Surgical Technique for Ventricular Catheter Placement in VP Shunts
Both frontal and occipital-parietal entry points are acceptable options for ventricular catheter placement, as there is insufficient evidence to recommend one over the other; however, the most critical factor for shunt survival is ensuring the catheter tip is surrounded by CSF rather than touching brain parenchyma or ventricular walls. 1
Entry Point Selection
Standard Entry Points
The two most commonly employed entry points are:
- Frontal approach (Kocher's point): Located approximately 1-2 cm anterior to the coronal suture and 2-3 cm lateral to midline 1
- Occipital-parietal approach (Keen's point): Located posterior to the coronal suture 1
Age-Specific Considerations
In infants, the occipital entry point may be advantageous due to skull and brain growth effects on final catheter position. 1 Frontal entry in infants results in higher degrees of ventricular catheter shortening and burr hole migration with growth, potentially causing suboptimal placement over time even if initially optimal. 1
In adults, Keen's point (occipital-parietal) demonstrates superior accuracy, with 65% correct localization compared to other approaches, and is the only independent predictor for optimal catheter position (adjusted OR 0.04; 95% CI: 0.01-0.67). 2
Trajectory and Target
The ventricular catheter should most often terminate in the frontal horn, away from the choroid plexus, though the atrium or occipital horn may be targeted occasionally. 1 However, catheters terminating in the atrium show significantly higher rates of proximal occlusion than those in the frontal horn (p < 0.001), with differences primarily occurring during the first year after insertion. 1
Critical Technical Principle: Catheter Tip Position
The environment surrounding the catheter tip is the greatest predictor of shunt failure, regardless of entry location. 1
Optimal Positioning Criteria
- Catheter tip surrounded by CSF: Provides significantly improved shunt survival (HR 0.21,95% CI 0.094-0.45; p = 0.0001) compared to tips surrounded by brain parenchyma 1
- Avoid contact with: Choroid plexus, ependyma, glial tissues, or ventricular walls 1
- Suboptimal catheter tip position is the only independent determinant for shunt revision (adjusted OR 0.11; 95% CI: 0.01-0.98) 2
Measurement Techniques
For Frontal Approach (Kocher's Point)
When using a guiding protractor for patients with bicaudate index >0.2 or bifrontal distance >25 mm:
- Ideal guiding angle ranges from 17-23° (mean 19.6° ± 1.6°) relative to the horizontal head axis 3
- This angle should be determined from coronal CT or MRI images preoperatively 3
For Parieto-Occipital Approach
Use patient-specific craniometrics and skull landmarks rather than fixed measurements to account for variations in skull shape and size. 4 This technique achieved grade 1 positioning (free floating in CSF) in 64% of cases and grade 2 (touching choroid plexus or wall) in 36%, with no parenchymal placements. 4
Technical Adjuncts
Image Guidance Options
While most ventricular catheters continue to be placed without technical adjuvants 1, several options exist:
- Ultrasound guidance: Increases rate of optimally placed catheters (67% vs 49% freehand, p = 0.28) and eliminates malpositioned shunts (0% vs 5.8% freehand) 5
- Frameless stereotaxis: Can be used for patients with smaller ventricles 3
- Freehand technique: Remains acceptable when proper anatomical landmarks and angles are used 1
Common Pitfalls
Avoid fixed measurement approaches that don't account for individual patient anatomy, as skull shape and size variations significantly affect accuracy. 4
In infants, frontal entry requires awareness that growth will alter catheter position over time, potentially necessitating earlier revision even with initially optimal placement. 1
Right-sided access is a predictor for accurate localization (OR 0.4; 95% CI: 0.1-0.9), suggesting preferential use of the right side when clinically appropriate. 2