Case Overview
A 63‑year‑old woman presented with a 5‑month history of right‑sided occipital headaches and neck pain triggered by Valsalva maneuvers. She had a 2‑year history of migraines controlled with propranolol and sumatriptan.
Noncontrast CT showed mild posterior fossa effacement without hemorrhage. MRI revealed bilateral cerebellar subdural hygromas (max 6 mm) and 5 mm tonsillar herniation. Angiography confirmed a Cognard type IV dural AV fistula fed by middle meningeal and occipital arterial branches with cortical venous drainage.
Neurologic exam was unremarkable: intact cranial nerves, normal strength/sensation, no ataxia or papilledema.
This is only the second reported Chiari I malformation associated with a dural AV fistula—and the first type IV lesion.
Key Points
- 63‑year‑old female with Valsalva‑exacerbated occipital headaches
- Bilateral subdural hygromas (6 mm) and 5 mm tonsillar descent
- Cognard type IV posterior fossa dural AV fistula
- Single‑stage fistula obliteration, decompression, hygroma drainage
- Durable occlusion and symptom resolution at 6 months
Surgical Technique
- General endotracheal anesthesia; prone on radiolucent frame
- 12 cm midline incision from inion to C2; harvest pericranial graft
- Suboccipital craniectomy (3 × 4 cm) and C1 laminectomy
- Three burr holes over fistula drainage vein; neuronavigation & NIR vein finder (Figure 7)
- Dura opened circumferentially; devascularize fistula; coagulate and divide arterialized veins
- Chiari decompression: durotomy, arachnoid adhesiolysis, CSF drainage of hygromas
- Dural closure with pericranial graft & fibrin sealant; replace bone flap with titanium plates
- Layered muscle/fascial and skin closure without complications
Innovation Highlight
Figure 7: Near‑infrared vein finder used to detect engorged vein; precise site of fistula marked by white arrow.
Clinical Outcome
- ICU transfer; extubated without issue
- Discharged to rehab on POD 5 for gait training
- Neurologically intact at 2‑week visit; headaches resolved
- 3‑month angiogram: complete fistula occlusion
- 6‑month MRI: resolution of hygromas and tonsillar herniation
Clinical Significance
Single‑stage combined vascular and decompressive approach yields durable anatomical correction and symptom relief.
Discussion & Significance
Only one prior case (Dufour et al.) described an acquired Chiari I from a temporobasal AV fistula (Cognard type III). This is the first type IV case.
Venous hypertension in the posterior fossa disrupts CSF dynamics, causing tonsillar descent—mechanism similar to vein of Galen malformations.
Single‑stage comprehensive surgery addresses all pathologies, reducing need for re‑operation.
Recommend follow‑up angiography at 3 months and MRI at 6 months for surveillance.
Clinical Pearls
- Consider dural AV fistula in atypical Chiari with hygromas
- Use neuronavigation & NIR vein finder for safe resection
- Combine decompression & hygroma drainage
- Obtain angiography at 3 months & MRI at 6 months
