Siamesische Zwillinge

Illustrates
various types of chorionicity and amniosity (how the baby"s sac looks) in monozygotic (one egg/identical) twins as a result of when the blastocyst or embryo splits.
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Prenatal
diagnosis and postnatal findings of cephalothoracopagus, janiceps, monosymmetros twins. 3D ultrasound image of (A)- fetal face, showing low set ear, enlarged head and retrognathia. (B) 2 lower limbs arising from 2 pelvices with common upper abdomen.
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Prenatal
diagnosis and postnatal findings of cephalothoracopagus, janiceps, monosymmetros twins. Antenatal ultrasound and post mortem CT axial views of fetal head show 2 cerebral hemispheres forming an inverted V shape and partially fused thalami in an enlarged head.
www.eurorad.org • CC by-nc-sa-4.0
Prenatal
diagnosis and postnatal findings of cephalothoracopagus, janiceps, monosymmetros twins. Antenatal ultrasound and post mortem CT axial views of fetal head show 4 cerebellar hemispheres.
www.eurorad.org • CC by-nc-sa-4.0
Prenatal
diagnosis and postnatal findings of cephalothoracopagus, janiceps, monosymmetros twins. A- Axial view of head shows 2 well-developed eyes. 2 pituitary glands are noted in sella tursica. B- Axial view, bone window shows 4 internal ear structures.
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Prenatal
diagnosis and postnatal findings of cephalothoracopagus, janiceps, monosymmetros twins. Ultrasound and postmortem CT images of axial view of thorax show 2 spines facing each other and 2 hearts. The superior heart appears relatively normal while the inferior heart is hypoplastic.
www.eurorad.org • CC by-nc-sa-4.0
Prenatal
diagnosis and postnatal findings of cephalothoracopagus, janiceps, monosymmetros twins. Ultrasound and postmortem CT axial images of upper abdomen showing 2 livers and 2 spines.
www.eurorad.org • CC by-nc-sa-4.0
Prenatal
diagnosis and postnatal findings of cephalothoracopagus, janiceps, monosymmetros twins. Coronal and sagittal volume-rendered CT images with skeletal rendering showing fused skull vault, 2 spines with partial fusion of posterior elements of C3 to C5 vertebrae in both spines and 8 limbs.
www.eurorad.org • CC by-nc-sa-4.0
Prenatal
diagnosis and postnatal findings of cephalothoracopagus, janiceps, monosymmetros twins. Postmortem CT coronal image through right atrium. Formalin is acting as contrast agent. Hepatic veins converge into IVC and drain into right atrium. Another vessel is draining into right atrium from left side inferiorly.
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Fig. 87.
X-ray of joined twins, cephalothoracopagus. (Courtesy Herman Klapproth, M.D., and Eastman Kodak Co.)
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Radiopaedia • CC-by-nc-sa 3.0 • de

Conjoined twin pregnancy is a rare occurrence resulting from the failure of a zygote to separate completely after 13 days . This results in the twins being physically joined.

Epidemiology

The prevalence of conjoined twins ranges from 1:50,000 to 1:200,000. They are more common in parts of Southeast Asia and Africa with prevalence rates as high as 1:14,000 to 1:25,000. There is a recognized female predisposition (F: M of approximately 3:1).

Pathology

Embryology

Conjoined twins are monozygotic, monoamniotic, and monochorionic (MCMA) (see multifetal pregnancy) and result due to a failure of normal complete separation of the embryonic plate from an incomplete delayed division of the inner cell mass. This is thought to occur around 13-17 days of gestation.

Classification

Conjoined twins are classified according to the most prominent site of interconnection

Ventral union
Dorsal union
Lateral union

If more than one area is connected the terms are combined, e.g. thoraco-omphalopagus (thoracic and abdominal fusion).

Other descriptive terms include:

  • diprosopus: two faces with one head and body
  • dicephalus: two heads with one body
  • syncephalus: facial fusion with or without thoracic fusion
Associations

There is a higher incidence of congenital malformations in conjoined twins (10-20%) which are unrelated to the point of fusion such include

Radiographic assessment

Antenatal ultrasound

Thus identification of a dividing membrane or two placentas excludes the diagnosis. Definitive sonographic features will depend on the type of fusion.

General features include:

  • lack of a separating inter-twin membrane
  • non-separable skin contours with an inability to separate the fetal bodies
  • detection of other anomalies in a twin gestation
  • solitary umbilical cord with more than 3 vessels present
  • both fetal heads persistently at the same level
  • backward flexion of the cervical spine (due to the fact that most conjoined twins are fused ventrally and face each other
  • bibreech or less commonly, bicephalic presentation
  • constant relative fetal positions

Treatment and prognosis

The prognosis for conjoined twins, in general, is quite poor. Approximately 40-60% of conjoined twins are stillborn and almost 35% of live births do not survive beyond 24 hours. Of those who do survive, surgical separation is sometimes possible (but with higher failure rates if performed within the first 3 weeks ). Surgical separation, in general, is in most cases very challenging with high mortality, depending on the complexity of shared structures. Of those with thoracopagus, ~75% have extensively joined hearts which in turn preclude a successful separation.

Siehe auch:
und weiter:
Assoziationen und Differentialdiagnosen zu Siamesische Zwillinge:
Mehrlingsschwangerschaft
 
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Zwillingsschwangerschaft
 
Wikipedia • CC BY 3.0