Classification and its clinical significance of basilar invagination

English Keywords:Basilar invagination  Classification  Stable type  Unstable type

English Abstract:

  【Abstract】 Objective：To investigate the classification of basilar invagination so as to provide a criterion for surgery determination.Method：70 cases suffering basilar invagination determined by radiography，CT and MRI from March 2007 to March 2010 in our hospital were divided into two groups（stable group and unstable group） based on present of atlas-occipital or atlas-axis dislocation.The deformities such as occipital-atlas fusion，Chiari malformation，slippage of the axis facets，syringomyelia were recorded.Several parameters including clivus slope，distance from odontoid to Chamberlain line and distance form odontoid to foramen magnum line were measured，and the spine medulla compression and the surgical approach of each group were recorded respectively.Result：20 cases were termed as stable and 50 as unstable.Among the stable group，there were 18 Chiari deformity（90%） and 15 syringomyelia（75%）；while among the unstable group，there were 2 Chiari deformity （4%），46 occipital-atalas fusion（92%），37 slippage of upper facets（74%），and 43 syringomyelia（86%）.And the clivus slope angle was 168°±5° and 133°±11° for stable and unstable group respectively（P<0.05）；the distance from odontoid to the Chamberlain line was -4.8±4.2mm and -5.6±3.7mm for stable and unstable group respectively（P>0.05）；and the distance form odontoid to the foramen magnum line was 0.5±0.3mm and -6.9±2.9mm for stable and unstable group respectively（P<0.05）.In the stable group，2 cases complicated with ventral medulla compression，11 with dorsal and 7 cases with both underwent the posterior cranial fossa decompression；while all 50 unstable cases（44 with ventral and 6 with both ventral and dorsal medulla compressions） experienced transoral anterior release and instrumentation.Conclusion：The basilar invagination can be divided into two types based on present of atlas-occipital or atlas-axis dislocation，which is used to differentiate the anatomic and clinical characters for both groups and to determine the correspondent surgical approach.