Hi Tonsillar ectopia, encompassing slight descent of the cerebellar tonsils and Chiari I malformations, are disorders observed routinely in older children and adults and are believed to be an acquired form of the Chiari malformations Chiari malformations defect in the area of the back of the head where the brain and spinal cord connect If the Cerebellar tonsils increase in size they may put pressure on another part of the brain called medulla oblangata which passes through the skull opening Suggest do not neglect the condition and consult another neuro surgeon for second opinion and if required he may suggest for repeat MRI Wish You Good Health Regards Dr Sridhar K