Classification of Conjoined or Simese Twins
Conjoined or Simese Twins is the rare entity of twins. They were born from the same egg and developed as monozygotic monochorionic monoamniotic type with incomplete separation of the embryo at the late stage. Classification according to the embryonic duplication was clearly indicated the pathophysiology, pattern of the conjoined organs was recommended in order to plan about the management and surgical separation. The classification was useful for stating the prognosis and also for comparison the result of the treatment in various pediatric surgical centers.
Embryogenesis
Classification
The most favorite classification for monozygotic twin suggested by Wilder was the followings :
1. Free Monozygotic Twins
Totally separation of twins
1.1 Symmetrical twins : same sex and very much alike
1.2 Asymmetrical twins (Acardius) : one is perfectly formed but another is not well formed
1.2.1 Hemiacardius : some part of the less formed baby is missing but the core structures remain
1.2.2 Holoacardius : more and important part of the less formed baby is missing i.e., No head - Holoacardius acephalus, No trunk - Holoacardius acormus, Unidentified structures - Holoacardius amorphus
2. Equal Conjoined Twins or Diplopagus
2.1 Equal conjoined entire twins
2.1.1- cranial fusion : craniopagus
join at vertex or frontal or occipital region
2.1.2- anterior fusion
join on ventral surface of the body - sternopagus, xiphopagus, sternoxiphopagus, thoracopagus, xipho-omphalopagus, omphalopagus
2.1.3- posterior fusion
join on dorsal surface of the body - pygopagus
2.1.4- pelvic fusion
ischiopagus fusion of two set of complete pelvis
(must be differentiate from the Dicephalus tri (or tetra)brachius tri (or tetra) pus which had only one set of pelvis or fusion of incomplete pelvis)
2.2 Conjoined Imperfect Twins
This type of conjoined twins caused by incomplete duplication of primitive streak lead to imperfect formation of each baby and conjoining. This type of twins may be called " Monsters"
2.2.1- Duplication of the cranial part only - Monocephalus diprosopus
2.2.2- Duplication of the upper part of body with only one set of lowe part of body - 2 legs) - Dicephalus dipus group
-Dicephalus dipus dibrachius
-Monocephalus tripus dibrachius
-Monocephalus tetrapus dibrachius
2.2.4- Duplication of both lower and upper part of the body by most parts joined each other
-Cephalothoracopagus syncephalus
-Dicephalus tripus tribrachius
-Dicephalus tripus tetrabrachius
-Dicephalus tetrapus tribrachius
-Dicephalus tetrapus tetrabrachius
3. Unequal Conjoined Twins - Heteropagus or Parasitic Twins
Perfect baby called Autosite
Imperfect part called Parasite
References
1. Wilder HH. Duplicate twins and monsters. Am J Anat 1964 ; 3 : 387
2. Votteter TP. Conjoined twins. In : Welch KJ, Randolph JG, Ravitch MM, O’Neill JA Jr., Rowe MI, eds. Pediatric Surgery, 4th edition. Year Book Medical Publishers. 1986 : 771-9
