Imaging Assessment Of Craniocervical Junction Instability

Objective:To generalize typical CT findings of craniocervical junction instability, and to evaluate the reliability and the validity of our 0～2 grade classification. Analyse its clinical syndrome and related factors.Materials and methods:Analyse prespectively 242 consecutive cervical spine CT materials which were performed with axial volume scan routinely and got sagital,axial,coronal images with MPR technique. Choose patients according to the predeterminated diagnosis criterion of craniocervical junction instability,then perform volume rendering reformation. Select randomly 50 asymptomatic volunteers as control group. All patients and asymptomatic volunteers were performed with protondensity-weighted MRI in three orthogonal planes. Changes in the alar ligaments,transverse ligament and tectorial ligament (grades 0-2) based on the ratio between the high signal area and the total cross-sectional area were rated twice at a 2-week interval independently by two radiologists.Inter-and intraobserver statistics were calculated by weighted kappa.Results:60 patients of atlantooccipital or atlantoaxial joint instability were chosen from 242 CT scan cases,including of 21 occipital atlantal and 39 atlantal axial joint instability.34 males and 26 females, mean age 38 years, range 28-66 years.All 21 cases of atlantooccipital joint instability were divided into 3 types according to the translation direction of condyle:13 condyles appeared posterior translation on atlas,5 patients showed unilateral condyle rotated on the atlas, and another 3 condyle appeared posterior translation associated with axial rotation. It is the typical finding that the anterior bone margine of atlantooccipital joint stepped posteriorly at the space level in sagital image(n=21).Other important findings include that lateral bone margine of joint translated to the opposite in coronal image(n=7), widen space between arcus anterior atlantis and condyle in axial image(n=11). distortion of C1 intervertebral foramen (n=15). Flatten of the posterior part of the atlantal superior facet (n=15).All 39 cases of atlantoaxial instability were divided into 4 types according to the translation direction and the rotatory condition of the atlas:7 atlas dislocated anteriorly,6 atlas subluxated laterally,5 atlas rotated on the axis,and another 21 atlas demonstrated axial rotating associated with lateral translating. Important CT findings included:ADI ranged in 3.5-5.7mm, mean 4.3mm(n=7). odontoid process translated laterally 1.5～2.2mm, mean 1.8mm(n=32). Bilateral atlantoaxial facet shifted in the same direction(n=6).atlas rotated to left or right in VR image(n=26).2 in 3 patiens associated with osteoarthritis of atlantoaxial joint demonstrated huge osteophyte protruding into C2 intervetebral foramen and resulting in its'deformation.37 cases have nomal shape of C2 intervetebral foramen.7 in 60 craniocervical unstable patients were associated with upper cervical development malformation. Atlantooccipital membrane were absent in 4 patients,Alar ligament undeveloped in 4 cases (bilateral in 3, unilateral in 1 patient). It was reliable of Our 0～2 grade system to assess morphology alteration of alar,transversal ligament and tectorial membrane, Pair-wise interobserver and intraobserver agreement(weighted kappa) were good(Kappa>0.6),while the agreement was fair for atlantooccipital membrane (Kappa<0.4).The incidence of higher grade(1～2 grade) was higher in research group than nomal control (P<0.05). There was significant correlation between alar high signal in PDWI (1～2 grade) and odontoid process lateral translation, likewise between transversal ligament high signal and ADI widen, while not between tectorial membrane high signal and the type of craniocervical unstable.Conclusion:CT spiral scan with multiplanar reformation combined with MR proten sequence have a great role in detecting the morphology alteration of the bone and main ligament of the craniocervical junction. It is reliable of our 0～2 grade system to assess the severity of alar, transversal ligament or tectorial membrane lesion which are responsible for the occipito-atlanto-axial stable.