MR morphometric study and its clinical significance in syringomyelia Chiari I malformation

Objective To investigate the pathogenesis of the syringomyelia in Chiari I malformation by measuring the posterior cranial fossa structures. Methods The posterior cranial fossa structures on mid sagittal MR image were measured in 50 normal subjects,and 24 Chiari I malformation patients associated with syringomyelia and 26 Chiari I malformation patients without syringomyelia. The t test was used for statistical analysis. Results In Chiari I malformation patients and normal subjects, the width of the CSF space anterior to the medulla oblongata was (4 2±1 8) mm and (6 6±1 4) mm respectively( t =7 30, P 0 01). The brain skull ratio of Chiari I malformation group was larger than normal subjects( t =7 33, P 0 01), there was no significant difference in the size of posterior brain between the two groups( t =0 28, P 0 05). In Chiari I malformation with syringomyelia group and without syringomyelia group, the width of the CSF space anterior to the medulla oblongata was (2 9±1 4) mm and (5 5±1 1) mm respectively( t =7 30, P 0 01). In Chiari I malformation with syringomyelia group, the width of the medulla oblongata and the tonsil of cerebellum was wider than in the control group,the width of the CSF space posterior to the tonsil of cerebellum was narrower than control group. The location of the medulla oblongata was significantly lower than in the control group. There was no significant difference in the morphology of posterior cranial fossa between the two groups. Conclusion The overcrowding in the posterior fossa and the froamen magnum region, and the compression on the junction of medulla oblongata with the spinal cord could influence the circulation of cerebrospinal fluid and may lead to the development of syringomyelia. The MRI measurement of the posterior cranial fossa structures is very useful in the treatment and prognosis of the Chiari I malformation.