Discussion: the case shows a sonographic diagnosis of conjoined twins at 26 weeks of pregnancy.
Definition: births of conjoined twins, whose skin and internal organs are fused together are rare. Twinning occurs in approximately 1:87 live births. Monozygotic twins account for 1/3 of twin births. Conjoined twins account for 1% of monozygotic twins. In the United States, the incidence is 1 per 33,000-165,000 births and 1 per 200,000 live births . Has also been reported in other animals—mammals, fishes, birds, reptiles, and amphibians [2, 3, 4].
Etiology: the term conjoined twinning refers to an incomplete splitting of monozygotic twins after 12 days of embryogenesis. The developing embryo starts to split into identical twins during the first few weeks after conception, but stops before the process is complete. The partially separated egg develops into a conjoined fetus. Conjoined twins are genetically identical, and are, therefore, always the same sex. They share the same amniotic cavity and placenta.
Pathophysiology: the morula becomes a blastocyst on day 6 after the ovum is fertilized. An inner cell mass develops at one end within this vesicle. The inner cell mass can form a whole fetus. Conjoined twins are produced when this inner cell mass, derived from a single zygote, incompletely splits late, after the 12th day of gestational life.
Diagnosis and sonographic findings: the prenatal diagnosis of conjoined twins is not easily made by ultrasound; there are nearly a dozen different types of conjoined twins. One of the most common type is thoracopagus twin. These twins are connected at the upper portion of the torso.
In the omphalopagus type, twins are connected from the sternum to the waist. These twins may share liver, gastrointestinal or genitourinary functions. One of the rarest types of conjoined twins is craniophagus twins, which are joined at the cranium or head. In fact, only 2% of all conjoined twins are joined in this way.
The cephalo-thoraco-omphalopagus type is extremely rare. An even more rare condition occurs when one incompletely formed (parasitic) twin is dependent on the well-formed one.
Prognosis: conjoined twins in general have been placed into 3 groups:
Group 1 - Those who do not survive delivery plus those who die shortly after birth.
Group 2 - Those who survive to undergo an elective procedure.
Group 3 - Those in whom an emergent procedure is required.
The larger the connecting bridge, the more complex its contents.
Management: Treating conjoined twins can be a daunting challenge for the surgeon. Furthermore, these cases often raise religious, moral, ethical and legal[7, 8] issues. Of all types of conjoined twins, omphalopagus twins are the most favorable candidates for elective surgery.
Mortality rates for twins who undergo separation vary, depending on their type of connection, and the organs they share
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