Best Imaging for Syrinx in Chiari Malformation
MRI of the complete spine without IV contrast is the imaging study of choice for evaluating a syrinx associated with Chiari malformation. 1, 2
Primary Imaging Recommendation
Complete spine MRI is mandatory—not optional—for all patients with Chiari malformation undergoing initial evaluation, regardless of whether surgery is planned. 1, 3 The Congress of Neurological Surgeons explicitly recommends that patients diagnosed with Chiari I malformation on brain or cervical spine MRI alone should undergo further imaging of the entire brain and spine to evaluate for clinically relevant pathology such as syrinx or hydrocephalus. 1
Key Technical Requirements
Sagittal T2-weighted sequences are the essential sequences for visualizing both the syrinx cavity and the cerebellar tonsillar position relative to the foramen magnum. 2, 4
No IV contrast is required for routine syrinx evaluation in Chiari malformation—the syrinx fluid is clearly visible on T2-weighted imaging without gadolinium. 1, 2
Phase-contrast CSF flow studies at the craniocervical junction may be added to assess CSF flow obstruction, which is a primary mechanism of symptom generation, though this is optional rather than mandatory. 2, 4
Why Complete Spine Imaging Matters
Isolated thoracic syrinx occurs in 4.5% of all Chiari patients and 9.1% of those with any syrinx—and cannot be predicted clinically. 3 A study of 266 children with Chiari malformation found that demographic variables, clinical presentation, and extent of tonsillar ectopia showed great heterogeneity, with no clinical factor consistently associated with isolated thoracic syrinx. 3 This means cervical-only imaging will miss nearly 1 in 10 syrinx cases.
Clinical Implications
Syrinx location influences surgical decision-making and technique selection. 3, 5
The presence of syrinx—even if asymptomatic—may influence the decision to operate in symptomatic Chiari patients. 3
Follow-up imaging interpretation depends on knowing the full extent of the syrinx at baseline. 6, 5
Role of CT and Other Modalities
CT has no role in syrinx evaluation. 2 The American College of Radiology states that CT is not appropriate for evaluating suspected Chiari malformation, and even when CT incidentally suggests tonsillar descent, confirmation with dedicated MRI is required before assigning clinical significance. 2
CT myelography may be considered only in specific scenarios: when MRI shows findings suspicious for arachnoid cyst, arachnoid web, or ventral cord herniation requiring further characterization. 1 However, this is a problem-solving tool after MRI, not a primary imaging modality.
Common Pitfalls to Avoid
Do not order brain-only or cervical-only MRI for initial Chiari evaluation—you will miss isolated thoracic syrinx in approximately 1 in 22 patients. 3
Do not add IV contrast routinely—it provides no additional information for syrinx evaluation and adds unnecessary cost and risk. 1, 2
Do not rely on symptom severity to predict syrinx size—symptoms attributed to spinal cord damage have no significant relationship to syrinx size on MRI. 6
Do not assume cervical symptoms mean cervical-only disease—25-85% of children with Chiari have syrinx, and location does not always correlate with symptom distribution. 3
Follow-Up Imaging Considerations
For postoperative monitoring, the same complete spine MRI protocol should be repeated. 6, 5 Syrinx size reduction on MRI does not reliably correlate with symptom improvement—patients may experience marked clinical relief even when the syrinx persists radiographically. 4, 6 This is important for realistic postoperative counseling but does not change the imaging recommendation.