A morphometric analysis on the correlation between position of cerebellar tonsil and posterior fossa volume in the patients with idiopathic scoliosis

English Keywords:Idiopathic scoliosis  Cerebellar tonsil  Physiological herniation  Posterior fossa volume

English Abstract:

  【Abstract】 Objectives: To compare the posterior fossa volume of idiopathic scoliosis(IS) patients with that of age-matched healthy adolescents and to determine the correlation between position of cerebellar tonsil and posterior fossa volume in IS patients. Methods: A retrospective radiographic study was performed on 500 patients with IS who received surgical treatment at our center between January 2009 and June 2011. 70 IS patients(group A) were selected with the following inclusion criteria: (1)age ranged from 16 to 20 years, and the Risser sign was 5; (2)each patient had a posteroanterior standing X-ray and a combined head and cervical spine MRI scan. Of them, there were 48 males and 22 females. The Cobb angle of scoliosis was 51.2°±14.1°. 58 age-matched healthy adolescents were recruited as controls. Of them, there were 27 males and 31 females. On sagittal MRI images, the position of the cerebellar tonsil was evaluated by the distance(d) between the inferior pole of cerebellar tonsil and the line connecting the basion and opisthion(AB line). And the anteroposterior diameter of the foramen magnum(AB), the length of supraocciput(BC), the anteroposterior diameter of the posterior fossa(CD) and the length of the clivus(AD) were measured on mid-sagittal MRI images to make a comparison of the posterior fossa volume between the IS patients and controls. Then a further analysis was performed to determine whether there was significant difference of the posterior fossa volume between IS patients with(group A1) and without physiological tonsillar ectopia(group A2). Then the correlation between curve magnitude and posterior fossa volume was also investigated in this study. Results: It was shown that the positions of cerebellar tonsil in group A were significantly lower than the positions in group B(P<0.05). The incidence of physiological tonsillar ectopia in IS was found to be 22.9%. Significant increment in anteroposterior diameter of the foramen magnum(AB) was found in group A compared to group B(P<0.05), while significant decrements were found in the three remaining indexes(P<0.05). However, Cobb angles of the main curve in group A were found to be not correlated with positions of cerebellar tonsil. Significant difference in no index but the length of supraocciput(BC) was found in IS patients with physiological tonsillar ectopia(group A1) compared to IS patients without physiological tonsillar ectopia(group A2). Conclusions: The high incidence of physiological tonsillar ectopia in IS patients might be caused by the heteroplasia of posterior fossa, indicating that abnormal growth kinetics of endochondral and membranous ossification could be found in the development of posterior fossa.