Dubai Hospital, OB-Gyn Dept., Dubai , UAE

Synonyms: incomplete monozygotic twins, diplosomia, Siamese twins

Definition: Dicephalus dipus dibrachius is an extremely rare form of conjoined twinning in which the infant has two arms, two legs, one trunk, but two heads.

Case report:  A 22- year-old woman, primigravida, at 21 weeks of gestation presented with complaints of mild edema of the feet and a high blood pressure (150/95). The patient perceived good fetal movements. Her antenatal follow-up done in a private clinic was unremarkable. The patient was married for a year to her second cousin (secondary consanguinity). The pregnancy was conceived spontaneously. The patient denied any contact with potential hazards. Her past history was unremarkable. Her family history was not relevant for any congenital anomaly. The patient had a twin sibling.

Ultrasonography was performed on admission. A fetus with features of dicephalus having good fetal movements was seen. The amniotic fluid volume was increased. Single placenta was situated posteriorly. Parameters were corresponding to 19 weeks. One of the heads had a dilatation of lateral ventricles, the other one was anencephalic, with well visualized orbits and nasal bones. There was an evidence of duplication of spine, with two well defined vertebral columns, fused in the lumbar region. The rest of thoracic and abdominal visceral organs seemed to be single, with no gross anomalies (one heart with normal 4-chambers view, one stomach, two kidneys and one urinary bladder). The fetus had one pair of lower limbs and one pair of upper limbs.  There was unusual hyperextension of cervical spine belonging to “normal” head. Sagittal view of spine showed certain irregularity and diversion of spine in thoracic region. A single umbilical artery was also noted.

After discussion, the parents decide to interrupt the pregnancy. After birth, a dicephalic fetus with male external genital organs and morphological features was diagnosed. Plain X-rays were performed, demonstrating the skeletal anomalies. The parents refused anatomical-pathological study.

Image showing ventriculomegaly, hyperextension of cervical spine. Note the irregularity in thoracic part of spine.

View of the anencephaly. Note normal appearance of face on the left and the polyhydramnios

Left image: View of the normal and anencephalic heads. Right image: Transverse plan showing two distinct vertebral columns, fused caudally. Single heart.

2-vessels cord (color Doppler).

Polyhydramnios and the single umbilical artery

 Postnatal view. Note the correlation of morphological features with the sonographic images

X-ray reveals two heads (one of them being anencephalic), one thorax with duplication of spine fusing in lower lumbar region, one pair of upper limbs and a shared abdomen, pelvis and a single pair of lower and  limbs.

Etymology: from Greek [di=double + -cephalus=head ,   di- + pus= leg ,   di- + brachius=arm]  meaning “ the one with two heads, two legs and two arms”.

History: Throughout history, conjoined twins have appeared in myths and legends. The Greek and Roman god Janus had two faces, one young, one old. Centaurs, a combination of horse and man, may have been inspired by parapagus twins who often have four legs. A common heraldic symbol, the "Double-Headed Eagle", is common throughout Central Europe.

There are many instances of dicephalic monsters on record. The French Renaissance surgeon Ambroise Pare mentions and gives an illustration of a female apparently single in conformation, with the exception of having two heads and two necks. The Ephemerides, Haller, Schenck, and Archenholz cite examples, and there is an old account of a double-headed child, each of whose heads were baptized, one called Martha and the other Mary; they only lived a couple of days. There is another similar record of a Milanese girl who had two heads, but was in all other respects single, with the exception that after death she was found to have had two stomachs. Besse mentions a Bavarian woman of twenty-six with two heads, one of which was comely and the other extremely ugly .

Figure 1. Types of conjoined twins depicted by French Renaissance surgeon Ambroise Pare.  He identified the major types of conjoined twins, but he provided superstitious accounts for their origin. (From On Monsters and Marvels (orig, 1573), University of Chicago Press, Chicago, 1982.

Figure 2. The Tocci Brothers.

Figure 3. Skeleton of parapagus twins, showing fusion of the lower half. Courtesy of the Mütter Museum, Philadelphia.

A more common occurrence of this type is with a fusion of the two heads. Moreau speaks of a monster in Spain which was shown from town to town. Its heads were fused; it had two mouths and two noses; in each face an eye well conformed and placed above the nose; there was a third eye in the middle of the forehead common to both heads. Each face was well formed and had its own chin. Buffon mentions a cat, the exact analogue of Moreau"s case. Sutton speaks of a photograph sent to Sir James Paget in 1856 by William Budd of Bristol. This portrays a living child with a supernumerary head, which had mouth, nose, eyes, and a brain of its own. The brain of the supernumerary head was quite visible from without, and was covered by a membrane beginning to slough. On the right side of the head was a rudimentary external ear. Home speaks of a child born in Bengal with a most peculiar fusion of the head. The ordinary head was nearly perfect and of usual volume, but fused with its vertex and reversed was a supernumerary head. Each head had its own separate vessels and brain, and each an individual sensibility, but if one had milk first the other had an abundance of saliva in its mouth.

Prevalence: Conjoined twins occur in approximately 1:40,000 births, but only 1:100,000 to 200,000 live births. 60% of conjoined twins are either stillborn or lost in utero, and 35% of twins that survive die within the first 24 hours; i.e. only 26 sets of 100 conceptions of conjoined twins will survive birth and the first 24 hours. Conjoined twins are most likely to be girls (71%), probably because male twins are more likely to be miscarried (as are all normal male babies). They are most likely to occur in India or Africa than in China or the US. Although the rates in Vietnam have been much higher in recent years, possibly due to Agent Orange exposure. The birth rate of conjoined twins in Africa is approximately 1:14,000 births. 1:400 identical twin pregnancies will be conjoined twins.

Etiology:  Conjoined twins may be caused by any number of factors, being influenced by genetic and environmental conditions (like orange agent). It is presently thought that these factors are responsible for the failure of twins to separate after the 13th day after fertilization. Assisted conception techniques such as IVF and ICSI may be a factor (10). Conjoined twins can be artificially generated in amphibians by constricting the embryo so that two embryos form, one on each side of the constriction.

Embryology: Four days after fertilization the trophoblast (chorion) differentiates. If the split occurs before this time the monozygotic twins will implant as separate blastocysts each with their own chorion and amnion. Eight days after fertilization the amnion differentiates. If the split occurs between the 4th and 8th days, then the twins will share the same chorion but have separate amnions. If a split occurs after the 8th day and before the 13th day, then twins will share the same chorion and amnion. This is a very rare condition and accounts for 1-2% of monozygotic twins. The embryonic disk starts to differentiate on the 13th day. If the split occurs after day 13, then the twins will share body parts in addition to sharing their chorion and amnion. (3)

However, some studies provide convincing evidence that they all result from the secondary union of two originally separate monovular embryonic discs. This fusion  theory seems to be confirmed by the adjustments to union and the pattern and incidence of specific anomalies at the proposed sites of conjunction.
 No theoretical  fission  of the vertebrate embryo at any stage of development, in any plane, in any direction can explain the selection of the observed sites of fusion,  the details of the union, or the limitation to the specific areas in which the twins are found to be jointly separate monovular embryonic discs.(1)

Classifications: Conjoined twins are usually classified by the point at which they are joined (the Greek word pagos, meaning "that which is fixed."). There have been as many as three dozen separate types identified in the last century. The following basic classifications can be combined to more closely define individual cases.

Cephalopagus - Anterior union of the upper half of the body with two faces on opposite sides of a conjoined head. The heart is sometimes involved.  No picture available Syncephalus - Joined by the face, containing a single head and two bodies. Syncephalus twins will have one head and a single face with four ears, two on the back of the head.  

Cephalothoracopagus - Fused from the head to chest. There is only one brain and head (sometimes a rudimentary 2nd face), and they usually share a heart and have fused gastrointestinal tracts. They are non-viable. Also called Epholothoracopagus or Craniothoracopagus. Janiceps or Janus twins usually share one body with one head and two faces.  

Thoracopagus - United face-to-face from the upper thorax down to the umbilicus, with heart involvement, 90% have a shared heart. Four arms, four legs, two pelvises.  

Omphalopagus - Joined face-to-face primarily in the area of the umbilicus, and sometimes involving the lower thorax, but always preserving two distinct hearts. Two pelvis, four arms and four legs.  

Thoraco-Omphalopagus: Combination of thoracopagus and omphalopagus, these twins will be attached from the upper chest to the umbilicus, and will usually share a heart. About 90% of the conjoined thoraco-omphalopagus twins have a common pericardium and 75% have conjoined hearts. Also may have shared livers and gastrointestinal tracts. Four arms and four legs are present.  

Xiphopagus: Joined at the xiphoid process (the smallest of the three divisions of the sternum, below the gladiolus and manubrium). They are joined roughly from the navel to the lower breastbone. These twins rarely share vital organs aside from the liver.  

Ischiopagus - United from the umbilicus to a large conjoined pelvis with two sacrums and two symphyses pubis. They are joined end-to-end with the spine in a straight line. Four arms, a variable number of legs, and in general, a single external genitalia and a single anus. Ischiopagus Dipus - Only two legs are present. Ischiopagus Tripus - Three legs are present. Many have only one set of external genitalia. The third leg can be fused (two legs fused into one), or vestigal (non-functioning). Ischiopagus Tetrapus/Quadripus- Four legs are present   Omphalo-Ischiopagus - A combination of omphalopagus and ischiopagus, these twins present joined as ischiopagus twins are, but face-to-face with a joined abdomen. Four arms, and a variable number of legs are present.        Lateral union: twins joined side-by-side with shared umbilicus, abdomen, and pelvis    

Parapagus - Twins that share a conjoined pelvis, one symphysis pubis and one or two sacrums, united side by side. When the union is limited to the abdomen and pelvis (does not involve the thorax) it is called dithoracic parapagus. If there is one trunk with two heads it is called dicephalic parapagus (dicephalus).  

 If there is a single trunk and a single head with two faces they are diprosopic parapagus.  

 Types of parapagus twins include: Dibrachius: two arms are present (About 10% of all dicephalus/dithoracic twins) Tribrachius: three arms are present. Tetrabrachius: four arms are present.      Dorsal union: twins joined at the dorsal aspect (at the back). There is no involvement of thorax and abdomen    

Craniopagus - United on any portion of the skull, except the face or foramen magnum (base of the skull). They share bones of the cranium, meninges, and occasionally brain surface. Two trunks, four arms and four legs. Accounts for about 2% of all conjoined twins. The twins can be joined end to end (vertical), at the back of the head (occiptal), front of the head (frontal), side of the head (parietal/temporal).  

Pygopagus (also seen as Pyopagus or Illeopagus) - They dorsally share the sacrococcygeal, perineal regions and occasionally the spinal cord. There is one anus, two rectums, four arms and four legs. Accounts for about 19% of all conjoined twins.  

Rare forms of conjoined twins, having different patterns:

• • Parasitic twins: Asymmetrical conjoined twins, one twin being small, less formed, and dependent upon the other.
  • Fetus in fetu: Situation in which an imperfect fetus is contained completely within the body of its sibling.

An attempt to standardise and classify conjoined twins according to the external forms of conjunction has been proposed by Leacham (Table 1). (2)

Classification of dicephalus:

• dicephalus dipus dibrachius: a fetus with two heads but only two feet and two arms.
• dicephalus dipus tetrabrachius: conjoined twins with only two legs, but with varying degrees of fusion of the upper trunk, each component having a head and pair of arms.
• dicephalus dipus tribrachius: a fetus with two heads, two feet, but with a median third arm or arm rudiment.
• dicephalus dipygus,   anakatadidymus.
• dicephalus parasiticus,   desmiognathus.
• dicephalus tripus tribrachius: a fetus with a common trunk, but with two heads, three arms, and three legs, the third limbs being either rudimentary or complete.

Sonographic findings:

Implications for targeted examinations: Antenatal diagnosis by ultrasound is possible in modern day obstetrics. Conjoined twins should be suspected in all monochorionic, monoamniotic twin pregnancies, and careful sonographic assessment should be performed to identify the presence of shared fetal organs. (6) Ultrasonographic identification of any of the following classical signs may suggest the diagnosis: lack of separating membrane, inability to separate fetal bodies, 3 or more vessels in cord, or alternatively 2-vessels cord (5), both fetal heads in the same plane, unusual backward flexion of the cervical spine, no change in the relative position after maternal movement and manual manipulations and inability to separate fetal bodies after careful observation. (7)

Differential diagnosis: The condition should be differentiated with following: multiple gestation, teratoma, cystic gyroma, neoplasm, parasitic twin.

Associated anomalies: Among the most frequent anomalies associated with conjoined twinning are duplication of visceral organs, omphalocele, facial clefts, meningomyelocele and imperforate anus (10). Cardiac defects are the frequently reported findings as well.

Prognosis: There are reliable reports of unseparated dicephali reaching maturity; 1 pair (the Tocci brothers) reached at least 34 years of age. In the absence of concomitant cardiac, pulmonary, and intestinal malformations, dicephalus conjoined twins may well attain adulthood. This appears to be unrelated to whether they have 4 (dicephalus tetrabrachius) or 3 (dicephalus tribrachius) arms at birth.(4) Prognosis, obstetric management, and treatment planning are determined by degree of fusion and extent of joining of fetal organs(9).

Recurrence risk: appears to be negligible.

Management: Prior to 24 weeks of gestation vaginal delivery is appropriate. Cesarean section is recommended in most third-trimester deliveries because of the high incidence of dystocia and resultant fetal damage and risk of maternal morbidity. (9)

References :

1 - Conjoined Twins, by Rowena Spencer, published by Johns Hopkins Press, Baltimore, MD.

2- Gerlis LM, Seo JW, Ho SY, Chi JG. Morphology of the cardiovascular system in conjoined twins: spatial and sequential segmental arrangements in 36 cases. Teratology. 1993; 47:91- 108.

3- Finberg HJ. Ultrasound Evaluation In Multiple Gestation. In Callen"s Ultrasonography in Obstetrics and Gynecology:Harcourt Publishers 3rd edition,1994;Chapter 8:121-124.

4- Bondeson J. Kennedy Institute of Rheumatology, Hammersmith, London, England.  Copyright 2001 by W.B. Saunders Company.

5-Koontz, WL, Herbert, WN, Seeds, JW, Cephalo, RC: Ultrasonography in the diagnosis of conjoined twins; A report of two  cases. J Reprod Med 28:627, 1983.

6- Levi CS, Lyons EA, Martel MJ, Dashefsky SM, Holt SC. Sonography in the diagnosis and management of Multifetal Pregnancy. In Rumack"s Diagnostic Ultrasound: St. Louis, Mosby- Year Book Inc,1997;Chapter 35: 1062-1065.

7- Kalchbrenner M, Weiner S, Templeton J, Losure TA. Prenatal Ultrasound Diagnosis of Thoracophagus Conjoined Twins. J Clin Ultrasound 1987; 15: 59-63.

8- Y. Goldberg, I. Ben-Shlomo, E. Weiner and E. Shalev , First trimester diagnosis of conjoined twins in a triplet pregnancy after IVF and ICSI: Case report  Human Reproduction, Vol. 15, No. 6, 1413-1415, June 2000

9- Tandon R, Sterns LP, Edwards JE. Thoracopagus Twins. Arch Pathol 1974; 98: 248-251.

10-Romero R, Pilu G, Jeanty P et al: Prenatal  Diagnosis of Congenital Anomalies. Norwalk, CT, Appleton &  Lange, 1988, pp 405-409.