Dicephalic parapagus twins

Giacomo and Giovanni Battista Tocci

Dicephalic parapagus is a rare form of partial twinning where there are two heads side by side on one torso.^[1] Infants conjoined this way are sometimes called "two-headed babies" in popular media.^[2] The condition is also called parapagus dicephalus.^[1]

If carried to term, most dicephalic twins are stillborn, or die soon after birth.^[3] A small number are known to have survived to adulthood.^[3]

The extent to which limbs and organs are duplicated varies from case to case. One head may be only partially developed (anencephalic),^[4] or both may be complete. In some cases, two complete hearts are present as well, which improves their chances of survival.^[5] The total number of arms may be two, three or four.^[3]

Their prospects are best if no attempt is made to separate them, except in cases where one twin is clearly dying.^[6]

Terminology

Skeletal structure of dicephalic twins. From: Hirst & Piersol, 1893.

Dicephalus means two-headed.^[1] Parapagus means joined side by side.^[7][1]

Dicephalic twins are called:

• dibrachius if they have two arms altogether (one for each twin),^[3]
• tribrachius, if they have three arms altogether,^[8]
• tetrabrachius, if they have four arms altogether,^[7]
• dipus, if they have two legs altogether (one for each twin).^[7]

Incidence

Conjoined twins appear in one in 50,000 to one in 100,000 births.^[9] Dicephalic twins represent about 11 percent of all conjoined twins.^[9]

Medical and social response

As late as the 1960s, some medical publications argued that newborn dicephalic twins should not be actively treated or resuscitated.^[10] An attempt at surgical separation was reported in a paper published in 1982, but did not result in long-term survival of either twin.^[11] In more recent cases in Turkey and Minnesota, doctors advised that separation surgery would not be appropriate.^[12][13]

Dicephalic twins who survived past infancy

Giacomo and Giovanni Battista Tocci (1877–1940), were Italian male dicephalus parapagus twins who survived to adulthood.^[9][14] Each had his own pair of arms.^[14] They had two legs altogether, one of which was controlled by each twin.^[15] They were exhibited in freak shows as children and teenagers. The Toccis learned to speak several languages,^[16] but never learned to walk.^[14]

Abby and Brittany Hensel, born in Minnesota in 1990, are another instance of dicephalus parapagus twins who grew up.^[17] They were born with two functional arms, plus a vestigial third arm, which was surgically removed.^[13] Each twin has her own complete head, heart and spine, and controls one arm and one leg.^[13] They learned to walk around the same age as average children, went on to attend school, learn to drive, play sports,^[13] and completed courses at college. They now teach in an elementary school.^[18]

Twin girls conjoined like the Tocci brothers, with four arms and two legs altogether, were born in Turkey in 2000.^[12] As with the Toccis and the Hensels, it was found that each twin controlled one leg.^[19] Because of the size of their upper body, the Turkish twins needed a special program of exercises before they could learn to walk.^[19] After that, they learned to run and climb stairs without further specialist help, and at age 11 they were going to school with other children.^[20]

See also

• Craniopagus parasiticus is another form of partial twinning which results in two heads kept alive by a single torso. In these cases a second, vestigial torso is present, and the heads are joined directly to one another.^[21]
• Diprosopus is a condition in which there are duplicated facial features on one head.
• Polycephaly is a general term about organisms with more than one head.

References