Rare diseases · Sign or symptom
Chiari type I malformation
HP:0007099
What it means
Arnold-Chiari type I malformation refers to a relatively mild degree of herniation of the posteroinferior region of the cerebellum (the cerebellar tonsils) into the cervical canal with little or no displacement of the fourth ventricle. It is characterized by one or both pointed (not rounded) cerebellar tonsils that project 5 mm below the foramen magnum, measured by a line drawn from the basion to the opisthion (McRae Line)
Rare diseases that can present with this21
Common30–79%
4Sometimes5–29%
13- 19p13.13microdeletion syndrome
- Autosomal dominant hyper-IgE syndrome due to STAT3 deficiency
- Brachydactyly-short stature-retinitis pigmentosa syndrome
- Contractures-developmental delay-Pierre Robin syndrome
- Glossopharyngeal neuralgia
- Gorham-Stout disease
- Macrocephaly-intellectual disability-left ventricular non compaction syndrome
- Proximal 16p11.2 microdeletion syndrome
and 5 more in this range
The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Arnold Chiari type I malformation · Arnold-Chiari type I malformation · Chiari I malformation
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Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.