Atlantoaxial dislocation with congenital "sandwich fusion" in the craniovertebral junction: a retrospective case series of 70 patients.

Sandwich fusion AAD, a unique subgroup of AAD, has distinctive clinical features and associated malformations such as cervical-medullar compression, syringomyelia, and VA anomalies. Surgical treatment of AAD was associated with myelopathy improvement and minimal complication occurrence.