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Types of Conjoined Twins

There are many different types of conjoined twins. The types are determined by the orientation of the connection. The name of each type is broken down into "the type of connection" + "-pagus" (meaning "that which is fixed" in Greek). Not every case of each type of conjoined twins are the same either. There are variations within each type.

Craniopagus

Classified as united on any portion of the skull, except for the face and foramen magnum. The trunks are not united, and there are four arms and four legs. The brain and meninges are usually shared. Craniopagus is a rare form of twinning, with around a 2% occurrence.




Ahmed and Mohamed Ibrahim. Two-year old conjoined twin boys from Egypt that were attached at the head, but had separate brains. On October 13, 2003, they were surgically separated, after a 34-hour operation, from one another at a hospital in Dallas, Texas.


Cephalopagus

Classified by fusion from the top of the head down to the umbilicus. There are two faces on opposite sides of the conjoined head. The lower abdomen and pelvis are not united, and there are four arms and four legs. Cephalopagus is another rare type of conjoined twinning. There has not been a case where these types of twins survived after birth.


Dicephalus

Classified as a child born with two heads, two spinal columns, two arms and two legs, but share a single body with multiple internal organs. Like all the other twinning types that involve the head, dicephalus is a rare form.

Abby and Brittany Hensel. More information on their case in the "Life Conjoined" link on the menu bar.


Thoracopagus

Classified as united face to face from the upper thorax down to the umbilicus. The union always involves the heart. The pelvises are not conjoined, and there are four arms and four legs. The heart, liver, and intestines may be potentially shared. Thoracopagus is the most common form of conjoined twinning, with about a 37% occurence.



Jade Hope and Erin Faith Buckles. These conjoined twins were attached from the mid-chest to their belly button. They shared a pericardium, diaphragm, and liver. They shared the same heartbeat, and were successfully separated on June 19, 2004. Erin became permanently paralyzed in both her legs from a spinal cord injury during the operation, but both twins are living normal lives and are relatively healthy.


Omphalopagus

Classified as fetuses that are joined face to face, primarily in the area of the umbilicus. The union often includes the inferior lower thorax, but never the heart or intercardiac vessel. The pelvises are not united, and there are four arms and four legs. The liver and intestine are normally shared. Omphalopagus is also a pretty common form of conjoined twinning, with an occurrence of around 30%.










Chang and Eng Bunker. More information on their case in the "Life Conjoined" link on the menu bar.


Ischiopagus

Classified as united from the umbilicus down to a large conjoined pelvis with two sacrums and two symphises pubis. There are four arms and four legs, and the external genitalia and anus are always shared. The liver and intestine may also be shared. Ischiopagus occurs about 6%.


Pygopagus

Classified by fetuses that are joined back to back with fused buttocks. This may result in a shared spine and rectum. The occurrence of pygopagus twinning occurs about 17%.



Heteropagus

Heteropagus is also known as parasitic twinning. It is the condition where one of the conjoined twins never develops completely, but are still attached to the living twin. A specific condition of heteropagus twinning is called fetus in fetu, where the smaller twin grows incompletely inside the abdomen of the larger twin. Surgical removal of the undeveloped parasitic twin is usually preferred.



Lakshmi Tatma. Known as the "girl with 8 limbs." She was born with four arms and four legs, with the extra limbs coming from her partially developed parasitic twin that was attached at her pelvis. The four extra limbs were surgically removed successfully. The surgeons kept some of the structures of the parasitic twin in order to reconstruct Lakshmi's pelvis. Many people in India saw this little girl as a goddess when she still had her 8 limbs. However, her parents were more concerned with their daughter's well-being and possible normal life in the future.