Acardius amorphous: Description, Causes and Risk Factors:An acardius amorphous is a rare complication of multifetal pregnancy, with a reported incidence of 1% of monochorionic twin pregnancies, i.e. 1 of 35,000 pregnancies. It occurs as a result of twin-reversed arterial perfusion (TRAP) sequence when both twins derive their blood supply from a single placenta. If one twin's cardiac function develops more slowly in early pregnancy, imbalance of blood pressure between the twins results in retrograde flow of poorly oxygenated blood to the heart of the abnormal twin. This interferes with the development of the heart so that it rarely progresses beyond a rudimentary stage of development. In most cases, the lower body and extremities develop to a certain degree but poor perfusion (and under oxygenation) to the upper body leads to underdevelopment of this area. The acardiac twin is a lethal condition while the normal twin is at risk of cardiac failure.There has been a good deal of speculation about the possible pathogenesis of acardiac monsters. The circulation has been well described. Briefly, the umbilical arteries of both twins anastomose on the placental surface or shortly before they reach the placenta. The arterial pressure resulting from the heart action of the normal twin causes a reversal of the direction of blood flow within the umbilical arteries of the weaker twin. Hence perfusion of the monster occurs with blood depleted in oxygen and nutrients.There are two main theories of etiology:The blood pumped from the umbilical artery of the first twin into the second, being deficient in oxygen and nutriments causes the recipient twin to become so poorly nourished and anoxic that it develops imperfectly. The monster's heart, being overcome by the reversed flow of blood, then atrophies. This seems to be the most popular theory.
Primary failure of the parts to develop adequately, the chances of anastomoses of the two arterial systems merely allowing the potentially blighted ovum to survive during the antenatal period.
There are several features which suggest that the popular concept of deficient nutrition being responsible for the malformation.Symptoms:Signs & Symptoms may include:This variety is the least well developed, bearing no resemblance at all to a human fetus. It usually consists of an ovoid mass with no attempt at head or limb formation.
Moderately well developed limbs are usually present.
In some cases there consists of a head without a body.
Diagnosis:The diagnosis is almost invariably made postnatally. The only way in which the diagnosis couldbe made antenatally is by X-ray, and only then byconstant alertness for the condition. On the rareoccasions that acardiac monsters have been X-rayedin utero they have been mistaken for anencephalics.The normal twin is usually born first, the deliverybeing uncomplicated. Rare cases of dystocia resulting in abdominal delivery have been reported. There seems to be no increasedincidence of associated abnormalities in the accompanying twin, nor is there any report of the malformation having occurred more than once in thesame patient.Because the diagnosis is usually made from antenatal ultrasound scans by the obstetricians and MRI maybe useful as an adjunct incases to assess the presence of retrogradeblood flow in the acardiac fetus and umbilical artery.Prenatal diagnosis of acardiac twin is usually made with ahigh degree of sensitivity using US scan.Fetal echocardiography is recommended to assist with early detection of heart failure in the normal twin. Chromosome studies are recommended for both fetuses in all pregnancies complicated by acardius amorphous.Treatment:There is no consensus on which therapy is best for pregnancies complicated by acardius amorphous sequence. The goal of prenatal therapy is to help the normal twin. The normal twin is not always saved by prenatal treatment.Specialists have used laser and electrical cauterization, electrodes, serial amniocentesis, medications, and other treatments successfully. Physicians often recommend prenatal interruption of the blood vessel connections (thus sacrificing the acardiac twin) before heart failure develops in the pump twin.Cutting off blood circulation to the acardiac twin can be accomplished by cauterizing or burning the blood vessel connections. In a 1998 study of seven pregnancies treated with laser therapy the rate of death in the normal twin was 13.6%, a vast improvement over the expected 50% death rate. Current studies examining the success and failure rates of these treatments will be helpful in determining which therapy is the best option.NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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