Twin sisters Anastasia and Tatiana Dogaru were born joined at the head and doctors say they cannot perform surgery to separate the 4-year-old girls.

The twins were born in Rome and have never looked each other in the eye because the top of Tatiana's head is attached to the back of Anastasia's. Twins conjoined at the head, known as craniopagus twins, occur about once in every 2.5 million births. A doctor brought the twins to the United States for a surgical evaluation and concluded it will be impossible to operate.

Anastasia relies on Tatiana for her kidney functions and one of the girls' brain is growing into the other, making surgery no longer an option. Doctors concluded it would be highly unlikely that the girl's brains could recover from the separation.

Doctors now hope the twins, who live in Chicago with their parents, can live as normal a life as possible, but their long-term prognosis is unknown.