Ventricular Catheter Placement via Keen's Point (Parieto-Occipital Approach)
Critical Limitation of This Approach
The parieto-occipital (occipital) approach provides the narrowest margin of error among all ventricular catheter entry points, with only 8° tolerance in the sagittal plane and 11° in the coronal plane, making it the most technically demanding approach that requires patient-specific trajectory planning rather than generic anatomical landmarks. 1
Anatomical Entry Point
Keen's point is located approximately 2.5-3 cm superior and 2.5-3 cm posterior to the pinna of the ear, or approximately 6-7 cm above the inion and 3-4 cm lateral to the midline 1, 2
This entry point targets the atrium or posterior horn of the lateral ventricle, though some surgeons aim for the frontal horn when using this approach 1
Optimal Trajectory Parameters
Sagittal plane angle: The catheter should be directed perpendicular to the skull surface or slightly anterior, with only an 8° margin of error 1
Coronal plane angle: The catheter should be angled toward the medial canthus of the ipsilateral eye, with an 11° margin of error 1
Critical finding: No single generic aiming landmark achieves successful ventricular cannulation in all cases via this approach—generic landmarks succeed in only 86% of attempts 1
Catheter Length Specifications
Optimal insertion depth: The catheter should be inserted to position the tip in the frontal horn near the foramen of Monro when targeting anteriorly, or in the atrium when targeting the posterior horn 3, 4
Length calculation: Pre-operative imaging (CT or MRI) should be used to calculate patient-specific catheter length, as overlong catheters are significantly associated with poor placement outcomes 5
Average measurements: In adults with hydrocephalus, catheter lengths typically range from 100-140 mm depending on ventricular size, with longer catheters (>139 mm) associated with grade 3 (poor) placements 5
Critical Technical Principles
The catheter tip must be surrounded by CSF and avoid contact with choroid plexus, ependyma, or ventricular walls—this is the single greatest predictor of shunt survival (HR 0.21,95% CI 0.094-0.45; p = 0.0001) regardless of entry point 3
Preoperative simulation is strongly recommended: Virtual 3D simulation on workstations improves accuracy dramatically, achieving 100% optimal placement with mean slip angles of only 2.8° compared to 8.6° without simulation 2
Catheters terminating in the atrium show significantly higher rates of proximal occlusion than those in the frontal horn (p < 0.001) 3
Practical Technique Recommendations
Patient-specific stereotactic planning is required for reliable first-pass cannulation via the parieto-occipital approach in adults, as generic guides and surface landmarks are insufficient 1
Smartphone-assisted guides or neuronavigation can improve accuracy when preoperative imaging measurements are incorporated 6
The rectangular (perpendicular) approach in the sagittal plane with individual angle adjustment in the coronal section based on preoperative imaging provides optimal results 6
Common Pitfalls to Avoid
Do not rely on generic anatomical landmarks alone—the parieto-occipital approach has the highest failure rate (14% poor placement) when using surface anatomy without patient-specific planning 1
Avoid excessive catheter length—catheters longer than necessary significantly increase the risk of parenchymal penetration and poor placement 5
Large ventricular size increases placement difficulty—patients with larger ventricles (>22 mm) paradoxically have worse outcomes via this approach, likely due to catheter length miscalculation 5
In infants, be aware that skull growth will alter catheter position over time regardless of initial placement accuracy 3
Alternative Consideration
- The frontal approach offers significantly greater margins of error (42° sagittal, 30° coronal) and may be preferable when preoperative imaging or navigation is unavailable 1