Craniopagus Parasiticus and the Unformed Conjoined Twin

Craniopagus parasiticus is an extremely rare type of parasitic twin that results when twins are joined at the head but one does not fully develop. The skulls are fused together but only one twin develops a body while the other does not. The twin who develops is referred to as the autosite twin and the one that doesn't develop is called the parasitic twin.

Causes of Craniopagus Parasiticus

Conjoined twins occur when the process that separates most identical (monozygotic) twins doesn't result in a complete separation. This usually occurs eight to 12 days after conception. But if the split happens a few days later it may stop before it is complete. There is also a possibility of two embryos fusing together. Parasitic twins differ from conjoined twins in that one twin fails to develop fully, perhaps due to a degeneration of the umbilical cord. This condition is so rare that it isn't known what might be a risk factor.

When conjoined twins are attached at the skull, they may be attached at the back, top, or side. They are not attached at the face. They may share a portion of the skull and may share some brain tissue.

Diagnosis and Prognosis

Parasitic twins will most often be diagnosed with ultrasound findings. In many cases, they will die in the womb or shortly after birth. The baby usually must be delivered by cesarean section. Each case is unique and the family and doctors have to assess whether separation may be successful. There are legal and ethical considerations that must be addressed in each case.

As neurosurgical techniques have improved, there have been some separations that have been successful, at least in the short term. Three cases using a two-stage technique were reported as successful in 2012.

The Case of Manar Maged

Worldwide attention focused on an Egyptian baby named Manar Maged after an episode of The Oprah Show aired sharing her story with the world. The child was born on March 30, 2004. A second skull with a face was attached to Manar's skull. This skull, named Islaam, could blink and smile and had a separate brain. But Islaam relied on Manar's organs to sustain life, which endangered her due to heart trouble. The weight would also prevent Manar from crawling or sitting upright. This led to a decision to attempt to detach the parasitic twin.

A 13-hour surgery was performed on February 19, 2005, at Benha Children's Hospital north of Cairo, Egypt to detach the parasitic twin. Manar was released from intensive care in March 2005. She showed no signs of paralysis and could move all of her limbs. However, she developed hydrocephaly, which is an accumulation of fluid in her brain. On March 25, 2006, she passed away from a brain infection shortly before her second birthday. She was the first case that had a successful operation, although it did not lead to a long-term successful outcome.