Arnold-Chiari syndrome without spina bifida or hydrocephalus

This code identifies a congenital malformation of the brain, specifically a downward displacement of the cerebellar tonsils through the foramen magnum, without the presence of spina bifida or hydrocephalus. This structural abnormality can compress the brainstem and spinal cord, leading to various neurological symptoms.

Use this code for patients diagnosed with Arnold-Chiari malformation Type I, where imaging studies confirm cerebellar tonsillar herniation but explicitly rule out co-occurring spina bifida or hydrocephalus. Documentation should clearly state the absence of these associated conditions.

• Ensure documentation specifies "Type I" or explicitly states the absence of spina bifida and hydrocephalus.
• Do not use this code if spina bifida or hydrocephalus are present; instead, refer to codes for Arnold-Chiari with those associated conditions.
• Always review imaging reports (MRI, CT) and neurologist's notes for definitive diagnostic statements and exclusion criteria.