Congenital midline cleft of the posterior arch of atlas: a rare cause of symptomatic cervical canal stenosis.

Developmental symptomatic C1 canal stenosis is very rare. We describe the computed tomography (CT) and magnetic resonance imaging (MRI) appearances in a 8-year-old child who presented with progressive upper and lower limb neurological symptoms and in whom imaging revealed the medial posterior hemiarches of a bifid C1 to be inturned and compressing the cervical cord. This particular configuration of the posterior arch of atlas is frequently associated with other craniocervical bony anomalies and presents with neurological symptoms early in life. Early CT or MRI examination of patients with symptomatic posterior arch of C1 defects is necessary, in order to detect such an appearance, since surgical treatment may prevent neurological deterioration.