Fetal hamartoma constitutes a rare benign lesion of the mesenchymal tissue. We describe here the antenatal diagnosis and management of a giant hepatic mesenchymal hamartoma in conjunction with placental mesenchymal dysplasia.
A 29-year-old woman, gravida 2 para 1, was referred to our tertiary center at 13 + 3 weeks' gestation because of a large space-occupying lesion arising from a multiloculated placenta. The initial sonographic findings were suspicious for a partial hydatidiform placenta in addition to a stalked hypoechogenic round structure connected to the placenta, consistent with a placental chorangioma. Maternal β-human chorionic gonadotropin (β-hCG) and alpha fetoprotein (AFP) levels were within normal ranges. The fetus showed normal biometric measurements. Nuchal translucency screening revealed a risk of 1 in 2959 for trisomy 21. Biweekly follow-up scans were performed. At 20 weeks, targeted ultrasound revealed a hypoechogenic infradiaphragmatic cystic mass (Figure 1). The lesion measured 19 × 17 × 19 mm and showed marked septation and rapid growth, reaching a size of 74 × 47 × 50 mm by 23 weeks without measurable perfusion (Figure 2). At this time the diagnosis of a large progredient hamartoma was assumed. At 27 + 4 weeks inpatient admission was necessary because of preterm labor, prompting an immediate Cesarean section. Preoperative ultrasound showed continuing growth of the hepatic mass to 98 × 73 × 86 mm. A premature female infant was delivered weighing 1452 g, with Apgar scores of 5 and 8 at 5 and 10 min, respectively. The infant was immediately admitted to the neonatal unit in good general condition.
Repeat abdominal punctures of the cystic lesion were performed for decompression and optimization of pulmonary function (removal of a total of 760 mL of clear fluid). The mass subsequently decreased in size, leaving an echogenic area in the left hepatic lobe. Gross inspection showed a huge jelly-like placenta with multiple cysts, as seen prenatally. Histopathological findings and immunohistochemistry were consistent with placental mesenchymal dysplasia (PMD) (Figure 3).
Several terms have been used in previously published reports that allude to the same placental condition, such as mesenchymal stem villous hyperplasia or pseudopartial mole1, 2. However, the main characteristic finding, apart from enlarged dysplastic villi with myxoid stroma, is the absence of abnormal trophoblast proliferation in contrast to hydatidiform mole.
The differential diagnosis of PMD and its postpartum confirmation is of particular importance, as it might mimic a molar placenta. This placental anomaly is potentially associated with an adverse pregnancy outcome, including intrauterine growth restriction, fetal demise and neonatal death. Recent reports suggest a female : male ratio of PMD of 4:13. The vascular endothelial growth factor-D, which has been mapped to Xp22.31, may play a key role3, 4. According to Vaisbuch et al.2 fetal outcome depends on the relative size and growth of the remaining functional placenta. In the present case close follow-up revealed appropriate growth of the normal part of the placenta.
Occasionally PMD is associated with placental and/or fetal hamartoma5. It has been suggested that continuous inadequate blood supply may cause aneurysmal dilation of the chorionic vessels and hyperplasia of placental stem villi. Secondary to the placental changes, ischemic lesions of the fetal liver occur, finally resulting in large progredient cystic masses. To date, only five similar cases with PMD and fetal abdominal masses, later confirmed as hepatic hamartoma, have been documented3, 6–9. Differential diagnoses to be considered include hepatic lymphangioma, hemangioepithelioma and hepatoblastoma. The treatment of hamartoma encompasses percutaneous cyst aspiration (either pre- or postnatally) or definitive surgical intervention in the postnatal period (enucleation, lobectomy). Although cases with antenatally detected hamartoma carry a poor prognosis, successful conservative approaches and spontaneous regression have also been observed, thereby frequently resulting in intrahepatic calcifications, as seen in our case10, 11.
The paucity of antenatal data and the frequent underdiagnosis of PMD underline the diagnostic dilemma, as the definitive diagnosis of partial mole or mesenchymal dysplasia of the placenta can only be established during pathologic examination.
Detailed anatomic survey and serial ultrasound examinations should be performed in order to detect fetal compromise and associated anomalies. A normal karyotype and moderate β-hCG and AFP levels should raise suspicion of PMD when a placental lesion is detected.