by Dr Noreen Norfaraheen Lee Abdullah MD (UKM), MMed Radiology (UKM), AM(Mal)

Answer to Case Of the Month 
Conjoint Twins

Discussion of Findings
There is a large skull, which is asymmetrical in shape. The skull demonstrates enlargement and broadening of the left occipital and parietal bones. Single facial structures such as a pair of orbits, one nasal bone, a pair of maxilla and single jawbone observed. The whole spine, ribcage, pelvis, genital organs, upper and lower limbs are present in complete pairs. Soft tissue fusion of the upper abdomen and thorax noted.

The features are in keeping with conjoint twins – cephalothoracopagus type

Progress/Outcome
The baby was ventilated for 2 hours before it passed on following drops in oxygen saturation and heart rate on several occasions.

Conjoint twinning is rare and occurs once in 50,000 to 100,000 births. It occurs due to incomplete division of the embryonic cell mass in monozygotic twins, the incident usually occurring at 13-16 days of gestational age.

There are several types:

1. Inferior conjunction:
   a) Diprosopus: two faces, one head and body
   b) Dicephalus: two heads, one body
   c) Ischiopagus: joined by inferior sacrum and coccyx
   d) Pyopagus: joined by the posterolateral sacrum and coccyx

2. Superior conjunction:
   a) Dipygus: single head, thorax, abdomen, two pelves and four legs
   b) Syncephalus: facial and thoracic fusion
   c) Craniopagus: joined between the homologous portions of the cranial vault

3. Middle conjunction:
   a) Thoracopagus: joined between the thoracic walls, conjoined hearts
   b) Omphalopagus: joined between the umbilicus and xiphoid
   c) Xiphopagus: joined at xiphoid

4. Others:
   a) Cephalothoracopagus: fused heads and thoraxes but two separate spines, limbs, and pelvises
   b) Thoracoomphalopagus: joined between the thorax and abdomen
   c) Incomplete duplication: duplication of only one part of the body

About a decade ago, conjoint twins were not detected till the 3rd trimester when labor became obstructed. Diagnosis is best during pregnancy at the first trimester utilizing ultrasound. Features favouring conjoint twins are single placenta with inseparable fetal bodies. Both heads are persistently at the same level and there is no change in the fetal position. The fetuses face each other. Bibreech/bicephalic presentation is usually observed with the bibreech position more common. Single umbilical cord with more than three vessels is a supportive finding and in most cases there is polyhydramnios.

This case highlights the importance of prenatal ultrasound for the detection of such rarity, which when known earlier would allow for better evaluation, understanding and better management.

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Last Updated:
Sunday, 15 January 2012