Chiari I Malformation · Posterior Fossa Decompression Indications

Step-by-step decision

Choose step by step as prompted; reaching an endpoint gives the management recommendation. You can go back a step or restart anytime.

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Full pathway

1. [Decision] Symptoms/syringomyelia + degree of descent
   Symptoms or syringomyelia? Degree of tonsillar descent? (Tonsillar descent ≥5 mm is the imaging criterion, but whether to operate depends on symptoms and syringomyelia, not the millimeters of descent alone.)
   • Symptomatic (classic cough/strain-induced occipitocervical pain, brainstem/cerebellar/cord signs) or with syringomyelia → Symptomatic/syrinx → posterior fossa decompression
   • Asymptomatic, no syringomyelia (incidental) → Asymptomatic no syrinx → observe
2. [End] Symptomatic/syrinx → posterior fossa decompression
   Symptomatic or with syringomyelia → posterior fossa decompression: suboccipital craniectomy + C1 (C2 if needed) laminectomy to relieve foramen magnum crowding; whether to open the dura for expansile duraplasty is individualized (a syrinx/arachnoid adhesions favor opening, improving syrinx resolution but with slightly more complications); the syrinx usually resolves after decompression.
3. [End] Asymptomatic no syrinx → observe
   Asymptomatic, no syringomyelia → observe + follow-up MRI; imaging descent alone is not a surgical indication; reassess for decompression if symptoms or a new syrinx appear.

Source guidelines & references

• Chiari I malformation surgical management (neurosurgical consensus; tonsillar descent ≥5 mm is only an imaging criterion, must combine symptoms and syrinx)

This pathway is our own synthesis of the decision logic in the guidelines above (not the guideline verbatim); thresholds and workflows change as guidelines update — in practice follow the latest guideline, your institution's protocol and the individual patient.

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