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Occipitalization of the atlas in children. Morphologic classification, associations, and clinical relevance
Purushottam A Gholve1, Harish S Hosalkar, Eric T Ricchetti
1Division of Orthopaedic Surgery, Children's Hospital of Philadelphia, 2nd floor, Wood Building, 34th Street and Civic Center Boulevard, Philadelphia, PA 19104, USA.
Insights
Occipitalization, a congenital fusion of the atlas to the occiput, is linked to spinal canal narrowing and instability in children. Imaging can classify patterns and predict outcomes.
Area of Science:
- Pediatric Neurosurgery
- Congenital Spinal Abnormalities
- Craniovertebral Junction Disorders
Background:
- Occipitalization is a congenital fusion of the atlas to the occiput.
- Previous studies have not detailed morphologic patterns or implications in children.
- This study presents the largest series of pediatric occipitalization cases evaluated with advanced imaging.
Purpose of the Study:
- To describe morphologic patterns of pediatric occipitalization.
- To investigate associated craniovertebral junction anomalies and clinical characteristics.
- To establish a classification system for occipitalization based on imaging findings.
Main Methods:
- Retrospective review of pediatric occipitalization cases from a spine database.
- Development and application of a new morphologic classification system (Zones 1, 2, 3) based on CT/MRI.
- Evaluation for cervical instability, spinal canal encroachment, and other craniovertebral anomalies.
Main Results:
- Thirty pediatric patients with occipitalization were identified (24 boys, 6 girls; mean age 6.5 years).
- Morphologic patterns included Zone 1 (6 patients), Zone 2 (5 patients), Zone 3 (4 patients), and combined zones (15 patients).
- Atlantoaxial instability occurred in 57% of patients, C2-C3 fusion in 8, and spinal canal encroachment in 37% (highest in Zone 2).
Conclusions:
- Occipitalization is frequently associated with spinal canal narrowing and craniovertebral junction abnormalities.
- Congenital C2-C3 fusion significantly increases the risk of atlantoaxial instability.
- A 3-zone classification system using 2D CT/MRI reconstructions aids diagnosis and prognostic assessment.
Background:
Occipitalization is defined as a congenital fusion of the atlas to the base of the occiput. We are not aware of any previous studies addressing the morphologic patterns of occipitalization or the implications of occipitalization in children. We present data on what we believe is the largest reported series of children with occipitalization studied with computed tomography and/or magnetic resonance imaging, and we provide a description of their clinical characteristics.
Methods:
We retrospectively reviewed all cases of occipitalization in children included in our spine database. Patient charts and imaging studies were reviewed. A new morphologic classification of occipitalization was developed from the two-dimensional sagittal and coronal reformatted computed tomographic reconstructions and/or magnetic resonance images. The classification includes four patterns according to the anatomic site of occipitalization (Zones 1, 2, and 3 and a combination of those zones), and it was applied to this group of patients. Imaging studies were also reviewed for evidence of cervical instability and for other anomalies of the craniovertebral junction.
Results:
Thirty patients with occipitalization were identified. There were twenty-four boys and six girls with a mean age of 6.5 years. The morphologic categorization was Zone 1 (a fused anterior arch) in six patients, Zone 2 (fused lateral masses) in five, Zone 3 (a fused posterior arch) in four, and a combination of fused zones in fifteen. Seventeen patients (57%) had atlantoaxial instability, and eight of them had an associated C2-C3 fusion. Eleven patients (37%) had spinal canal encroachment, and five of them had clinical findings of myelopathy. The highest prevalence of spinal canal encroachment (63%) was noted in patients with occipitalization in Zone 2.
Conclusions:
Occipitalization is associated with abnormalities that lead to narrowing of the space available for the spinal cord or brainstem. The risk of atlantoaxial instability developing is particularly high when there is an associated congenital C2-C3 fusion. Two-dimensional sagittal and coronal reformatted computed tomographic reconstructions and/or magnetic resonance images can help to establish the diagnosis and permit categorization of occipitalization in three zones, each of which may have a different prognostic implication.
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