Posterior Fossa Volume Measuring Linear And Clinical Significance Of Adult Chiari Malformation Type Associated With Syringomyelia

Objective:The correlation between the linear volume of posterior fossa and the patho-genesis of adult Chiari malformation type I with syringomyelia was studied by measuring the linear volume parameters on posterior fossa MRI in adult patients with syringomyelia.Method:A retrospective analysis was made of the patients with Chiari malformation type I who were admitted to Xuanwu Hospital of Capital Medical University from August 2015 to December 2016 in the spinal cord group of neurosurgery.The criteria for admission were over 25 years old.The patients with Chiari malformation type I accompanied by or without syringomyelia were confirmed by head and neck MRI examination.The patients with unstable craniocervical junction were excluded because of intracranial and intraspinal tumors and scoliosis.56 cases of secondary Chiari malformation caused by hydrocephalus caused by craniocerebral trauma met the above criteria.They were divided into two groups:group A and group B.There were 30 cases in group A.They were Chiari malformation type I with syringomyelia,group B,26 cases in group B.They were Chiari malformation type I without syringomyelia.In the control group,60 normal persons matched in age and sex were selected to exclude the patients with secondary Chiari malformation type I and skull base bone destruc-tion caused by intracranial and intraspinal space occupying lesions,scoliosis and hydrocephalus after craniocerebral trauma.There were 35 males and 21 females in group A and B,aged 28 to 62 years,with an average age of 44 years.There were 32 males and 28 females in the control group,aged 26 to 60 years,with an average age of 43.5 years.The markers(A.anterior median foramen magnum;B.posterior median foramen magnum;C.intraoccipital protuberance;D.dorsal saddle apex,vertical intersection of E.A point to CD)were labeled by craniocerebral MR(Fig.1).The parameters of linear volume of posterior fossa were measured: sagittal dia-meter of occipital foramen magnum(AB),length of clivus(AD),supraoccipital distance(BC),sagittal diameter of posterior fossa(CD),height of posterior fossa(AE).The slope inclination angle a was divided into two groups according to whether or not there was syringomyelia(group A: patients with Chiari mal-formation type I with syringomyelia;group B: patients with Chiari malformation type I without syringomyelia)and control group.The relationship between the linear volume characteristics of posterior cranial fossa and syringomyelia formation was analyzed.Result:The CD value of adult Chiari malformation type I patients with syringe-myelia was76.6(+4.2 mm),AE value was 26.2(+3.5 mm)and angle a was 44.9(+7.8 degrees)lower than that of pure adult Chiari malformation type I patients with 81.4(+7.2 mm),AE value was 32.6(+4.2 mm)and angle a was 49.8(+6.5 degrees).This indicated that the volume of posterior cranial fossa in group A was smaller than that in group B.(2)The AB values of adult patients with Chiari malformation type I and pure Chiari malformation type I were 32.3(+6.3 mm),33.1(+5.6 mm),AD values were 36.4(+2.8 mm),35.9(+3.7),a angle 44.9(+7.8 degrees),49.8(+6.5 degrees)were significantly lower than those of the control group,AB values were 47.3(+6.3 degrees),AD values were 42.4(+6.5)and a angle 58.8(+4.3),which indicated that the volume of cranial fossa in patients with Chiari malformation type I was significantly lower than that in the control group.Conclusion:The volume of posterior fossa in adult patients with Chiari malformation type I is significantly reduced,and smaller volume of posterior fossa may be an important factor associated with syringomyelia.