Conjoined twins

BYDr. CHINMAY . P . MEHTA

RESIDENT AT KIMS HUBLI &NMR INSTITUTE .

ABSTRACTOne of the most interesting congenital malformations is a conjoined twin. Conjoined twins are a rare occurrence. More commonly known as Siamese twins,after First Siamese twins "exhibited" in America in 1829 ,Chang and Eng born in SIAM(Thailand)•Current technology is providing a basis for earlier diagnosis and a better prognosis.Magnetic resonance imaging and CT scan provide excellent anatomic detail, demonstrating organ position, shared viscera, and vascular anatomy.•We present a case of Thoraco-omphalopagus Conjoined Twins.

Case report22 year old women, primigravida,with 7 months of amenorrhea , 2nd degree consanguineous marriage & no family history of twins. She had a previous antenatal Ultrasound report at 16weeks which read as twin pregnancy. She presented to our hospital at 31 weeks. Sonography was performed which showed following:•Two fetuses with all 4 pair of limbs and two cranial cavities(dicephalus, tetrabrachius)•The twins were joined at the thorax and upper abdomen. •Single umbilical cord(5vessel), shared liver,omphalocoele, and only one fetal heart which appeared normal.•One fetus (acardia)had hydrocephalus with poor visualization of lungs and kyphoscoliotic spine.•To confirm our findings and get more details we did a fetal MRI.MRI confirmed our usg findings. •On the basis of these findings, the diagnosis of terata anacatadidyma, thoraco-omphalopagus, conjoined twins was made, and the parents were informed about the malformation and the twins' poor chance for survival. The parents decided to terminate the pregnancy.Caesarean section was done and twins were delivered as breech. •Twins had single male external genitalia, weighing 3 kg together. Placenta was single.• An USG and CT w was done to further assess them; findings of antenatal scans were confirmed.

cardia liver

Spine A

SPINE B

CARDIA-POST NATAL POST NATAL

hydrocephalus

HYDROCEPHALUS

OMPHALOCOELE

SHARED LIVER

CARDIA

OMPHALOCOELE

INTRODUCTION

• Conjoined twins are rare, but the exact prevalence is unknown. The estimated prevalence in the literature varies widely from 1: 50,000 to 1: 200,000.

• There is a female predominance on the order of 3:1

• The conjoined twinning process occurs when the division of the embryonic disc occurs more than 14 days after fertilization.

EMBRYOLOGY• The twinning process occurs in the very early stages of

embryogenesis. Division after the 14th day of fertilization results in an incomplete division, because once it becomes an embryo, it is incapable of fusion. The later the division, the more severe the effect.

• Duplicata incompleta is the most severe form of incomplete division, because division is so late and incomplete, only a few organ systems are duplicated. This makes surgical division impossible.

• Many variations of conjoined twins are possible. It is customary to name these large lateral fusions, which incorporate multiple regions, on the basis of the anatomic part that remains double and separate; for example, dicephalus, two heads with fusion of the thorax and abdomen

CLASSIFICATION.• Inferior conjunction: lower body is single, or twin joined by some lower portion of

the body • Duplicata completa = terata catadidyma Ischiopagus: joined by the lower portion of the coccyx & sacrum Pygopagus: joined by the lateral and posterior aspect of the coccyx and sacrum

• Middle conjunction: midbody fusion with separation of the upper and lower portion of the body

• Duplicata completa = terata anacatadidyma Thoracopagus: joined by the chest wall Omphalopagus: joined between the umbilicus and the xyphoid process Rachipagus: joined by the spine, above the sacrum • Superior conjunction: upper body is single, or twin joined by some lower portion

of the body • Duplicata completa = terata anadidyma Syncephalus: joined by the face Craniopagus: joined by the skull.( Site of fusion + suffix "pagus“)

USG DIAGNOSIS CRITERIA

• Demonstration of a continuous non seperated external skin contour.

• Bifid appearance of the fetal pole in first trimester• Conjoined body parts.• Body parts of the twins are imaged on the same level and in the

same sonar plane.• No change in the relative position of the twins to one another and

on successive scans.• Monochorionic twinning-Single placental mass/ No inter-twin

membrane• More than 3 vessels in a single umbilical cord.• Complex multiple fetal anomalies.

THORACOPAGUS• Thoracopagus twins are united face to face from the upper

thorax to the umbilicus with a common sternum, diaphragm, and upper abdominal wall. Ninety percent of such twins have a common pericardial sac, and there is always a degree of cardiac fusion.

• The liver is invariably fused, and 25% of thoracopagus twins share a biliary system. Initial liver assessment can be performed with US. However, in twins joined anteriorly, there is limited probe access; when viewed from the side, the conjoined liver is oriented in an oblique plane to the axis of the probe .

• A better appreciation of liver anatomy is gained from multiplanar techniques, ideally MR imaging.

• It is important to evaluate bile excretion by using dynamic biliary scintigraphy with Tc-99m HIDA

OMPHALOPAGUS• Omphalopagus twins are joined ventrally in the

umbilical region, often including the lower thorax.• Liver fusion occurs in approximately 80% of cases.

As there is no mixing of blood in the cardiac chambers, the liver can be well assessed by using CT with intravenous injection of contrast material into one twin.

• Gadolinium-enhanced MR imaging can also be used in this context. As described in the section on thoracopagus twins, biliary scintigraphy can be helpful in determining biliary drainage

ROLE OF COLOR DOPPLER & 4D

• Color doppler is very useful in evaluation of liver blood supply-Common portal vein precludes separation & also to evaluate number and orientation of hepatic veins.Also very useful in craniopagus.

• 4D-Easier for parents to understand & helps in counselling.Better surface views

• But 2D and Doppler better to determine degree of organ sharing

ROLE OF MRI

• Pre-surgical planning - Fetuses stable on placental support - No sedation required - Defines degree of organ sharing - T2WI excellent for brain/renal/chest detail - Tl WI for additional bowel and liver information• Clarify anomalies - Either fetus may have lethal anomaly in addition to being conjoined. - Information may influence management Termination of pregnancy. Requirement for emergent separation. Mode of delivery

PROGNOSIS

• The prognosis for conjoined twins is generally unfavorable, with approximately 40% of cases stillborn. The worst prognoses concern craniopagus twins and those with a sole cardiac mass. Structural anomalies are frequently found such as polyhydramnios (50%), cardiac malformations, common omphaloceles, and neural tube defects. Upon discovery of nonviable conjoined twins, interruption of pregnancy should therefore be recommended

MANAGEMENT

• In the case of potentially viable conjoined twins, after 24 weeks GA the choice between vaginal delivery or prophylactic caesarian section should be made based on maternal safety and neonatal criteria. Caesarian section avoids dystocia, uterine rupture, and fetal death in utero.

• Approximately six to ten cases of conjoined twins per annum worldwide are treated surgically. The surgery is most successful when commonality of fetal organs is limited; surgical intervention often takes place around one year of age

CONCLUSION

• Diagnosis of conjoined twins is possible as early as 8 weeks GA, but accurate evaluation of common structures is not possible. The 12-week scan allows clinicians to assess viability, and, in the case of nonviability, to propose early medical interruption of pregnancy, preventing hysterotomy in the case of a delayed termination. Early discovery of viable conjoined twins permits assessment of the best route of delivery and a planning for serial sonography and fast MRI to plan separation surgery

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