Mine was at 20mm and I was starting to show signs of paralysis when mine was discovered, so I was rushed to surgery
. I only knew of the existance of Chiari for 3 weeks before my surgery
, some people may be diagnosed and watched for years, even decades, before they need surgery.
Type 2 and beyond are often noticable at birth. They often causes partial or complete paralysis below the spinal defect and generally have noticable malformed brains at least on an MRI.