Chorongiopagus Parasiticus: Monster in Utero

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Chorangiopagus Parasiticus: Monsters in Utero
An interesting case presentation

Kristine G. Inocencio, MD, Medical Officer III
Department Of Obstetrics and Gynecology
Quirino Memorial Medical Center,
Quezon City, Philippines

Submitted for review May 2007

ABSTRACT

We report a case of twin gestation (diaamnionic-monochorionic) in which one of the twins had no head and poorly developed upper trunk. The co-twin appears grossly normal and both twins were stillborn. This condition is known as holoacardius or acardiac anomaly; it is a rare type of fetal twin-to-twin transfusion with an incidence of approximately 1 in 35000 births. This anomaly is thought to result from an umbilical artery-to-artery anastomosis between twin fetuses referred to as the TRAP (twin-reversed arterial perfusion) syndrome. Acardiac fetus is a rare complication of multifetal pregnancy and is incompatible with life, in most cases, a lethal condition for both the pump and parasitic twin. The mortality rate of the normal twin when an acardiac twin is present falls between 50-100%. The pathogenesis is still unknown, and recurrence has not been reported due to its rarity. It is important to be familiar with its pathologic features and classification in order to be able to perform the appropriate prenatal counselling and surveillance since such a condition can be diagnosed as early as the 12th week of gestation. Although there are no proposed guidelines for its management, the technology and the ethical implications of removing the parasitic twin in this country poses a challenge in its management. Careful post-mortem and placental examination is warranted for proper diagnosis and subsequent pregnancies are closely monitored.

INTRODUCTION
Chorangiopagus parasiticus, also referred to as: acranius–acardius, acardiac monster, acephalus, pseudocardiac, anomaly, acephalus acardia and holocardius is a rare and serious complication of twin gestations and occurs as a consequence of a TRAP (twin reversed arterial perfusion) sequence. This occurs in approximately 1% of monochorionic twin pregnancies or 1/35,000 births overall. The incidence of acardia may be 6 times as great in monochorionic, monoamnionic pregnancies as in monochorionic, diamnionic pregnancies. Most authors describe the acardiac anomaly occurring in monochorionic twin gestations; however, French et al. reported acardiac twinning in a dichorionic, diamniotic, monozygotic twin gestation. The mortality rate of the normal twin when an acardiac twin is present falls between 50-100%.

This being a rare and often fatal entity, the objectives of this report does not only include description of the case but will be elucidating problem areas in the diagnosis of such cases here in our country, as well as provide information regarding treatment options and the possible legal and moral impact it will have on the local setting. This poses the question of the appropriateness of abortions if there is risk of losing the pump twin. Grossly, such cases will show that the upper portion of the twin consists of edematous cystic tissue. This parasitic perfused twin has no placental vascular connection and its cord vessels are conjoint with those of the parasitized pump twin on the surface of the placenta or somewhere along the cord. This malformation can be identified by ultrasound as early as 12 weeks gestation. (Kakkar, et al. 2004) Figure A TRAP Sequence in a case of Monochorionic Diamnionic Twins

In TRAP sequence (Figure A), as a consequence of a reversed direction blood flow from the umbilical artery of the pump twin in into the umbilical artery of the perfused twin, via an arterioarterial anastomosis, the perfused twin’s blood supply is by definition deoxygenated and results in variable degrees of deficient development of the head, heart and upper limb structures. Two criteria seem to be necessary for the development of a TRAP sequence. The first is an arterioarterial anastomosis and the...
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