnant Woman With Vaginal Spotting, Nausea, and Vomiting

Abstract

Pelvic ultrasound showed a normal-appearing intrauterine gestational sac in the right side of the endometrial cavity with an anterior placenta. Fetal crown–rump length was 3.44 cm, which is consistent with a gestational age of 10 weeks 3 days. Fetal cardiac motion was documented. In the left side of the endometrial cavity, a large predominantly echogenic mass with numerous subcentimeter cystic spaces measuring 9.8 × 9.3 × 11 cm was visible (Figs. 1A and 1B). MRI of the pelvis was performed without gadolinium. Sagittal and transverse single-shot fast spin-echo images and transverse T1-weighted images showed a gestational sac in the right anterior side of the endometrial cavity with an anterolateral placenta. A large heterogeneous mass with numerous subcentimeter cystic spaces filled the left posterior side of the endometrial cavity. A focal ovoid area of abnormal signal was visible in the anterior aspect of the mass. This area was hypointense on the single-shot fast spin-echo images and was heterogeneously hyperintense on the T1-weighted images (Figs. 1C–1F). Differential Diagnosis The differential diagnosis includes a singleton partial molar pregnancy or a twin gestation consisting of one normal pregnancy on the right side and an abnormal pregnancy on the left side with the differential diagnosis for the left-sided abnormal pregnancy including a partial or complete molar pregnancy, invasive mole (chorioadenoma destruens), and choriocarcinoma. Although placental abruption and degenerated uterine fibroids may also be included in the differential diagnosis for vaginal bleeding during pregnancy, placental abruption seems highly unlikely in this patient in light of imaging findings that are not consistent with hematoma and first trimester presentation. Degenerating fibroids also seem unlikely because the abnormal vascular mass is clearly endometrial. Diagnosis The diagnosis is twin gestation consisting of a normal pregnancy on the right side and a complete molar pregnancy on the left side. The patient elected to terminate the pregnancy and underwent a successful dilatation and curettage 2 days after initial presentation. Microscopic and genetic evaluation was compatible with a diagnosis of a twin gestation with an apparently healthy fetus, indicated by the presence of normal fetal lung tissue, and a coexistent complete hydatidiform mole.