Surgeons in New York say they have successfully separated two-year-old Filipino twins who were conjoined at the head, CNN reports Thursday.

More than twelve hours into the operation doctors teased apart the adjacent portions of Carl and Clarence Aguirre's brains, a Montefiore hospital statement said.

The brothers -- who were born in the southern Philippines and arrived in America in mid-September -- survived the procedure, but doctors warned that several more hours of delicate and difficult surgery is still needed.

The 16-member medical team was able to separate the shared system of veins that drained blood from the bothers' brains.

After the procedure the twins' head-to-head operating tables were pulled apart slightly, the statement said.

Because of the network of delicate veins located in the back of the brain, the work to isolate and separate them was meticulous and time-consuming.

It is the first time conjoined twins have been separated in a multi-stage procedure.

Instead of opting for the typical marathon two-day operation, doctors in this case chose four shorter procedures over ten months.

Doctors chose this approach because it meant a shorter time under anesthesia and a lower risk of massive bleeding and injury to the brain.

The time between procedures also allowed the twins to recover physically from the blood-vessel separation and to undergo rehabilitation and physical therapy, the doctors added.

In the earlier surgeries, doctors placed balloons underneath the twins' scalps in a procedure that allows tissue to expand.

The balloons were gradually inflated with sterile saline, stretching and expanding the scalp so that enough skin would be available to cover their separated heads.

Neurosurgeons also tied off shared veins in an effort to reroute the boys' shared vascular system.

Surgeons must now reconstruct a thin sac of tissue lining the brains that have been shared up to this point of their lives.

They then have to cover their heads with skin.

Reconstruction of the boys' skulls will take place at a later date.

Source: Agencies