An acardiac twin with advanced brain development and a minor form of holoprosencephaly and intracerebral retina-like pigmented tissue: a case report and review of the literature

Hypothesized pathogenesis of acardius acephalus, acormus, amorphus, anceps, acardiac edema, single umbilical artery, and pump twin risk prediction

Background

Acardiac twinning complicates monochorionic twin pregnancies in ≈2.6%, in which arterioarterial (AA) and venovenous placental anastomoses cause a reverse circulation between prepump and preacardiac embryos and cessation of cardiac function in the preacardiac. Literature suggested four acardiac body morphologies in which select (groups of) organs fail to develop, deteriorate, or become abnormal: acephalus (≈64%, [almost] no head, part of body, legs), amorphus (≈22%, amorphous tissue lump), anceps (≈10%, cranial bones, well‐developed), and acormus (≈4%, head only). We sought to develop hypotheses that could explain acardiac pathogenesis, its progression, and develop methods for clinical testing.

Methods

We used qualitatively described pathophysiology during development, including twin‐specific AA and Hyrtl's anastomoses, the short umbilical cord syndrome, high capillary permeability, properties of spontaneous aborted embryos, and Pump/Acardiac umbilical venous diameter (UVD) ratios.

Results

We propose that each body morphology has a specific pathophysiologic pathway. An acephalus acardius may be larger than an anceps, verifiable from UVD ratio measurements. A single umbilical artery develops when one artery, unconnected to the AA, vanishes due to flow reduction by Hyrtl's anastomotic resistance. Acardiac edema may result from acardiac body hypoxemia combined with physiological high fetal capillary permeability, high interstitial compliance and low albumin synthesis. Morphological changes may occur after acardiac onset. Pump twin risk follows from UVD ratios.

Conclusion

Our suggested outcomes agree reasonably well with reported onset, incidence, and progression of acardiac morphologies. Guidance for clinical prediction and testing requires ultrasound anatomy/circulation study, from the first trimester onward.

Facets of Clinical Appearance and Aetiology in an Unusual Bovine Amorphus Globosus

Amorphus globosus is a rare entity, more common in the cow but also reported in mares, buffaloes and goats. In respect of both development and clinical presentation, this abnormity can be evolved very variably. Previously, it has been discussed whether it is a form of twin pregnancy or placental teratoma. This case report deals with morphology and genetic observations in an unusual bovine amorphus globosus exhibiting a rudimentary clitoris and vulva, gut-like structures and rudimentary bones. The amorphus globosus was shown to be dizygotic to the normal male twin using the BovineSNP50 v2 BeadChip and had a genetical female sex. Aspects of aetiology and pathogenesis as well as the possible impact of amorphus globosus in the emergence of freemartinism are discussed.