A radiographic analysis of ventricular trajectories

The prevalent method of ventriculostomy placement is via freehand insertion to cannulate the ventricle at a 90° angle to the skull to get ideal placement. Our goal was to test the validity of this practice in patients without midline shift and with normal ventricular size.

This study was a virtual radiographic analysis of 3-dimensional data of skull and ventricular anatomy. Data were collected using thin-cut (1-mm) computed tomography scans of 101 randomly selected patients with normal ventricular anatomy. Virtual ventriculostomy trajectories were determined for entry from the right and left sides separately, going in at a 90° angle to the skull. Three-dimensional multiplanar reconstructions were performed using Osirix software to see where the catheter would end up within the brain.

In our patient population, the mean bicaudate index was 0.14. Of the 202 perpendicular lines created from Kocher's point into the brain, 67.8% (137) of the virtual lines passed through the ipsilateral frontal horn of the lateral ventricle, 20.8% (42) passed through the contralateral ventricle, and 10.4% (21) did not pass through a ventricular space. A lower bicaudate index also leads to a greater misplacement even with a perpendicular trajectory. Pushing a catheter beyond an entry length of 6.5 cm if no cerebrospinal fluid flow has been obtained will not result in ipsilateral ventricular catheterization.

Our study concludes that not all catheters passed through Kocher's point using a perpendicular trajectory will end up in the ipsilateral frontal horn, and almost 10% of these catheters will be in a nonventricular space. In the instance in which a freehand pass fails to cannulate a ventricle, the safest alternative would be to make only minor adjustments to the perpendicular angle.