A MR Morphometric Study And Pathogenestic Investigation On Chiari Type â…  Malformation

Background and purpose: Chiari type I malformation isa serious congenital disease which is characterized by a downwardherniation of more than 5 mm of cerebellar tonsils,which wasconsidered to be a primary neurological anomaly involving thehindbrain and spinal cord in the past.Although there has been manyhypothesis about its cause,its accurate pathogenesis is stillunAnown.Rescent c1inical and experimental studies indicate that thetonsillar heniation observed in Chiari type I malfOrmation couldresult from overcrowding within a primary small and shallowposterior cranial fossa due to an underdeveloped occipital somiteoriginating from the paraxial mesoderm.The objective of our studyis to investigate the morphological changes of the skull and4$Nk$2002 $$kfe1 Chiari I ffi*SMMN6Ate$k,Wk&t6MMmttintracranial structures by means of MRJ and to determine thepossible pathogenesis of Chiari type I malformation, at the sametime,to analyze the method of measurement.MateriaIs and Methods: A measurement of the posteriorcranial fossa structures on the mid-sagittal MRJ was carried out in27 cases of Chiari type I malformation without hydrocephalusand other skul1 base anomalies between January l994 to October200l at our hospital.As a control,40 normal subjects were also.investigated by the means of an image processing software.Thestructures of the brain and skull were investigated on mid-sagittalT1-weighted MR images(Siemens l.0-tesla)which was obtaintedusing a repetition time of 500 to 600 msec and an echo time of 20 to25 msec.The t-test was used for statistical anslysis.Results: Comparing to the control group,there was asignificantly larger brain-skull ratio(P<0.0l)and a smallerbasioocciput-clivus ratio(P<0.0l)of the posterior fossa among thepatients who suffered from Chiari type I malformation.In the'mean time,the posterior fOssa-total cranial volume ratio was alsosmaller among the patients(P<0.05).A significant differencebetween the Chiari group and the controI group in some of themain angle degrees of posterior cranial fossa was alsorevealed(P<0.05).Conclusion: (l)An underdeveloped occipital bone with2002 fegjkifejt Chiari Inormally developed neural structures, inducing overcrowding in the posterior cranial fossa,may play an important role in the cause of Chiari type I malformation.(2)It should be reasonable to choose the ratio of different structures in itself instead of place reliance on the absolute measure values when morphometric studies were performed. (3 )It seems reliable to take the place of the irregular cranial area with the value of the length multiplying the width in such studies. (4)The authors believe that MRI and image processing software may be of great usefulness in the appreciation of the morphological changes of the skull as well as brain abnormalities.