In the most severe form, rachischisis, the opening is extensive.

Patients with rachischisis have motor and sensory deficits, chronic infections, and disturbances in bladder function.

P. Erdinçler, et al. suggests from their findings that the cause of the anomaly is actually a defect in the occipital bone and rachischisis of the posterior vertebral arches leading to herniation of neural tissue through the opening in the bone during gestation.