Introduction of Universal WON-Point for Posterior Cranial Fossa Puncture in Monitoring Infratentorial Intracranial...

Intracranial pressure (ICP) monitoring is a gold standard in brain injury management. While supratentorial ICP monitoring is widespread, monitoring in the posterior cranial fossa is rare and lacks a standardized location. To define and validate a novel anatomic reference point-the WON point-for minimally invasive and standardized infratentorial ICP (iICP) probe placement.

The WON point was defined as the outer third toward the ear along a line connecting the center of the external auditory canal on the side of ICP probe placement to the mastoid tip on the contralateral side. Feasibility was first assessed in 11 patients undergoing neuronavigated surgery. The point was marked and validated using tip extension. Next, an ICP sensor was implanted in 14 adult body donors on both sides. Depth, distances to venous sinuses (transverse, sigmoid, occipital, jugular bulb), and damage to critical structures were assessed. Finally, the WON point was used for iICP monitoring in 3 patients with ischemic cerebellar infarction.

The WON point proved safe and effective. No damage to adjacent critical structures such as the brainstem was observed. The median distances from the WON Point were to transverse sinus 2.25 cm (IQR 1.8-2.5), to occipital sinus 4.15 cm (IQR 3.3-4.5), and to sigmoid sinus 3.2 cm (IQR 2.8-3.4). The safe median distance to the nearest venous structure was 3.28 cm (IQR 3.0-3.4).

The universal WON point is a novel anatomic landmark enabling safe and reliable iICP monitoring through minimally invasive sensor placement, with cadaveric and radiological analyses confirming a consistent safe zone and 3 pilot clinical cases demonstrating feasibility in real patients. Further clinical validation is warranted to standardize its use in neurosurgery.