The Baby With A Second Head

MIAMI (Reuters) - An international team of doctors hopes to operate in the Dominican Republic next month to remove an undeveloped second head from a baby girl born with one of the world's rarest birth defects, caused when a conjoined twin fails to develop in the womb.

The baby, Rebeca Martinez, was born in mid-December at a hospital in Santo Domingo with the head of an undeveloped twin attached to the top of her skull, facing upward.

The infant is otherwise healthy but her brain cannot develop normally unless the undeveloped head is removed, said Dr. Santiago Hazim, medical director at the CURE International Center for Orthopedic Specialties, where the surgery is tentatively set for February 6 or 7.

Her condition, cranio pagus parasiticus, is so rare that there have only been eight documented cases in the world, and no known cases where surgery has been attempted to correct it, Hazim said in a telephone interview.

Conjoined twins form when an embryo begins to split into identical twins and then stops, leaving them fused. Twins conjoined at the head account for about one of every 2.5 million births and about 2 percent of all conjoined births.

Rarer "parasitic" twins occur when one conjoined twin stops developing in the womb, leaving a smaller, incompletely formed twin that is dependent on the other. They can form as an extra limb, torso or head, or as a complete second body, lacking vital organs.

In Rebeca's case, there is a gap in her skull where the heads are joined, and the blood vessels are intertwined, Hazim said. The vestigial head is enlarged and fringed with dark hair like Rebeca's but has a poorly developed brain and only rudimentary facial features, he said.

Rebeca was born weighing about 7 pounds and now weighs over 10 pounds, but the undeveloped head is drawing away nutrients and exerting pressure on Rebeca's brain.

"She was able to go home after a couple of days in the hospital," Hazim said. "She's getting some weight on ... She cries, she wakes up in the morning like a normal child."