Arnold-Chiari, malformation

Group of malformations of the neuraxis including the brainstem, the cerebellum, the 4th ventricle and the cervical spine.

Different types:

-         type I: coning of the cerebellar tonsils (more than 5 mm below the foramen magnum at MRI). 
This anomaly can be associated with:

-         cervical spinal dysmorphism: stretching, kinking, hydromyelia, hydrocephalus

-         syndromic craniosynostosis, including Crouzon (70%) or Pfeiffer (50%) syndromes due to the hypoplasia of the posterior part of the skull, causing also a compression of the respiratory centers  and an obstruction to cerebral venous return; in these cases, occipital decompression may correct the associated central sleep apnea syndrome.

-         intracranial hypotension due to leakage of CSF: in these cases, repair of the leak corrects the x-ray picture and the symptoms of intracranial hypotension.

-         type II: generally associated with a meningomyelocele; displacement  of the vermis, the 4th ventricle, the bulb and the lower part of the pons into the cervical canal

-         type III: associated with an occipital encephalocele

-         type IV: severe (rare) cerebellar hypoplasia associated with a meningomyelocele


Anesthetic implications

swallowing problems and risk of inhalation of pharyngeal or gastric contents. Risk of paralysis of the vocal cords (stridor). Breathing disorders during sleep:  obstructive and/or central (often undiagnosed) apnea. Risk of intracranial hypertension (most often, a ventriculoperitoneal shunt is present ). In  case of meningomyelocele: risk of latex allergy.

In case of type I, flexion of the neck moves the cerebellum tonsil downwards (1,4 mm on average). It can block the flow of CSF and cause intracranial hypertension and compression of nerve structures. Extension of the neck has a reverse effect, which may explain the spontaneous position in opisthotonos in some patients.  That must be taken into account for laryngoscopy and positioning of the head during a procedure.


References : 


Updated: February 2018