Validation of Härtel Surface Anatomical Landmarks for Locating the Foramen Ovale: A Computed Tomography Scan Analysis and Revised Technique Description.

Background and objectives: Härtel triangle provides surface landmarks for locating the foramen ovale (FO) when performing trigeminal nerve percutaneous procedures. Although widely adopted in clinical practice, there is no report that these landmarks have ever been formally validated through modern imaging techniques. Here we aim to validate Härtel anatomical landmarks using computed tomography scans and propose technical considerations for percutaneous trigeminal procedures.

Methods: Retrospective analysis of 198 FO from 99 adult head computed tomography scans. Measurements included distances from FO to external auditory canal (EAC), FO to midline, eye's midpupillary (MP) line to midline, and eye's inner canthus (IC) line to midline. Statistical analysis was performed, and results were compared with Härtel description.

Results: The mean distance from EAC to FO was 23.26 mm (SD: 3.00 mm). Distance from midline to FO was 25.43 mm overall (SD: 1.87 mm). Distance from midline to MP line was measured at 31.96 mm (SD: 1.89 mm). The mean distance from midline to IC line was 14.68 mm (SD: 1.73 mm).

Conclusion: Härtel landmarks can be adjusted for greater accuracy when performing percutaneous trigeminal nerve procedures. The FO is located closer to the EAC and more medially situated than previously assumed. Revised technique suggests aiming the needle trajectory approximately 2 to 2.5 cm anterior to the tragus and targeting a point between the IC and MP lines rather than directly along the MP line. Excessive medial and posterior needle displacement should be avoided to prevent inadvertent vascular injury. These adjustments could enhance procedural accuracy and safety, improving patient outcomes.