Cephalothoracopagus: A rare conjoined twins, pre and postnatal findings

Abstract

Being unique is good, but not so for conjoined twins. Cephalothoracopagus is a rare type of conjoined twins, which is a rare monozygotic twinning resulting in imperfect fusion of the head, chest and upper abdomen. These twins have separated limbs and pelvis. The incidence of conjoined twins is 1 per 50,000 to 1 per 200,000 births. The cephalothoracopagus however is very rare variant seen in 1 in 3 million births. In literature approximately 200 cases have been reported till now. The cephalothoracopagus janiceps has two types: disymmetros and asymmetros. We present a case of cephalothoracopagus janiceps disymmetros in a 22-year-old gravida at 19 weeks gestation.

Introduction

Cephalothoracopagus is an extremely rare variety of conjoined twins with imperfect ventral fusion. These twins have fused head, chest and upper abdomen (till umbilical cord level), but separated limbs and pelvis. It is seen in 1 out of every 58 conjoined twins or one out of three million births.^{1, 2, 3} The janiceps variant of cephalothoracopagus named after the two-faced Roman god has facial structures, anterior and posterior ones, from each foetus, who appears to look in the opposite directions.^{1, 2} When these faces are identical and symmetrical, cephalothoracopagus janiceps disymmetros term is used. We antenatally diagnosed a case of cephalothoracopagus janiceps disymmetros on ultrasonography (USG), further substantiated by magnetic resonance imaging (MRI) and later with gross examination post medical termination of pregnancy (Fig. 1, Fig. 2, Fig. 3, Fig. 4).

Fig. 1.

Antenatal USG. (a) Ventrally fused calvaria and cerebrums with two eyeballs (arrow mark) directed anteriorly (other pair of eyeball was directed posteriorly, not seen in image) (b) CDFI – two hearts at same level in fused thorax. (c) Fused abdomen with shared liver and two spines (arrow mark). (d) Fused abdomen at foetal kidney level with cystic dysplastic right kidney (arrow mark) of left side foetus.

Fig. 2.

Antenatal MRI (T2 HASTE) foetal axial sections. (a) Ventrally fused calvaria and cerebrums with two set of eyeballs (arrow mark) directed in opposite direction. (b) Fused thorax with two hearts at same level. (c) Fused abdomen at foetal kidney level with cystic dysplastic right kidney (arrow mark) of left side foetus. (d) Separate pelvic cavities and lower limbs of twins.

Fig. 3.

Antenatal MRI (T2 HASTE). (a) Foetal coronal section – ventral fusion from head to upper abdomen. (b) Foetal sagittal section at site of fusion.

Fig. 4.

(a and b) Gross specimen of cephalothoracopagus janiceps disymmetros.

Case report

A 22-year-old second gravida at 19 weeks of gestation was referred to department of radiodiagnosis and imaging for anomaly scan. This was the patient's first visit to the hospital. Two-dimensional (2D) ultrasound scan was performed with a Logic P5 (General Electric Medical System & Healthcare) machine equipped with a 5 Mhz convex probe. Twins were ventrally fused from frontal cranium to upper abdomen till the level of the umbilical cord. On organ assessment there was fusion of frontal lobes of cerebrums; faces were distorted with oblique fusion and two pair of eyes (looking in opposite direction) and micrognathia. They shared a common thoracic and upper abdominal cavity with two hearts, a common liver and two vertebral columns (in opposite directions). There were four pairs of well-developed limbs. A single umbilical cord was noted. The foetus on right side of mother had well developed kidneys. In left side foetus, the right foetal kidney was showing cystic dysplastic changes and left foetal kidney was not visualized. A diagnostic differential of conjoined twins with cephalothoracopagus janiceps disymmetros variety at 18 weeks 6 days gestation (calculated by foetal femur and humerus length) was made. Further confirmation of aforesaid ultrasound findings and detailed antenatal organ assessment was done with antenatal MRI scan on 1.5 T (Symphony, Siemens Medical Systems, Erlangen, Germany) MR system. Further, the spine of the left foetus appeared distorted with abnormal curvature in lumbar region; however no obvious defect or content protrusion was seen. After due informed consent of patient, medical termination of pregnancy was done at 19 weeks 3 day period of gestation by vaginal route. The gross examination after abortion confirmed the antenatal findings. Postmortem pathological analysis could not be done as the patient did not give consent. Patient/guardian consent was obtained for use of images in the study.

Discussion

Historically, as the legend goes first viable conjoined twins were the Biddenden maids born in 1100 AD.⁴ However the first well established case of conjoined twins is from the year 1811, Chang and Eng born in Siam (now known as Thailand), who became famous as “The Siamese twins”.^{2, 5}

Twins are either dizygotic or monozygotic. Dizygotic twins are almost always dichorionic-diamniotic. Monozygotic twins, depending on their time of separation are dichorionic-diamniotic, monochorionic-diamniotic or monochorionic-monoamniotic. Conjoined twins are monochorionic-monoamniotic and results when zygote divides more than 12 days after fertilization.¹ The classification of conjoined twins is very complicated and has been attempted in various classification systems. The most commonly followed system is by Spencer et al. who have further classified conjoined twins as^{1, 6}: (a) ventral union (most common) – cephalopagus (top of head to umbilicus); thoracopagus (conjoined heart); omphalopagus (including lower thorax); ischiopagus (lower abdomen and genitourinary system); parapagus (pelvis and variable trunk); (b) dorsal union – craniopagus (cranial vault); rachipagus (vertebral column); pygopagus (sacrum). Thoracopagus and omphalopagus has highest incidence among conjoined twins.^{1, 2} Cephalothoracopagus is an extremely rare variety of conjoined twins with imperfect ventral fusion. These twins have fused head, chest and upper abdomen (till umbilical cord level), but separated limbs and pelvis. It is seen in 1 out of every 58 conjoined twins or once in three million births.^{1, 2, 3} This variety further has some variants, like Janiceps and deradelphus.^{6, 7} The janiceps named after the two-faced Roman god has facial structures, anterior and posterior ones, from each foetus, who appears to look in the opposite directions. When these faces are identical and nearly symmetrical as in our case, twins are diagnosed as cephalothoracopagus janiceps disymmetros.^{1, 2} In case, there is a single hypoplastic face with part contribution from each twins, cephalothoracopagus janiceps asymmetros or monosymmetros term is used.^{2, 6} The deradelphus twins are similar to janiceps asymmetros with interchangeable use of these terms in literature. These twins have variable sharing of organs. The usual scenario is a fused cerebrum with separate posterior fossa structure as seen in our case.^{1, 2} They have two hearts, usually one is well developed and other is rudimentary,⁶ however in our case antenatal USG displayed nearly similar size of hearts. The digestive system has variable anatomy with separate or fused gastro-intestinal tract depending on case to case. They have separate spines, however any specific association with spinal anomalies is not well documented, likely due to rarity of cases itself. In our case, one of the twins was having distorted and abnormal curvature of lumbar spine with no obvious defect. On post termination gross analysis, no skin defect was seen in lower back. These twins have separate excretory system as seen in our case, though one of the twins had mal-developed kidneys.

The earliest possible diagnosis of conjoined twins can be made around 7–9 weeks period of gestation on trans-vaginal and trans-abdominal sonography respectively.² However the precise evaluation of degree of fusion and visceral sharing can be done on USG between 18 and 20 weeks of gestation. MRI helps in confirmation of diagnosis as well as in detailed evaluation of visceral assessment antenatally. This is especially important in those variant of conjoined twins where chances of viability are bright and future surgical separation is contemplated. A postnatal MRI of conjoined twins further helps in surgical planning. However as in our case, cephalothoracopagus variants of conjoined twinning are non-viable and not amenable to surgical separation due to their complex cerebral fusion and visceral sharing.^{2, 6, 8} These cases need to be diagnosed antenatally at earliest to provide an option to parents for medical termination of pregnancy. The same was done in our case with pregnancy termination at 19 weeks 3 days. The postnatal findings confirmed antenatal diagnosis of cephalothoracopagus janiceps disymmetros. In conclusion, cephalothoracopagus janiceps disymmetros is an extremely rare variant of conjoined twins with ventral fusion from head to upper abdomen and variable visceral sharing. A timely antenatal diagnosis helps in counselling the parents about poor neonatal outcome and planning medical termination of pregnancy.

Disclosure of competing interest

The authors have none to declare.