OBGY Radiology

Imaging Finding

Conjoined Twins (Janiceps type)

Fig 1 & 2: MR ssFSE T2W images with fused calvaria and colpocephaly
Fig 3 & 4 : Two pairs of eyeballs (i.e. 4 orbits) in opposite directions
Fig 5 : Fusion of the neck, thorax and abdomen is also seen. Spine is separate. Two urinary bladders and an umblical cord are seen. The hypointensities in the liquor consist of parts of extremities and cord as well
as artifacts due to are due to fluid motion.
Fig 6: MR 3D reconstruction model showing Janiceps type of cranio-thoraco-abdominopagus deformity with two eyes and separate limbs


Discussion

Magnetic resonance imaging of a moving fetus was always considered difficult because of the longer scanning time. Ultrafast magnetic resonance imaging with faster gradients and new software enables rapid imaging of the fetus. This enables imaging quality superior to two-dimensional ultrasonography and should be considered an adjunct to ultrasonography for characterization of some fetal abnormalities (1). MRI has emerged as a useful imaging technique because of high resolution, ability to characterize tissues and inherent capability to generate information in three planes (2).

Conjoined (Siamese) twins are rare with an incidence of 1 in 30,000 to 1 in 1,00,000 births (3). The frequency is independent of maternal age or parity and it occurs sporadically. Conjoined twins result from monozygotic twinning when the embryo does not split until after the second week of gestation (4).

They are classified according to the location of the tissue that links the twins as craniopagus (joined at cranium), thoracopagus (joined at the thorax), omphalopagus (joined at the anterior abdominal wall), pyopagus (joined at buttocks and lower spine and lying back to back), and ischiopagus (joined at sacrum and coccyx and lying side to side). Early antenatal diagnosis and assessment of the rare entity of conjoined twins helps in determination of postnatal viability, which depends on the organs shared and whether surgical correction is possible. Many anatomical abnormalities are common among conjoined twins. Congenital heart disease ( most commonly a ventricular septal defect or Tetralogy of Fallot ) is present in 75% of thoracopagus twins. The liver is shared in 81% of omphalopagus twins. In craniopagus twins, the prognosis depends on the degree of connection between the brains (5).

Janiceps type of cephalo-thoraco-abdominopagus twins is even more rare. Its incidence is 1 in 3 million conjoined twins (6). It derives its name from Janus, the god of doors and gateways, his statue with two faces, facing east and west for the beginning and ending of the day (6,7). Survival of conjoined twins depends on the presence or absence of associated anomalies. The surgical challenges include separation of the important shared organs and closure of defects in bones and soft tissues (2).

Complex congenital anomalies are optimally evaluated with sonography and magnetic resonance imaging. With the advent of ultrafast imaging sequences, magnetic resonance imaging of the fetus is now easier. It allows demonstration of anatomical details in a three dimensional perspective. Magnetic resonance imaging is considered to be superior to other modalities in illustrating neurosurgical abnormalities in craniopagus twins (8). Magnetic resonance imaging simplifies the work-up of conjoined twins, without the risks of ionizing radiation or injection of radio-opaque contrast. To assist in planning the separation, a three-dimensional computer model of the conjoined twins can be constructed on the basis of the prenatal magnetic resonance imaging studies, as in our case. This helps the surgeons and the parents to have a better visualization of the anomaly. Because of the ability of magnetic resonance imaging to enhance the visualization of abnormal anatomy, the surgeon can deal with greater confidence and can plan potentially safer operations for all types of conjoined twins (6).

Magnetic resonance imaging can be conveniently performed in cases of conjoined twins. It complements and enhances the diagnosis made on ultrasonography. High resolution whole body images are useful in counseling the parents on the degree of abnormalities and the multiplanar images are well understood even by the non-radiologists. The accurate identification of the extent of fusion helps rational decision making and planning for the surgery, if possible.

BIBLIOGRAPHY:
1. Casele HL, Meyer JR. Ultrafast MRI of cephalopagus conjoined twins. Obstet Gynecol 2000 Jun; 95[6(20]:1015-7.
2. Norwitz ER, Hoyte LPJ, Jenkins KJ, Van der Velde ME et al. Separation of conjoined twins with the twin reversed-arterial-perfusion sequence after prenatal planning with three-dimensional modeling. Normal Engl J Med 2000; 343(6):399-402.
3. Hanson JW. Incidence of Conjoined twins.Lancet 1975; 2:1257.
4. Rumack CM, Wilson SR, Charboneau JW. In: Diagnostic Ultrasound. 2nd ed. New York: Mosby; 1998:2;1043-1068.
5. Twining Parietal, McHugo J, Pilling DW. In: Textbook of Fetal abnormalities. 1st ed. China: Churchill Livingstone; 2000:401-404.
6. Hernandez-Valencia M, Baruch PRA, Ferrer PLA, Alvarez MM. Janiceps Cephalo-thoraco-abdominopagus pregnancy. Ginecol Obstet Mex 1998 Dec;66:499-502.
7. Abossolo T, Dancoisne Parietal, Tuaillon J, Orvain E, Sommer JC, Riviere JP. Early prenatal diagnosis of asymmetric cephalothoracopagus twins. J Gynecol Obstet Biol Reprod (Paris) 1994;23(1);79-84.
8. Richardson RJ, Applebaum H, Taber Parietal, Woolley MM, Chwals WJ, Warden MJ, Dietrich R. Use of Magnetic Resonance Imaging in planning the separation of omphalopagus conjoined twins. J of Pediatr Surg 1989 July;24(7):683-685.

Dr Sona Pungavkar, MRI Centre, Nanavati Hospital, Mumbai.