Craniopagus twins

Craniopagus twins are conjoined twins who are fused at the skull. The union may occur on any portion of the cranium, but does not primarily involve either the face or the foramen magnum; the two brains are usually separate, but they may share some brain tissue. Conjoined twins are genetically identical and always share the same sex. The thorax and abdomen are separate and each twin has their own umbilicus and umbilical cord.

The condition is extremely rare, with an incidence of approximately 1 in 2.5 million live births. An estimated 50 craniopagus twins are born around the world every year as of 2021, with only 15 twins surviving beyond the first 30 days of life. Relatively few craniopagus twins survive the perinatal period; approximately 40% of conjoined twins are stillborn and an additional 33% die within the immediate perinatal period, usually from organ abnormalities and failure.

However, 25% of craniopagus twins survive and may be considered for a surgical separation; several such attempts occur annually worldwide. Advances in neuroimaging, neuroanesthesia, and neurosurgery have demonstrated that a successful outcome is possible. Among all conjoined twins, craniopagus twins account for a mere 2% to 6%.