Chiari Malformations

Types of Chiari Malformation

Type I Chiari Malformation

• The most common and least severe type
• Characterized by protrusion of one or both cerebellar tonsils 5 mm past the foramen magnum
• Results in a change of CSF flow at the level of the foramen magnum, which can subsequently result in the development of syringomyelia1
• Incidence is 0.5-3.5 percent of the population¹
• Symptoms vary:
  • It may be asymptomatic until adolescence or adulthood, or may be found incidentally on imaging studies.
  • Occipital headaches that are worsened by Valsalva maneuvers, such as coughing or sneezing
  • Other symptoms include neck pain, dizziness or balance problems, muscle weakness, vision problems, or dysphagia.
  • The presence of a syrinx may result in upper extremity deficits, including numbness, weakness, or loss of pain/temperature sensation.
  • Central apnea may also occur.

Type II Chiari Malformation

• Also known as Arnold Chiari malformation
• In addition to herniated cerebellar tonsils, Type II also includes herniation of the medulla and cerebellar vermis into the foramen magnum.
• Type II Chiari malformations are often associated with lumbosacral myelomeningoceles.

Type III Chiari Malformation

• Involves herniation of cerebellar tonsils, cerebellum, brain stem and fourth ventricle and an occipital or high cervical encephalocele

Type IV Chiari Malformation

• Rarest type
• The cerebellum fails to form, resulting in cerebellar hypoplasia or complete absence, associated with other severe brain malformations.
• Life expectancy is less than 1 year.

PFD

• The main surgical goal is to alleviate symptoms or control symptom progression by relieving compression and restoring CSF flow.
• After positioning the patient prone, a skin incision is made, and the surgeon dissects through the neck muscles, obtaining exposure of the skull base and the top of the spine.
• The surgeon then performs a suboccipital craniectomy and possibly a laminectomy at the C1 level.
• An ultrasound is then performed intraoperatively to determine if there is enough widening of the foramen magnum to restore normal CSF flow.
• If CSF flow is not improved, the surgeon may perform a duraplasty, opening the dura and placing a dural patch to seal the area.
• A Valsalva maneuver may be requested of the anesthesiology team to assess for any leaks after dural closure.

Preoperative Planning

• A detailed history and physical examination should be performed. Clinician should focus on the patient’s neurologic status and document any history of neurological symptoms and findings of deficits on examination.
• An airway plan should be developed and advanced airway equipment should be available in case of difficult intubation.
• The surgical plan should be discussed with the team, including the need and type of neuromonitoring to be utilized for the procedure.
• The plan for intraoperative and postoperative pain management should be discussed; this may include intraoperative posterior cervical nerve block, local administration by the surgeon, and possibly postoperative patient-controlled analgesia.
  • A case series of ultrasound-guided greater occipital nerve blocks found these blocks to be easy to learn and perform and demonstrated no significant adverse effects.²
  • The use of multimodal analgesics such as intravenous acetaminophen or nonsteroidal anti-inflammatory drugs should be considered to minimize the use of opioid medications and their undesirable side effects.

Intraoperative and Postoperative Care

• Either inhalation or intravenous induction may be used, depending on the patient’s age, maturity, or medical comorbidities.
• Airway management: consider maintaining a neutral neck position for intubation, depending on the patient’s cervical anatomy and neurologic symptoms.
• The risk of intraoperative endotracheal tube displacement or kinking with prone positioning should be considered; nasotracheal intubation or a reinforced endotracheal tube should be considered to mitigate this risk.
• Invasive monitoring with an arterial line should be considered. The decompressive procedure itself, located in the posterior fossa of the brain, does not involve significant manipulation of critical structures; hence, one would not expect sudden swings in hemodynamics or significant blood loss. However, if the patient has comorbidities in which an arterial line could provide useful clinical information, one should be placed for safety.
• Anesthetic maintenance drugs should be tailored based on the type of neuromonitoring used. This is often surgeon- and case-specific, but may include somatosensory evoked potentials, electromyograms, or both.
• Excessive patient movement or bucking should be avoided on emergence. Barring intraoperative complications, the patient can be extubated at the conclusion of the case.
• Postoperative disposition is institution-specific. The patient may recover on the hospital floor or in the intensive care unit. This should be determined by the hospital’s capabilities for serial neurological examinations, as deemed by the neurosurgery service.

Postoperative Complications and Disposition

• Surgical results are reported to be excellent in Chiari malformation type I, with 78% improvement/resolution of syringomyelia, 75% improvement in neurological status, and 81% improvement or resolution of suboccipital headaches.¹
• Benzon et al. found a low rate of intraoperative anesthesia complications (8.4%) in children who underwent PFD for Chiari I malformation. Those included bradycardia, hypertension, hypotension, issues with the endotracheal tube, such as kinking or mainstem intubation, loss of neuromonitoring signals, and oversedation.³
• Younger children and those with ASA class >2 or an intraoperative anesthesia complication are associated with increased risk of unanticipated admission to the intensive care unit.³
• Massive macroglossia is a rare but potentially life-threatening complication of posterior fossa surgery. Postoperative intubation may be needed due to airway obstruction. Potential causes may be mechanical trauma, lymphatic or venous congestion, or neurogenic lingual edema.⁴