Entrapped 4ᵗʰ ventricle

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Hydrocephalus (HCP)

General

• Aka: isolated fourth ventricle

Definition

• 4ᵗʰ ventricle that neither communicates with
• The 3ʳᵈ ventricle (through Sylvian aqueduct) NOR
• The basal cisterns (through foramina of Luschka or Magendie).

Aetiology and mechanism

1. Chronic shunting of the lateral ventricles, especially with (Occurs in 2–3% of shunted patients)
• Post-infectious hydrocephalus (esp: fungal) → obstruction of the foramina of Luschka or Magendie, or infective debris pooling in the basal cisterns
• Repeated shunt infections
• CSF diverted from flowing down the normal channels → the aqueduct collapses → prolong apposition of the ependymal lining → adhesion formation

2. Dandy walker malformation: if the aqueduct is also obstructed

3. The choroid plexus of the 4th ventricle continues to produce CSF → enlarges the ventricle

Clinical presentation

• Headache

• Lower cranial nerve palsies: swallowing difficulties

• Pressure on the floor of the 4ᵗʰ ventricle may compress the facial colliculus → facial diplegia and bilateral abducens palsy

• Ataxia

• Reduced level of consciousness

• Nausea/vomiting

• May also be an incidental finding
• May have “atypical” findings: reduced attention span

Treatment

• Treatment entrapped 4ᵗʰ ventricle may also alleviate associated slit ventricles

• Shunting ventricle with a separate VP shunt or linking into an existing shunt options
• Insertion from below the tonsils under direct vision.
• Catheter brought out at the dural suture line,
• Catheter anchored at dural suture line by use of an angle adapter sutured to the dura
• 1ˢᵗ choice
• Passage through a cerebellar hemisphere
• Potential complications
• Delayed injury to the brainstem by the catheter tip as the brainstem moves into its normal position with drainage of the 4ᵗʰ ventricle.
• This may be avoided by bringing the catheter into the 4ᵗʰ ventricle at a slight angle through the cerebellar hemisphere
• Torkildsen shunt (ventriculocisternal shunt)
• Must ensure that arachnoid granulations are functional
• Usually not the case with hydrocephalus of infantile onset
• Image is for lateral ventricle not 4ᵗʰ ventricle

• An LP shunt may be considered when the 4th ventricle outlets are patent

• Endoscopic aqueductoplasty (EA) with and without stenting
• The burr hole for EA is placed more anteriorly than the one for standard ETV.
• Stenting of the aqueduct may be performed for patients at high risk for aqueductal restenosis or patients with a trapped 4ᵗʰ ventricle.
• The stent is usually a ventricular catheter with additional holes.
• If patient have slit ventricles (because of shunt)
• Poor candidates for the standard EA
• Can try suboccipital approach for retrograde aqueductoplasty and stenting
• Pros
• Restores the physiologic CSF pathways
• Eliminates the risk for basilar artery injury.
• The risk for injuring the hypothalamus is avoided, especially during cases when the floor of the 3ʳᵈ ventricle is thickened and a considerable amount of force is required to perforate the floor.
• Strictures at the aqueduct are usually not as tough to penetrate; thus, less force is required for fenestration.
• Cons/complications
• Injuring the periaqueductal gray matter and the floor of the 4ᵗʰ ventricle.
• If there is a long stenoses,
• Can cause
• Midbrain injury causing transient or permanent dysconjugate eye movements,
• Parinaud-syndrome,
• Cranial nerve palsies.
• Try ETV instead

Complications

• Cranial nerve palsies
• Due to
• Penetration of the brainstem by the catheter,
• At the time of catheter insertion OR
• A delayed fashion as the 4ᵗʰ ventricle decreases in size
• Overshunting causing traction on the lower cranial nerves as the brainstem shifts posteriorly