Congenital fusion of C2 - C3, Radiology Case

Fusion of adjacent vertebral segments is not an unusual isolated abnormality and should not be confused with the far less common Klippel Feil syndrome. 

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Frontiers Os odontoideum associated with a retro-odontoid cyst treated with posterior C1–C3 fixation: A case report and literature review

Klippel Feil syndrome – a case report

Atlanto-occipital assimilation, Radiology Reference Article

Anomalies Radiology Key

Radiographic Assessment of Congenital C2–3 Synostosis

Asian Spine Journal

Diagnostics, Free Full-Text

Radiology In Ped Emerg Med, Vol 5, Case 5

Cureus, A Consultation for Pediatric Neck Mass Resulting in a Rare Diagnosis of Klippel-Feil Syndrome: A Case Report

Cranio-cervical decompression associated with non-instrumented occipito-C2 fusion in children with mucopolysaccharidoses: Report of twenty-one cases - North American Spine Society Journal (NASSJ)

Anomalous vertebral arteries in Klippel-Feil syndrome with occipitalized atlas: CT angiography - ScienceDirect