Morphometric and Topographic Features of Stylomastoid Foramen and its Clinical Significance in Facial Nerve Block

Objective  This study aims to determine the topographic localization of the stylomastoid foramen (SF) and its morphometric relationship with the surrounding bony landmarks. Design  A descriptive anatomical study. Setting  Anatomy Laboratory of the Faculty of Medicine. Participants  Measurements were performed on 53 dry temporal bones. Main Outcome Measures  On the inferior and lateral aspects of photographic images, lines and angles were defined. The most lateral end of the SF (SF1) and the transverse medial-lateral line that passes through the upper end of the anterior border of mastoid process (line 1) were used as reference points for topographic evaluation. The upper end of the anterior border of mastoid process (A) and the tip of mastoid process (B) were considered in defining angles. The dates about SF were evaluated using the ImageJ 1.46r software and digital caliper. Results  SF1 was classified into three different types based on its topographical localization, stated as Type 1, Type 2, and Type 3. In Type 1, SF1 was located anterior to line 1 (54.7%). SF1 was located posterior to line 1 in Type 2 (34.0%). SF1 was located just over line 1 in Type 3 (11.3%). We also detected angular variations between these types in the inferior and lateral aspects. Conclusion  The recommended angles of application are 30 degrees on the horizontal plane and 55 degrees on the sagittal plane for Type 1 when point B is considered. A needle length below 10 mm is more suitable to minimize the potential complications of the nerve block.