# Revisiting Härtel’s technique for percutaneous transoval glycerol injection

## TL;DR

This study revisits a technique for a medical procedure used to treat trigeminal neuralgia and identifies better entry points and paths for the needle to improve outcomes.

## Contribution

The study identifies optimal anatomical landmarks for needle guidance in percutaneous transoval glycerol injection to improve treatment outcomes.

## Key findings

- The optimal entry point is located 2 mm below the mouth angle and in front of the mandibular ramus.
- Meckel’s cave is accessible through the medial part of the foramen ovale from this entry point in most cases.
- Improved technical results can be achieved by selecting the right entry point and minimizing cheek tissue movement.

## Abstract

Percutaneous transoval glycerol injection (GI) has been widely used since 1981 in the treatment of patients with trigeminal neuralgia. However, outcomes have been more variable than with other percutaneous treatments. Although most authors state that they use Härtel’s technique, the variations are numerous—which may explain procedural problems and most of the poor results. The aim of the present imaging-based study, therefore, was to revisit Härtel’s technique and identify optimal landmarks for guiding the needle from the cheek to Meckel’s cave.

Eleven patients referred for trigeminal neuralgia were studied. We used CT- and MRI-based simulations to determine the optimal entry points in the cheek and trajectories through foramen ovale (FO) to reach Meckel’s cave – and compared our findings with the results from Härtel’s original study.

The optimal entry point was located at 2 mm below the horizontal plane through the angle of the mouth and just in front of the anterior edge of the mandibular ramus. From this entry point—situated around 10 mm below Härtel’s preferred entry point—Meckel’s cave was easily accessible through the medial part of FO in 17 of 22 sides.

The findings from this study suggest that the technical results of transoval glycerol injection can be improved if we 1. Select the optimal entry point, 2. Guide the needle under fluoroscopy through the medial part of the foramen ovale, and 3. Minimize movement of the soft tissues in the cheek.

The online version contains supplementary material available at 10.1007/s00701-025-06526-3.