Best Imaging for Chiari Malformation
MRI of the brain without contrast, including sagittal T2-weighted sequences of the craniocervical junction, is the required imaging study for suspected Chiari malformation. 1
Primary Imaging Modality
MRI is mandatory for accurate diagnosis and assessment of Chiari malformation, providing optimal visualization of cerebellar tonsillar position relative to the foramen magnum and associated soft tissue abnormalities. 1
CT is not appropriate as an initial imaging modality for evaluating suspected Chiari malformation and should not be used for this purpose. 1
If CT is performed incidentally (e.g., during trauma evaluation) and suggests tonsillar descent, confirmation with dedicated MRI is required before assigning any clinical significance to avoid unnecessary surgical intervention. 1
Essential MRI Protocol Components
Mandatory Sequences
Sagittal T2-weighted sequences of the craniocervical junction are mandatory to evaluate cerebellar tonsillar position relative to the foramen magnum. 1
These sagittal images are the most informative and demonstrate abnormalities of the telencephalon, diencephalon, mesencephalon, rhomboencephalon, and upper spinal cord extremely well. 2
Optional Advanced Sequences
Phase-contrast CSF flow studies at the craniocervical junction may be added to assess CSF flow obstruction, which is the primary mechanism of symptom generation in Chiari malformation. 1, 3
Phase-contrast MRI can measure peak velocities at the anterior cervical 2-3 (AC2-3), posterior cervical 2-3 (PC2-3), and aqueduct levels, with pre-surgery PC2-3 cranial peak velocity >2.63 cm/s and aqueduct cranial peak velocity >2.13 cm/s predicting primary symptom improvement after surgery. 3
Gradient echo or susceptibility-weighted sequences should be included to fully evaluate the extent of the malformation. 1
Comprehensive Evaluation
Complete brain and spine imaging is recommended to evaluate for associated conditions such as hydrocephalus or syringomyelia, which occur in approximately 70% of Chiari I patients and influence management decisions. 1, 4
MRI allows classification of Chiari malformation into Type A (with syringomyelia, 70% of cases) and Type B (without syringomyelia, 30% of cases), which has prognostic and clinical relevance. 4
Clinical Correlation Requirements
Imaging findings must be correlated with characteristic symptoms—most notably Valsalva-induced occipital headache that worsens with coughing or straining—to establish a definitive diagnosis. 1, 5
Look specifically for suboccipital headache, diplopia, neck pain, vertigo, nystagmus, or central cord symptoms (in Type A with syringomyelia) versus brainstem or cerebellar compression symptoms (in Type B without syringomyelia). 1, 4
Common Pitfalls to Avoid
Do not rely on CT alone even in emergency settings; while CT may be performed first for rapid exclusion of hemorrhage or mass effect, definitive evaluation of Chiari malformation still requires subsequent MRI. 1
Do not operate on incidental tonsillar ectopia discovered on imaging performed for unrelated conditions (global headache, cervical radiculopathy) without confirming that symptoms are truly related to the Chiari malformation, as this unnecessarily places patients at risk of operative complications. 6
Be aware that Chiari 0 malformation (tonsillar ectopia <5 mm with syringomyelia) responds similarly to surgical decompression as Chiari I and should not be excluded from treatment based solely on the degree of tonsillar descent. 6