Radiological Evaluation of 510 Cases of Basilar Invagination with Evidence of Atlantoaxial Instability (Group A Basilar Invagination).

Abstract

To evaluate the musculoskeletal and soft tissue neural alterations in cases with group A basilar invagination. Between January 2007 and August 2016, 510 patients with group A basilar invagination were surgically treated. The radiologic images of these patients were reviewed retrospectively. The patients were divided into 4 groups: group A1, comprising 60 patients with syringomyelia; group A2, comprising 354 patients with "external syrinx," marked by excessive cerebrospinal fluid (CSF) in the extramedullary space; group A3, comprising 51 patients with both syringomyelia and external syrinx; and group A4, comprising 45 patients with no abnormality of CSF cavitation in the spinal canal. A number of musculoskeletal and neural parameters, including the extent of basilar invagination, degree of angulation of the odontoid process, and facet malalignment, were evaluated in each of the 4 groups. The degree of basilar invagination was 6-27.4 mm (average, 15.85 mm) in group A1, 4.3-24.5 mm (average, 12.56 mm) in group A2, 5.6-17.6 mm (average 10.8 mm) in group A3, and 5.2-17.3 mm (average, 11.74 mm) in group A4. The angle of inclination of the odontoid process was 61.1-90.7 degrees (average, 71.4 degrees) in group A1, 30.5-79.8 degrees (average, 60.05 degrees) in group A2, 68.5-78.3 degrees (average, 73.4 degrees) in group A3, and 62.2-87.4 degrees (average, 71.2 degrees) in group A4. The nature of bone malformations directly influences the presence or absence of external syrinx and syringomyelia.