Analysis of a Novel Entry Point for Freehand Ventriculostomy Using Computerized Tomography Scans

Abstract

Background External ventricular drain (EVD) placement is one of the most common procedures in neurosurgery. Neurosurgeons generally prefer to access the ventricles via Kocher's point since it is the most common point of entry to this area; however, this point is used to describe different anatomic landmarks and is not well-defined. Objective The present study aims to describe and provide an anatomical assessment of a novel ventriculostomy access point developed by the authors using computerized tomography (CT) scans performed on 100 patients. Materials and methods Data were collected from 100 randomly selected patients with normal ventricular anatomy found on their 1.0 mm-slice CT scans performed at the Burdenko Neurosurgical Center from March 2019 to June 2021. The CT inclusion criteria were: CT slices < or = to 1 mm and absence of brain herniation. Patients with brain mass lesions, severe brain edema, and pneumocephalus were excluded. Age, gender, and ventricular size were not exclusion criteria. Results The mean patient age was 43.58 years (range 4-73), with 50 men and 50 women. The mean Evan's index was 25.7 % (SD=4.38 %, range 10.2-41.0 %). No differences were found between the angles of EVD placement on either side (89.50±1.22 degrees on the right and 89.60±1.14 degrees on the left). Hence, nearly all EVD cases had been placed perpendicularly to the skull surface at a pinpoint location. Conclusion The proposed point of successful ventriculostomy placement in this study was 3 cm from the bregma along the coronal suture. The angle of EVD placement was approximately 90 degrees in almost all patients and was independent of the patient's age and the side of the head that was entered. Little correlation was found between the value of the entry angle and Evan's index. The point is simply identifiable, and its entry is easily accessible in practice.

Keywords: anatomical; ct; evd; freehand; hydrocephalus.

Figure 1. Entry point and EVD placement angle measurements on CT scan

A, axial slices; B, trajectory of EVD insertion in the sagittal plane; C, trajectory of EVD insertion in the frontal plane; D, 3D reconstruction imaging depicting the point of trephination on the skull surface EVD = external ventricular drain; CT = computed tomography

Figure 2. Case example of EVD placement

A, B, C - Case example of an EVD placement at a point along the coronal suture 3 cm from the bregma; D – schematic illustration of EVD placement at the proposed point EVD = external ventricular drain

Figure 3. Density plot (A) and Q-Q plot (B) depicting the distribution of Evan’s index in the overall group

Figure 4. Regression line between the entry angle and Evan's index and their respective density plots