Acardiac fetuses (Amorphus globosus monsters)
Keywords: amorphous, globosus, (AG),(AGM), acardiac fetus (AF), bovine, placenta, monsters, karyotype, cattle
The essential nature of these fetuses is that they do not have hearts. Therefore the term amorphous globosus (AG) is less specific that acardiac fetus (AFs). AFs are placental parasites originating from embryos that do not develop into normal fetuses. Although the term "monster" is commonly applied to these fetuses because of their grotesque appearance, that term is melodramatic and archaic. Indeed. the term "monster" has been largely discarded in human medicine. The term anidian monster has also been used to describe an AF i.e. The cytological sex of a bovine anidian (amorphous) twin monster. HO Dunn et al. Cytogenetic and Genome Research, 1967. This term is seldom used and its etymology remains a mystery.
Should one consider amorphous globusus monsters (AFs) as fetuses? Merriam-Webster defines a fetus as: "An unborn or unhatched vertebrate especially after attaining the basic structural plan of its kind". On perusing descriptions of AFs it appears that they probably contain endoderm, ectoderm and mesoderm although these basic embryonic layers do not develop normally. If these three layers are considered to be a "basic structural plan" (could that not also be the DNA in a single cell?) then AFs should be referred to as fetuses.
Should one consider amorphous globusus monsters (AFs) as fetuses? Merriam-Webster defines a fetus as: "An unborn or unhatched vertebrate especially after attaining the basic structural plan of its kind". On perusing descriptions of AFs it appears that they probably contain endoderm, ectoderm and mesoderm although these basic embryonic layers do not develop normally. If these three layers are considered to be a "basic structural plan" (could that not also be the DNA in a single cell?) then AFs should be referred to as fetuses.
The image below shows an acardiac quadruplet born together with three normal triplets females also shown in another LORI entry.
Image size: 2816 x 2070 px
It would be convenient to assume that this AF was also a female because the triplet females were not androgenized (freemartins). However, the genital system of the acardiac fetus had not developed, therefore the possibility of it having an XY karyotype could not be discounted (see below).
Below, an AF and a radiograph of that fetus (inset). The radiograph shows a small center of mineralization/ossification. The umbilical cord has broken free of the host placenta.
Image size: 947 x 719 px
A radiograph of a bilobed acardiac fetus with a highly mineralized/ossified focus.
Image size: 1200 x 1039 px
Acardiac fetuses are most common in cattle, followed by the small ruminants, then horses and rarely, humans. The reason that they occur more frequently in cattle than other animals is probably because placental fusion and anastomosis of blood supply is very common in cattle, also explaining the high frequency of freemartins in these animals. Without a blood supply joined to that of a viable fetus (see below) an acardiac fetus can not survive.
Image size: 2816 x 2070 px
It would be convenient to assume that this AF was also a female because the triplet females were not androgenized (freemartins). However, the genital system of the acardiac fetus had not developed, therefore the possibility of it having an XY karyotype could not be discounted (see below).
Below, an AF and a radiograph of that fetus (inset). The radiograph shows a small center of mineralization/ossification. The umbilical cord has broken free of the host placenta.
Image size: 947 x 719 px
A radiograph of a bilobed acardiac fetus with a highly mineralized/ossified focus.
Image size: 1200 x 1039 px
Acardiac fetuses are most common in cattle, followed by the small ruminants, then horses and rarely, humans. The reason that they occur more frequently in cattle than other animals is probably because placental fusion and anastomosis of blood supply is very common in cattle, also explaining the high frequency of freemartins in these animals. Without a blood supply joined to that of a viable fetus (see below) an acardiac fetus can not survive.
| In humans some play is made of the fact that the viable fetus is the "pump" fetus that supplies the abnormal fetus with blood. However, this is of course the situation with any acardiac fetus because a fetus without a heart must rely on blood flow from its placenta, provided by at least one other "pump" fetus in the uterus. Therefore "pump" fetuses occur in animals as well. . |
Acardiac fetuses occur most frequently in the form of amorphous masses with hair coats and umbilical cords. In unusual cases, they may be recognizable as fetuses with legs, faces, muzzles teeth, vulva lips and tails. Rarely, two acardiac monsters may accompany a normal fetus (triplets).
As mentioned, AFs do not have hearts. Internally, they may have blood vessels, irregularly shaped bones, foci of mineralization, cartilage and fibrous tissue. In humans, AFs are usually monozygous and therefore the same sex but in cattle, the karyotypic sexes of the viable twin and the acardiac twin can be the same or different. In addition, the karyotype of the AF can be normal or abnormal. The precise genetic abnormalities leading to acardiac development are not known.
It is considered unlikely that a female co-twin to an acardiac monster can be a freemartin (because of the lack of gross male gonads in the amorphous co-twin). However, it is possible that male gonadal tissue is present if the amorphous globusus co-twin is a male. Therefore, it is wise to examine the viable female conceptus for freemartinism
Selected references
Anwar. M.T. et al. 2009. A rare case of globosus amorphus in a goat. Can Vet.: 854–856.
Blaicher. W. et al. 2000 Acardiac twin pregnancy: associated with trisomy 2: Case report. Human reproduction. 15:474-475
del Rio, N.S et al. 2006. Observed frequency of monozygotic twinning in Holstein dairy cattle. Theriogenology. 66:1292-1299
Kamimura, S. 993 A globosus amorphus from an in vitro fertilized embryo transferred to a japanese black cow. Theriogenology 40:853-858
Pearson, L.K.et al Theriogenology Question of the Month. J. Am.Vet.Med.Assn 238:1261-1263
Roberts, S.J. 1986. Veterinary obstetrics and genital diseases. Gestation period, pp 79-81. Published by the author, S.J. Roberts.
Weber J et al. 2017. Facets of Clinical Appearance and Aetiology in an Unusual Bovine Amorphus Globosus. Anat. Histol. Embryol. 46:502–506
It is considered unlikely that a female co-twin to an acardiac monster can be a freemartin (because of the lack of gross male gonads in the amorphous co-twin). However, it is possible that male gonadal tissue is present if the amorphous globusus co-twin is a male. Therefore, it is wise to examine the viable female conceptus for freemartinism
Selected references
Anwar. M.T. et al. 2009. A rare case of globosus amorphus in a goat. Can Vet.: 854–856.
Blaicher. W. et al. 2000 Acardiac twin pregnancy: associated with trisomy 2: Case report. Human reproduction. 15:474-475
del Rio, N.S et al. 2006. Observed frequency of monozygotic twinning in Holstein dairy cattle. Theriogenology. 66:1292-1299
Kamimura, S. 993 A globosus amorphus from an in vitro fertilized embryo transferred to a japanese black cow. Theriogenology 40:853-858
Pearson, L.K.et al Theriogenology Question of the Month. J. Am.Vet.Med.Assn 238:1261-1263
Roberts, S.J. 1986. Veterinary obstetrics and genital diseases. Gestation period, pp 79-81. Published by the author, S.J. Roberts.
Weber J et al. 2017. Facets of Clinical Appearance and Aetiology in an Unusual Bovine Amorphus Globosus. Anat. Histol. Embryol. 46:502–506
