How should an adult with symptomatic Arnold‑Chiari (Chiari I) malformation presenting with occipital headache worsened by Valsalva, ataxia, dysphagia, vertigo, or progressive myelopathic signs be evaluated and managed?

Management of Symptomatic Chiari I Malformation in Adults

For an adult presenting with symptomatic Chiari I malformation (occipital headache worsened by Valsalva, ataxia, dysphagia, vertigo, or progressive myelopathy), posterior fossa decompression surgery is indicated, as these symptoms represent clear neurological dysfunction requiring intervention. 1

Diagnostic Evaluation

Essential Imaging Studies

• Obtain MRI with sagittal T2-weighted sequences of the craniocervical junction to confirm cerebellar tonsillar herniation ≥3-5 mm below the foramen magnum and assess neural compression 1, 2
• Perform complete brain and spine imaging to evaluate for associated conditions including hydrocephalus (present in 15-20% of Chiari I patients), syringomyelia (present in 60% of symptomatic patients), and basilar invagination 1, 3, 4
• Add phase-contrast CSF flow studies to evaluate for CSF flow obstruction at the foramen magnum, which is a primary pathophysiological mechanism causing symptoms 1, 2

Clinical Assessment Focus

• Document the presence of strain-related or Valsalva-induced headaches, as these are the cardinal symptom most likely to improve with surgical decompression 1, 2
• Evaluate for lower cranial nerve dysfunction manifesting as dysphagia and dizziness, which indicates direct brainstem compression 1
• Assess for myelopathic signs including ataxia, peripheral motor and sensory defects, clumsiness, and abnormal reflexes 1
• Screen for respiratory irregularities in severe cases, as central apneas can occur with significant brainstem compression 1

Special Diagnostic Considerations

• Rule out pseudotumor cerebri syndrome when cerebellar tonsillar ectopia >5 mm is identified, to avoid misdiagnosis 1
• Consider myelography with CT if MRI findings are equivocal or to identify focal regions of CSF obstruction that may be amenable to surgical intervention 5

Surgical Management

Indications for Surgery

Surgery is definitively indicated for your patient given the presence of neurological dysfunction (ataxia, dysphagia, vertigo, progressive myelopathy) and symptomatic strain-related headaches. 1, 3

Surgical Options

• Either posterior fossa decompression (PFD) alone or posterior fossa decompression with duraplasty (PFDD) are acceptable first-line surgical options, with both carrying Grade C recommendations from the Congress of Neurological Surgeons 1
• Dural patch grafting (duraplasty) may potentially improve syrinx resolution rates if syringomyelia is present 1
• Cerebellar tonsil resection or reduction may be performed during PFD to improve syrinx and/or symptoms, with Grade C recommendation 1

Goals of Surgery

• Relieve brainstem compression and cranial nerve distortion to address dysphagia, vertigo, and myelopathic symptoms 5
• Restore normal CSF flow across the foramen magnum to alleviate headaches and prevent progression 2, 5
• Reduce the size of any associated syrinx cavity if present 5

Management of Associated Syringomyelia

If syringomyelia is present on imaging:

• Wait 6-12 months after initial surgery before considering reoperation if the syrinx persists, as this is a Grade B recommendation from the Congress of Neurological Surgeons 1
• Understand that symptom resolution and syrinx resolution do not correlate directly—patients may improve symptomatically without complete syrinx resolution 1
• Consider additional neurosurgical intervention at 6-12 months only in patients without radiographic improvement 1

Special Considerations and Pitfalls

Craniocervical Instability

• Evaluate for craniocervical instability, which may require decompression and/or fusion of the craniocervical junction in addition to standard decompression 1

Associated Conditions

• If hydrocephalus is present (15-20% of cases), consider ventriculoperitoneal shunting first, as this may resolve symptoms and alleviate the need for Chiari decompression in some patients 3
• Document associated osseous abnormalities including scoliosis (25%), basilar invagination (12%), increased cervical lordosis (8.5%), and Klippel-Feil syndrome (3.3%) 4

Prognostic Expectations

• Strain-related headaches have the best surgical outcome, with the highest likelihood of improvement after decompression 1, 2
• Other symptoms (ataxia, dysphagia, vertigo, myelopathy) demonstrate more variable response to decompression surgery 1
• Long-term prognosis is variable and depends on presenting symptoms and spinal cord cyst response 3

Critical Safety Issues

• Avoid chiropractic manipulation, as Chiari I symptoms may be aggravated by such interventions 6
• Recognize that Chiari I is associated with deaths following minor trauma and acute respiratory failure, making timely diagnosis and treatment essential 6