Author’s reply re: Vesicular mole in a twin pregnancy
Sir,
We thank Tsz-Kin Lo for the interest in the
mini-commentary1,2. The issues raised by the author
are valid. Indeed, the purpose of the mini-commentary was to elaborate
on the similarities and differences between vesicular mole in a twin
pregnancy, placental mesenchymal dysplasia (PMD) and a partial vesicular
mole. The mini-commentary states that trophoblastic proliferation and
stromal inclusions are not seen in PMD, implying that the distinction is
possible only on pathology. I thank the author for making this explicit.
Histopathological diagnosis is unfortunately available only in
retrospect. The suggestion to consider amniocentesis for molecular
diagnosis of Beckwith-Wiedemann syndrome in a case of suspected complete
vesicular mole and an apparently normal fetus in a twin pregnancy
signals the challenges of antenatal diagnosis. Such a consideration
would be unnecessary if one were to be sure of the diagnosis without the
availability of placental histopathology.
Ultrasound is the most common modality for prenatal diagnosis of
vesicular mole in a twin pregnancy2. MRI has been
described for the detection of molar placenta and a sac separating from
fetus and normal placenta in a case of vesicular mole in a twin
pregnancy. This would be helpful to differentiate it from PMD or a
partial mole with a co-existing fetus. Another possibility is a
sub-chorionic haematoma, with which it is confused not
infrequently3. However, there are no studies that have
investigated the diagnostic accuracy of MR imaging compared to
ultrasound in complete vesicular mole with a co-existing
fetus4.
An international consensus statement reported that CVS cells might not
reflect the (epi)genetic constitution of the fetus, and therefore,
false-positive results might occur5. Hence,
amniocentesis is the more reliable investigation for imprinting
disorders such as Beckwith-Wiedemann syndrome.
The criticism of over-simplification/generalisation is accepted. The
intention was to state common associations and outcomes, not the
exceptional ones.
Amarnath Bhide
Fetal Medicine Unit
St George’s University Hospitals NHS Foundation Trust
London