Chiari 1.5 malformation

Case contributed by Dr Antonio Rodrigues de Aguiar Neto


The patient was presenting with posterior headache, nausea and vomiting.

Patient Data

Age: 50 years
Gender: Female

MRI demonstrates elongated and descent of the cerebellar tonsils that extend approximately 11 mm below the foramen magnum along with brain stem (obex) herniation, causing flattening of the medulla anteroposteriorly. The inferior displacement of the cerebellar tonsils measured concerning the McRae line, drawn from the anterior margin (basion) to the posterior margin (opisthion) of the foramen magnum.

There is a dorsal bump at the cervicomedullary junction, and crowding at the foramen magnum due to the descent of cerebellar tonsils.

The osseous abnormalities associated are platybasia (the basal skull measures 145º), basilar invagination (protrusion of the odontoid tip of 7 mm above the Chamberlain line), hypoplastic clivus, retroflexion of the odontoid process.

Case Discussion

Chiari 1.5 malformation is characterized by an inferior herniation of the cerebellar tonsils below the foramen magnum greater than 5 mm in adults (Chiari I) 1,2, in combination with inferior descent of some portion of the brain stem, often the obex of the medulla oblongata (Chiari 1.5) 2,3. In children, the tonsils usually are located below the foramen magnum, and measurements of 7 mm may be usual 1.

Chiari I and 1.5 malformations may be associated with craniocervical osseous anomalies including platybasia, basilar invagination, retroflexion of the odontoid, and short hypoplastic clivus 2,4, all of which may be predictive factors for the formation of syringohydromyelia 4.

This case illustrates the appearance of a Chiari 1.5 malformation, associated with craniocervical osseous anomalies, but without syrinx formation.

Case courtesy

  • Sterfferson Morais, MD - PGY-3, Radiology Resident, Department of Radiology
  • Antonio Rodrigues de Aguiar Neto, MD - Radiologist, Department of Radiology
  •  Hospital da Restauração – Recife, PE – Brazil
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Case information

rID: 70264
Published: 11th Aug 2019
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included
Institution: Real Hospital Português de Pernambuco - Recife, PE - Brazil

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