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

Abstract

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. Conclusions 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.

Evaluation of the Morphometry of the Stylomastoid Foramen in the Turkish Population: A Retrospective Study Using Cone-Beam Computed Tomography (CBCT)

“…mastoid process, the jugular surface, and the stylopharyngeus muscle. SMF lies between the mastoid process and the base of the styloid process of the temporal bone [1,2,3]. The SMF is the terminal portion of the facial canal (FC) and is the exit gateway of the facial nerve from the skull base [2,[4][5][6].…”

“…Information on the morphometry of the SMF and FC is of great importance to surgeons and anesthesiologists in a variety of procedures to avoid neural complications [1,2]. SMF's anatomical variations may be a risk factor resulting in unilateral facial nerve palsy or Bell's palsy [4].…”

“…Morphometric studies on SMF and FC were performed using dry adult skulls [1][2][3][4]7,[10][11][12][13], three-dimensional models [14], medical computed tomography (CT) [8,15,16], and magnetic resonance imaging (MRI) [17] up to date. Cone beam computed tomography (CBCT) which is increasingly used in dentistry today, has the potential to become the main imaging method for the temporal bone and adjacent structures.…”

“…the literature about the morphometry of the SMF and FC to provide information for the Nadbath block [2,7].…”

“…These previous studies were managed with CT, MRI, three-dimensional models, and dry adult human skulls on the anatomy and the morphometric features of the SMF and FC [1][2][3][4]7,8,[10][11][12][13][14][15][16][17]. Although CT is the primary imaging technique of the temporal bone, the concept of CBCT seems particularly appropriate for high-density structures.…”