WASHINGTON, June 7: US surgeons were forced to halt a delicate and high-risk procedure to separate twin girls joined at the head because of unexpected brain swelling, doctors said on Thursday.

Three-year-old Anastasia and Tatiana Dogaru, whose parents are from Romania, were described as “medically stable” at Rainbow Babies and Children's Hospital in Cleveland, Ohio, after a first round of surgery on Wednesday to begin separating their skulls.

But doctors were hesitant to go further until they determined the cause of the swelling in the dominant twin, Anastasia, which was discovered after neurosurgeons took out a section of skull to expose the brain tissue. “After removing the bone, it became apparent that the brain tissue was swollen, despite the fact that measures had been taken to prevent such swelling,” chief medical officer Nathan Levitan told a news conference.

“They felt that it would not be safe to cut into the brain tissue or the surrounding blood vessels in any way, without first understanding the cause of the swelling and the low blood pressure,” Levitan said.

“As a result, they decided not to continue with surgery at that time,” he said, adding that an MRI and angiogram would be studied to determine the next step.

The twins have never looked one another in the face, because the top of Tatiana's head is attached to the back of her sister Anastasia's head. Their brains are connected “in a complex fashion,” and they also suffer from heart, organ and limb defects, a hospital statement said.

Their condition, known as total angular craniopagus, is extremely rare and considered fatal without treatment, comparable to being diagnosed with a malignant, inoperable brain tumour, it said.

Pre-operation procedures began last month when doctors inserted wire coils into brains' blood vessels to create independent circulation for each child. The girls share the same circulatory system, so that any medication administered to one affects the other. Doctors feared that as the girls grew, the risk of one getting sick could endanger both of their lives.

“There is a sense of urgency, because if one twin were to become severely ill and die, the other twin would most likely die within minutes or hours of the first. The longer the twins remained conjoined, the more likely it is that one will become ill,” the hospital said.

Doctors noted that the girls were fortunate to be alive since most cranial conjoined twins die at birth and only 10 per cent live until the age of 10, but admitted it was “a very high-risk surgery in which one or neither of the twins may survive.” The twins' parents, Claudia and Alin Dogaru, both 31, brought the girls to the United States from Rome, Italy, where they were born, after seeing a news story about Egyptian conjoined twins who underwent successful separation surgery in Dallas, Texas.—AFP