- This case report describes a twin fetus diagnosed in the third trimester with an enlarging abdominal mass that was confirmed on fetal magnetic resonance imaging (MRI) to be a hepatic mesenchymal hamartoma (HMH) without involvement of the placenta. Serial ultrasonography demonstrated progressive enlargement of the mass and infant was delivered at 33 + 6 weeks gestational age following maternal complications. On the fifth day, at laparotomy, a huge mass connected to the lower portion of the liver was completely resected. Microscopic evaluation confirmed a hepatic mesenchymal hamartoma. Postoperative recovery was uneventful and the infant was discharged at 4 weeks. The antenatal diagnosis of the hepatic mesenchymal hamartoma by fetal MRI and subsequent follow-up by serial ultrasonography emphasizes the importance of combining these 2 modalities for optimal management of the pregnancy to allow a favorable outcome.