Aims: To describe the clinical and histological features of a series of cases of placentas originally diagnosed as partial moles in which the final diagnosis was that of placental stem villous hydrops, mesenchymal dysplasia or Beckwith-Wiedemann syndrome.
Methods and results: We searched a computerized database containing cases of suspected or proven trophoblastic disease examined at the Trophoblastic Disease Unit at Charing Cross Hospital, London, to identify cases in which stem vessel hydrops was present without other histological features of partial mole. For each case, histological sections were examined and the histological features present recorded. There were 15 cases identified. Placental weight was above the 95th centile of the normal for gestation in all cases in which this information was documented. In an additional five cases the placenta was described as 'large'. All cases had marked stem vessel hydropic change with cyst formation and in the majority of cases some terminal villous hydrops was also present. In 13 of the 15 cases there was marked aneurysmal dilatation of stem villous vessels. Nine had focal chorioangiomatoid change and in four of these extramedullary haematopoiesis was focally present in these areas. No excessive trophoblast proliferation was noted in any case and no trophoblastic inclusions typical of partial mole were identified.
Conclusions: This study has identified cases of stem villous hydrops, mesenchymal dysplasia or Beckwith-Wiedemann spectrum in pregnancies initially diagnosed as partial hydatidiform mole in the second half of pregnancy and has highlighted the need for detailed pathological examination and clinicopathological correlation in all such cases.