| Objective To establish reference criteria on normal angles at the cranial base and the cranio-cervical junction (CCJ) on MRI and to create a new method for the diagnosis of basilar invagination by MRI. Methods The associated angles were calculated based on the distances measured between ten points on MRI Ti WI and TiWI of the central sagittal slices at the cranial bases and the CCJs of 106 cases of normal Chinese, two patients with BI and three patients with Chiari malformation. Results The normal ranges of the angle of the anterior margin of the subarachnoid space (SAS) at the CCJ (AACC), the angle of the cranial base margin of the SAS at the superior posterior margin of the d o r s u m sellae (ACBM) and AACC minus ACBM (AA-AC) are 1 39.2 ~163.9 , 1 05.4 ~129.5 and 15.4 ~52.7 in male, and are 1 35.5 ~160.7 , 1 1 0 . 1 ~13 1 .2 and 7.7 ~47.1 in female. The angle of the posterior margin of the SAS at the CCJ (APCC) and AACC minus APCC (AA-AP) normally range from 115.5 to 147.7 and from -6.2 to 43.0 , with no difference in male and female. The sum of AACC and APCC (AA+AP) normally ranges between 268.6 and 298.4 in male, between 263.9 and 294.4 in female. AACC, ACBM, AA-AC, AA-AP and AA + AP in one male patient and one female patient with BI were 118.5 versus 121.1, 155.8 versus 146.8, -37.3 versus -25.7 , -17.6 versus -23.9 and 254.6 versus 266.2respectively, and the averages of them were obviously different from those of the control group (P<0.0005). The angles of AACC, A C B M and AA-AC in the group of Chiari were 142.3 1.3, 132.2 2.4 and 10.1 2.0, and were different from those of the control group ( 1 50.0 6.6 , 118.9 6.0 and 31.1 10.3 , P<0.05) . There were no differences in APCC, AA-AP and AA + AP between the group of Chiari and the control group. The average angles of the posterior margin of the clivus (APMC) in normal, BI and Chiari groups were 163.2 7.5 162.3 9.0 and 161.0 1.5 , with no significant differences (P>0.6). The average lengths ( x 眘, mm) of the anterior and the posterior margins of the subarachnoid space of the posterior cranial fossa (PCF) in the group of Chiari (AMPCF and PMPCF) (50.0 4.6 and 38.3 7.4) were shorter than those of the normal control group (58.8 5.5, 50.0 5.2,P<0 . 0 1 ) . Con cl us ion The normal ranges of AACC, A C B M , AA-AC, AA-AP, and AA + AP can be used in MRI for the diagnosis of BI. The double negative angles of AA-AC and AA-AP are characteristics of BI of the anterior margin type and the anterior lateral margin type on T2\VI of MRI. The decreased angle of AA + AP and the negative angle of AA-AC are the characteristics of BI of the whole margin type on T 2 W I of MRI. These characteristics can be recognized by naked eyes without measuring the angles, and will be useful in decreasing the rate of missing diagnosis of BI by MRI. The results that the shortened AMPCF and PMPCF in patients with Chiarimalformation support the opinion that overcrowding inthe PCF is the pathogenesis of the disease. |
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