How is the classification of Chiari malformations?
Chiari malformations classification is based on the morphology of the malformations and includes seven separate entities: - Chiari I malformation, characterized by descent of the caudal tip of cerebellar tonsils through the foramen magnum greater than 5 mm; - Chiari 1.5 malformation (a variant of Chiari I), which is characterized by herniation of the cerebellar tonsils, in combination with inferior descent of the brain stem; - Chiari II malformation, represented by herniation of the cerebellar tonsils greater than 5 mm past the foramen magnum, the brainstem, and the fourth ventricle, usually associated with lumbosacral spinal myelomeningocele; - Chiari III malformation, which is similar to Chiari II associated with a posterior occipital or high cervical encephalocele; - Chiari IV malformation, characterized by cerebellar hypoplasia/aplasia with normal posterior fossa and no herniation of the cerebellum through the foramen magnum; - Chiari V malformation, characterized by absent cerebellum and herniation of the occipital lobe through the foramen magnum; - Chiari 0 malformation, which is a controversial term, characterized by syrinx without cerebellar tonsillar or brain stem descent.
Concerning Chiari malformations types, which is the most common type?
Chiari I is the most common type, 1 in 1000 births, and it is prevalent in females.
What is the difference between Chiari I and Chiari 1.5 malformations?
Chiari I malformation is characterized by a caudal descent of the cerebellar tonsils through the foramen magnum > 5 mm, and Chiari 1.5 is characterized by herniation of the cerebellar tonsils (Chiari I), in combination with inferior descent of some portion of the brain stem, often the obex of the medulla oblongata.
What are the common symptoms of Chiari I and Chiari 1.5 malformations?
The most common symptoms are posterior headaches or neck pain. Other symptoms are vertigo, tinnitus, nystagmus, paresthesias, cerebellar ataxia, spasticity, and problems related to cranial nerves in the brain stem, which may include weak vocal cords, trouble swallowing, and breathing issues.
What is the best diagnostic test in Chiari malformations?
The best diagnostic test in Chiari malformations is MRI.
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.