Overview
This lecture reviews surgical decision-making for posterior fossa decompression, focusing on techniques, risks, and materials used to treat conditions like Chiari malformation, particularly in pediatric patients.
Surgical Decision Points in Posterior Fossa Decompression
- Posterior fossa decompression always includes bone removal and C1 laminectomy.
- Key decision: whether to open the dura (outer membrane covering the brain and spinal cord) or just thin it.
- Opening the dura (duroplasty) is more effective at reducing syrinx (spinal cyst) size.
- Duroplasty increases risk of complications such as cerebrospinal fluid (CSF) leak.
- Without syrinx, avoiding duroplasty can lower complication risk; with syrinx, duroplasty is favored for better radiological outcomes.
- Decision depends on balancing symptom improvement, imaging, and complication risk.
Evidence and Outcomes
- Single-center and meta-analysis studies show similar rates (10-12%) of needing repeat surgery, whether for persistent symptoms without duroplasty or complications with it.
- Clinical symptom improvement is similar regardless of initial approach.
- Ongoing studies (e.g., Park Reeves trial) aim to clarify which patients benefit most from each approach.
Intra-Dural Assessment and Procedures
- If dura is opened, inspecting for CSF flow through the obex (exit of fourth ventricle) is recommended.
- Arachnoid veils blocking CSF flow may require removal to prevent surgical failure.
- Additional procedures like tonsil reduction are optional to prevent future scar-related narrowing.
- Historical use of stents and canal plugs are now rarely applied as first-line treatments.
Dural Closure and Patch Materials
- Primary dural closure (simply sewing up) is uncommon; patches increase space post-decompression.
- Patch options include autograft (patient's own tissue), allograft (from another source), animal-derived, or synthetic.
- Autograft (typically pericranium) results in fewer complications like pseudomeningocele (fluid collection) and chemical meningitis.
- Bovine pericardium is a safer non-autograft alternative compared to synthetic options.
Alternative Surgical Approaches and Controversy
- C1-C2 fusion (spinal fusion of neck vertebrae) proposed as an alternative for all Chiari cases, but increases surgical risks and reduces neck mobility.
- Majority of pediatric neurosurgeons prefer posterior fossa decompression over routine C1-C2 fusions.
Key Terms & Definitions
- Dura — tough outer membrane covering the brain and spinal cord.
- Duroplasty — surgical opening and patching of the dura.
- Syrinx — a fluid-filled cyst within the spinal cord.
- CSF (Cerebrospinal Fluid) Leak — escape of fluid from the subarachnoid space post-surgery.
- Pseudomeningocele — abnormal CSF collection under the skin after surgery.
- Autograft — tissue graft from the patient's own body.
- Allograft — tissue graft from a donor or animal source.
Action Items / Next Steps
- Review outcomes of ongoing randomized trials (e.g., Park Reeves) once data are published.
- For surgical cases, ensure intraoperative assessment of CSF flow if dura is opened.
- Consider autologous pericranial patch as first-line material for dural closure when possible.