A diagnostic dilemma: Distinguishing gestational trophoblastic disease from scar ectopic pregnancy in a post-cesarean patient

A 26-year-old woman with two previous cesarean sections presented with amenorrhea and a positive urine pregnancy test. Ultrasound initially suggested scar ectopic pregnancy. However, MRI of the pelvis revealed a heterogeneously hyperintense lesion involving the endometrium and anterior myometrium, with multiple flow voids and no serosal invasion findings more consistent with gestational trophoblastic disease, her serum β-hCG was markedly elevated. She was started on a Methotrexate-Leucovorin protocol and responded well, with a steady fall in β-hCG and only mild side effects. This case highlights the diagnostic challenge of distinguishing between scar ectopic pregnancy and GTD in the absence of a visible gestational sac. Anchoring the diagnosis on scar pregnancy alone may delay appropriate evaluation. When myometrial vascularity is high and β-hCG is elevated, early MRI can help uncover GTD and guide timely management.