Volumetric changes and anomalies in MRI in patients with chiari malformation

Objective: The aim of our study was to measure the total, supratentorial (ST) and infratentorial (IT) intracranial volumes using Cavalieri Method; examine the anomalies as well as tonsillar herniation and their distribution; measure foramen magnum diameter, posterior cranial fossa (PCF) volume, several cranial distances and angles required for evaluation of platybasia using magnetic resonance (MR) images of patientes with Chiari Malformation Type 1. We aimed at clarifying whether the volume difference between the compartments or congenital anomalies are more significant regarding etiology of CM by comparing our findings and retrospectively formed control group.Material and Method: 33 patients with CM Type 1, symptomatic or asymptomatic, aged between 20-65 years, having no intracranial space occupying lesions and 33 control subjects were included in our study. In sagittal MR images, tonsillar herniation length and concurrent anomalies were evaluated; ST, IT and total intracranial volumes were measured using Cavalieri Method; several cranial distances and angles used for evaluation of platybasia and PCF development were measured. Results obtained from control group and CM Type 1 group were analyzed statistically. Comparisons and relations between groups were assessed.Results: Tonsillar herniation and concurrent anomalies: Tonsillar herniation length below foramen magnum was 9,091±3,392 mm in CM Type 1 group. Tonsillar herniaton was mild in 66,7?%, moderate in 24,2% and severe in 9,1% of the patients. Tonsillar herniation and concurrent syringomyelia, concavity and defect of clivus, herniation of bulbus and fourth ventricle, basilar invagination and craniovertebral junction anomaly rates were found to be 30,3%, 27%, 18,2%, 3% and 3%, respectively. Absence of cisterna magna was encountered in 87,9% of CM Type 1 cases. Intracranial volume Measurements: In control group total, IT and ST intracranial volumes were 1358±101,9 ml, 184,3±22,91 ml ve 1174±90,01 ml, respectively. Total, IT and ST intracranial volumes were 1272±145,6 ml, 167,4±23,79 ml ve 1104±125,8 ml in patient group. All of the three parameters were significantly decreased in the patient group. Distance and angle measurements: Distance measurements used for evaluation of platybasia including the distance between Chamberlain line and tip of dens axis, Klaus index, clivus length, distance between internal occipital protuberance and opisthion were significantly decreased in the patient group. Welcher basal angle and Boogard angle were found to be increased, tentorial slope was found to be decresed.Conclusion: Significant decrease is observed in total, IT and ST intracranial volumes in CM Type 1. Especially IT intracranial volume decrease is prominant in the patients. Thus, tonsillar herniation with normal IT volume suggests other possible underlying causes. Absence of cisterna magna, syringomyelia and craniovertebral junction anomalies frequently accompany tonsillar herniation. Regarding the findings, we think that congenital anomalies are important in CM type 1.