The Anatomy of the Stylohyoid Chain: A Systematic Review with Meta-Analysis

Background: The temporal bone's styloid process (SP) is an important structure that extends from the skull base to the parapharyngeal space. The stylohyoid ligament (SHL) attaches it to the hyoid bone. The SP and SHL are considered the stylohyoid chain (SHC) components. The SP's close relationship with vital head and neck structures has important clinical implications. Specifically, SP and SHC variants are linked with clinical conditions. Therefore, adequate knowledge of these variations is of paramount importance. Methods: Using the latest guidelines, a systematic literature review was performed in four online databases (PubMed, Google Scholar, Scopus, and Web of Science) to identify studies referring to the SP's typical anatomy and possible SHC morphological variants. The meta-analysis was conducted using R programming software to calculate the prevalence of typical anatomy and possible variants and the pooled mean length of the SP. Results: A total of 104 studies were included, with a total sample of 136,010 heminecks. The typical SP (under 30 mm) was estimated to have a pooled prevalence of 74.97%. SP elongation was observed in 25.03%. The subgroup analysis identified significant differences based on the study type, with computed tomography (CT) studies having the highest pooled prevalence. The SP length was calculated to have a pooled mean of 28.91 mm. For SHC ossification, the pseudo-articulated type was identified to have a pooled prevalence of 4.39%, and that of the segmented type was detected to be 3.89%. The geographical distribution and study type affected the estimated pooled prevalence. Conclusions: The current evidence-based systematic review with meta-analysis investigated the SHC's typical anatomy and possible variants. The elongated SP pooled prevalence of 25.03% indicates that it is not a rare variant, and CT is the optimal method to investigate such a variant. These details demonstrated by the current meta-analysis could be of importance for clinicians.