Aplasia of the anterior arch of atlas associated with multiple congenital disorders: case report.

BACKGROUND AND IMPORTANCE Congenital clefts and aplasias of the atlas vertebra are rare. A nonfused posterior arch occurs in 4% of the population; in contrast, a nonfused anterior arch occurs in only 0.1%. To the best of our knowledge, this is the first description of the combination of anterior arch aplasia and a cleft of the posterior arch of the atlas associated with Klippel-Feil and Treacher-Collins syndromes and Sprengel deformity. CLINICAL PRESENTATION An 11-year-old girl presented with neck pain and symptoms of myelopathy, including upper- and lower-extremity paresthesia. Computed tomography revealed significant congenital bony anomalies of the cervical spine, with congenital fusion of C2 through C5. There was aplasia of the anterior ring of C1 (A 2.3-cm gap was present within the anterior aspect of the lateral masses). The posterior elements of C3 and C4 were fused, and signs of Sprengel deformity were present. Magnetic resonance imaging revealed effacement of the ventral cerebrospinal fluid space at the craniocervical junction and mild mass effect at the cervicomedullary junction. Flexion and extension views showed abnormal motion at the craniocervical junction. There was no evidence of atlantoaxial instability, basilar invagination, or Chiari malformation. Occipito-C4-scapular fusion was performed to prevent spinal cord injury and further neurological symptoms. Postoperatively, the patient did extremely well, and her preoperative symptoms resolved. CONCLUSION We describe a rare case of aplasia of the anterior arch of the atlas and posterior arch midline cleft in association with Treacher-Collins syndrome, Klippel-Feil syndrome, and Sprengel deformity. The patient's atlantoaxial instability was managed surgically with a unique construct that provided occipito-C4-scapular fusion.