100 Chiari I Malformation

Mahmoud A. Al Yamany, Homoud Aldahash, and Abdulrahman J. Sabbagh

Fig. 100.1 (A) Sagittal and (B) coronal T2-weighted magnetic resonance images, demonstrating small posterior fossa, descended cerebellar tonsils down to the level of C1–C2 level posteriorly, and compression of the cranio–cervical junction and cervical spinal cord.

Clinical Presentation

A 32-year-old woman presents with a long history of neck pain, intermittent bilateral shoulder pain, worsened with neck flexion and extension and during coughing and/or sneezing.

She also complains of intermittent numbness in the tips of her fingers bilaterally.

On physical examination, she has no neurologic deficits.

Her past medical history is remarkable for an operation as a child for scoliosis, which was corrected at the age of 13 years. She did not have any further problem in that regard.

Magnetic resonance imaging (MRI) is obtained and shown in Fig. 100.1.

Questions

What is the differential diagnosis?
What does the sagittal image of the MRI demonstrate?
Describe your management.
What is the expected outcome?
What are the possible complications of this procedure?

Assume this patient presented with progressive difficulty walking and spasticity. If she also presented with a spine MRI showing a syrinx in the upper thoracic and lower cervical cord, what would be your answers to the following questions?
What is the best management for the syrinx?
What are the pathogenesis theories of syringomyelia in Chiari I malformation?
Would you expect radiologic or clinical improvement to occur first?
How long would you wait before you expect the syrinx to start narrowing?
What are the different types of Chiari malformations?

Answers

What is the differential diagnosis?

Differential diagnosis includes
- Hydrocephalus
- Chiari malformation with cervical spinal cord syrinx
- Isolated cervical spinal cord syrinx following scoliosis surgery
- Cervical spine spondylosis
- Tumors of the cervicomedullary junction or cervical spine

What does the sagittal image of the MRI demonstrate?

Sagittal MRI of the brain demonstrates
- Small posterior fossa
- Descended cerebellar tonsils, below the level of the craniocervical junction
- Secondary myelomalacia of the cervical spinal cord

Describe your management.

Management consists of suboccipital craniotomy.
- Removing the rim of the foramen magnum and the posterior arch of C1
- This is followed by duraplasty, with or without arachnoid lyses and/or tonsillar resection.

What is the expected outcome?

The expected outcome would be a stabilization of symptoms or arrested symptom progression.

There is a chance of improvement in her neurologic condition and a good chance of improvement of the headache and neck and shoulder pain.1–3
What are the possible complications of this procedure?
- Possible complications of the procedure include the following⁴:
  - Cerebrospinal fluid (CSF) leak
  - Subdural hygroma
  - Wound infection
  - Further herniation of the tonsils due to raised intracranial pressure
  - There is a small chance of intraoperative neural tissue injury.
  - Postoperative headache – causes include chemical meningitis from the patch or glue
  - Possibility of nocturnal respiratory depression following posterior fossa manipulation (more common in Chiari type II)
What is the best management for the syrinx?
- First line of management is treating the Chiari malformation via a suboccipital decompression¹ (see answer of Question 3 for details).
- Alternative options include adding a syringosubarachnoid shunt after the Chiari decompression in selected cases (presence of a large syrinx, with significant thinning of the spinal cord tissue and obliteration of the spinal subarachnoid space, especially when combined with syrinx-related symptoms),⁵ or syringopleural shunt.
What are the pathogenesis theories of syringomyelia in Chiari I malformation?
- Several theories exist:
  - Gardner’s hydrodynamic theory⁶:
    - First to recognize the frequent association of syringomyelia with Chiari I malformation
    - Delay in the perforation of the roof of the rhombencephalon
    - Subarachnoid space does not fully open.
    - CSF becomes trapped in ventricular system.
    - The exaggerated pulsations are directed into the central canal causing hydromyelia.
  - Williams theory⁷
    - Postulated and later confirmed that such an obstruction could act as a valve, allowing CSF to cross the foramen magnum rostrally more effectively than caudally
    - Craniospinal dissociation is described where CSF may be “sucked” from the 4th ventricle into the central canal.
  - Ball and Dayan theory⁸
    - Activities that increase thoracic or abdominal pressure such as coughing and straining causes the spinal CSF to be diverted into the spinal cord parenchyma along dilated Virchow–Robin spaces.
  - Aboulker theory⁹
    - Spinal CSF enters into the cord by way of the dorsal root entry zone.
    - Absorption occurs either by
      - Blood vessels of the spinal gray matter
      - Rostral drainage through the central canal into the 4th ventricle
  - Oldfield theory^10,11
    - The force that pushes spinal subarachnoid CSF into the cord parenchyma is the CSF pulsation pressure occurring during the cardiac cycle.
    - This pulsation will drive CSF into the cord along perivascular spaces.
  - Other theories such as Greitz¹² (intramedullary pulse pressure theory)
    - Suggests that syringomyelia is caused by increased pulse pressure in the spinal cord and that the syrinx consists of extracellular fluid rather than CSF
Would you expect radiologic or clinical improvement to occur first?
- Expect to see improvement in clinical symptoms before radiologic improvement.
How long would you wait before you expect the syrinx to start narrowing?
- The radiologic improvement in the width of the syrinx is expected within the first 3–6 months, but continued narrowing of the syrinx may take years.
- According to Wetjen et al.’s series of 29 patients with syringomyelia and Chiari I malformations, the average diameter of the syrinx preoperatively is ~6.9 mm (with a 2.1 mm standard deviation), whereas postoperatively it is less than 1.5 mm at last evaluation (p < 0.0001).
- The median time for the syrinx narrowing is 3.6 months after a Chiari decompression is completed.11
What are different types of Chiari malformations?
- There are four types of Chiari malformations.¹³
- See Fig. 100.2 for details of each of the three main types.
- Note that Chiari type IV includes cerebella hypoplasia.¹³