Chiari Malformations
-The Chiari malformation is a term
encompassing a range of hindbrain maldevelopments.
-Problems include underdevelopment
of the cranial fossa and overcrowding of the normally developed hindbrain, the
risks of descent of hindbrain structures below the foramen magnum, and
intermittent obstruction to CSF outflow from the fourth ventricle.
-There may be a relatively high CSF
pressure in the head and a relatively lower one in the spine.
Types of Chiari Malformations:
There are four types.
Type I:
-Downward herniation of cerebellar
tonsils of at least 3–5 mm below the foramen magnum and hindbrain overcrowding
results in direct compression of the tissue.
-Clinical symptoms thus relate to
CSF disturbances and direct compression of nervous tissue; they include
headaches, pseudotumor-like episodes, a syndrome resembling Meniere’s disease,
lower cranial nerve signs, and spinal cord disturbances without syringomyelia.
-It is mostly seen in young adults.
Type II (Arnold–Chiari):
-It is the most important and
includes; thoracolumbar myelomeningocele, hypoplasia of the posterior fossa, and
displacement of the cerebellar vermis, brainstem, and fourth ventricle.
-It presents in infancy or early
childhood.
Type III: rare
-Dilated the fourth ventricle with
cervical meningomyelocele.
Type IV: rare
-Cerebellar hypoplasia.
Other abnormalities:
1. May be associated with
syringomyelia or syringobulbia, other skeletal abnormalities of the skull base and
cervical vertebrae, or myelomeningocele. Syringomyelia is the term for an
expanding, longitudinal cystic cavity within the spinal cord. In the communicating
variety, there is continuity between the syrinx and the CSF in the central
canal.
2. May need decompression of foramen
magnum or cervical spine.
3. Progressive hydrocephalus may
occur which needs shunt surgery.
4. Obstructive sleep apnea.
5. Recurrent pulmonary aspiration.
6. May exhibit abnormal autonomic
control.
7. Patients may present with
respiratory arrest.
8. Sudden unexpected death may
occur.
Anesthetic Problems:
1. Increased ICP may lead to coning.
2. Symptoms may start after a dural
puncture.
3. Bolus injections into the
epidural space may lead to ICP increases in susceptible individuals.
4. Sleep apnea may occur in Chiari
type I.
5. Acute cardiovascular collapse
secondary to inadvertent brainstem compression in an infant.
Anesthetic Management:
1. A careful history should be taken
in a patient with a ventriculoperitoneal shunt, to check for any signs that it
is nonfunctioning. If there is doubt, a referral to a neurosurgeon is indicated.
This is particularly important if the notes are absent, there is poor
history or lack of follow-up.
2. Try to prevent anything likely to increase ICP, such as coughing, or hypercarbia from heavy sedation or
analgesia.
3. Avoid straining in labor.
Epidural anesthesia for Cesarean section was performed in a patient with type I
Chiari who had a previous difficult tracheal intubation. Small doses of local
anesthetic should be titrated gradually, to avoid sudden distension of the
epidural space or decreases in arterial pressure.
4. Spinal anesthesia should be
avoided.
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