| BackgroundBecause of the deep location of the lesions in the ventral of the foramen magnum and lower clivus and the adjacent to the important structures such as brainstem,vertebrobasilar artery and cranial nerve,the operation in this area is difficult and risky.Scholars at home and abroad have tried many approaches to this area.At present,the far lateral approach is considered to be the ideal surgical approach to remove the lesions in this area.Undoubtedly,the occipital condyle is the most concerned in the far lateral approach.It is not only an important bone to maintain the stability of the craniocervical junction,but also has an impact on the surgical field of vision and operation space.Scholars at home and abroad have done a lot of researches on whether or not to remove the occipital condyle and its range,but there is no uniform standard at present.Because of the common anatomic variation of occipital condyle,its shape and size may vary from person to person,so it is necessary to understand the morphological measurement of occipital condyle in detail,which is helpful to make the plan for the treatment of occipital condyle during operation.ObjectiveTo understand the length,width and thickness of occipital condyle by measuring the anatomical parameters of occipital condyle in CT images of normal adult head and neck.Materialise’s Interactive Medical Image Control System(Mimics)was applied to reconstruct the visualized three-dimensional model of the occipital condyles.The surgical visual fields were measured in the far lateral approach included the occipital condyle not removed and the occipital condyle removed from the posterior edge of the occipital condyle to the internal orifice of the hypoglossal nerve canal.The distance between the posterior margin of the occipital condyle and the posterior edge of internal orifice of hypoglossal nerve canal was measured.The differences of the correlation anatomical parameters of occipital condyle between different sides and sexes were analyzed.It can provide anatomical basis for the treatment of occipital condyle in the far lateral approach.MethodsThe imaging data of 335 normal adults with head and neck CT in the imaging database of the first affiliated Hospital of Xinxiang Medical University from September 2018 to March 2019 were analyzed retrospectively.The length of the occipital condyle(anteroposterior axial length),the width of the occipital condyle(the widest lateral diameter)and the thickness of the occipital condyle(the lower margin of the internal orifice of hypoglossal nerve canal and the lower margin of the occipital condyle)were measured at the sagittal position,the horizontal position and the coronal position of the bone window image.The three-dimensional image of the reconstructed occipital condyle was adjusted by the software of mimics in the norma basilaris,and the location points were selected respectively by the coordinate axis.These location points include the midpoint of anterior edge of foramen magnum(A)、the midpoint of posterior edge of foramen magnum(B)、the posterior edge of occipital condyle and posterior edge of foramen magnum(C)and the midpoint of posterior edge of internal orifice of hypoglossal nerve canal(D).∠α is the angle between the line connecting point A and point B and the line connecting point A and point C.The surgical visual field was observed when the occipital condyle was not removed in the far lateral approach.∠β is the angle between the line connecting point A and point B and the line connecting point A and point D.The surgical visual field was observed when the occipital condyle was removed from the posterior edge of the occipital condyle to the internal orifice of the hypoglossal nerve canal.The length between point C and point D is the distance between the posterior margin of the occipital condyle and the posterior edge of internal orifice of hypoglossal nerve canal(HC).It represents the depth of the hypoglossal canal.The difference between ∠β and ∠α is the enlarged angle after the length of the CD is grinded.Measuring ∠α,∠β and the length CD on both sides,and calculating the difference between ∠β and ∠α.The paired sample t-test was used to compare the differences of the above measurements between different sides and sexes.Results 1.Measurements between different sidesThe length of occipital condyle was(21.59±2.28)mm on the left and(21.55±2.08)mm on the right.The width of occipital condyle was(11.05±1.68)mm on the left and(11.16±1.75)mm on the right.The thickness of occipital condyle was(9.21±1.40)mm on the left and(9.18±1.63)mm on the right.∠α is 42.12°±2.88° on the left and 42.00° ±3.59° on the right.∠β is 59.37°±5.24° on the left and 57.66°±5.39° on the right.The difference between ∠β and ∠α is 17.24°±4.13° on the left and 15.66°±3.87° on the right.The length of CD is(9.14±1.39)mm on the left side and(8.73±1.23)mm on the right side.2.Measurements between different sexesThe length of occipital condyle was(22.15±2.30)mm in male and(20.90±1.92)mm in female.The width of occipital condyle was(12.56±1.43)mm in male and(10.89±1.02)mm in female.The thickness of occipital condyle was(9.92±1.35)mm in male and(8.61±1.03)mm in female.∠α is 42.56°±3.27° in male and 41.55°±3.09° in female.∠β is 58.76°±5.38° on in male and 58.19°±5.35° in female.The difference between ∠β and ∠α is 16.18°±4.17° in male and 16.63°±4.11° in female.The length of CD is(9.20±1.41)mm in male side and(8.72±1.27)mm in female.Comparison of 335 patients between different sides: there were no significant differences in length,width and thickness of occipital condyle and ∠α between different sides(all P were > 0.05).The measured values of ∠β,the difference between∠β and∠α,the length of CD on the left side were higher than those on the right side,and the differences were statistically significant(all P values were < 0.05).Comparison of 335 patients between different sexes: the length,width and thickness of occipital condyle,∠α and the length of CD in male were greater than those in female,the differences were statistically significant(all P values were < 0.05);There were no significant differences in ∠β and the difference between∠β and∠α between different sexes(all P were > 0.05).Conclusions1.There are differences in anatomical measurement data of normal occipital CT images between different sides.The bone from the posterior edge of the occipital condyle to the internal orifice of the hypoglossal nerve canal is removed in the far lateral approach,and the surgical field and enlarged visual angle on the left side are larger than those on the right side.For the ventral median lesion of the occipital foramen,a larger exposure range may be obtained from the left craniotomy.2.The length,width and thickness of the occipital condyle,the distance between the posterior edge of the occipital condyle and the posterior edge of the internal orifice of the hypoglossal nerve canal,the angle between the line of the posterior edge of the occipital condyle and the midpoint of anterior edge of foramen magnum and the sagittal plane were generally larger in male than in female.When dealing with the occipital condyle,we need to consider the differences between different sexes. |
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