Chiari 2 is congenital and involves a herniation of the cerebellar tonsils, herniation of the lower part of the brainstem (the medulla oblongata), the fourth ventricle, an incomplete/missing/herniated vermis (the nerve tissue that connects both halves of the cerebellum) AND the corpus callosum (nerve fibers connecting both hemispheres of the brain) is fully/partially absent (agenesis). Most patients with Chiari 2 have a myelomeningocele (the most severe form of Spina Bifida), hydrocephalus, and/or Tethered Cord Syndrome. Approximately 90% of those with a myelomeningocele have Chiari 2.
OBSTACLES IN DIAGNOSIS/TREATMENT: While diagnoses of the myelomeningocele usually happens at birth (or in utero), the displaced tonsils are often not diagnosed until symptoms develop later in life, usually in childhood (as opposed to Chiari 1 where symptoms usually develop in early adulthood). The myelomeningocele is usually surgically addressed in infancy, as well as hydrocephalus that often accompanies this form of Spina Bifida.
Treatment Options: Studies show that < 10% of Chiari 2 patients are decompressed. Among younger patients < 1 year of age, studies show that there is a higher prevalence with complications of tracheostomy and/or gastrostomy, since most of the surgical procedures associated with a myelomeningocele patients are conducted in infancy, this may contribute to the decline in those having decompression surgery, however many adults with Chiari 2 are simply told that they are not candidates with no explanation given or that their case is too complex and/risky for decompression.