According to Official Guinness Records,
Vilija and Vatalija Tamulevicius (Lithuania) (b.30 July 1987), were born sharing a skull and the vasculiture of the brain - a caniopagus connection. Dr. Alexander Konovalov (Russia), separated the girls on 6 July 1989, but their bodies rejected the artificial skulls and so the girls were taken to Texas, Dallas, USA, where Dr. Kenneth E. Salyer (USA), rebuilt their skulls . Previous to this, every head separation had resulted in either brain damage or death to at least one of the twins - the sisters returned to Lithuania with no brain damage
For a complete list of 1990 records, please visit 1990 Guinness Records in United States.