Oral Cavity Lesion Mimicker: How prevalent is the Mylohyoid Boutonnière on MRI?

Background And Purpose The mylohyoid muscle is commonly considered a continuous muscular sling, but it is frequently discontinuous, forming mylohyoid boutonnières that can contain salivary tissue, fat, blood vessels, or lymph nodes. While some studies have explored mylohyoid boutonnières in cadavers and through CT imaging, the prevalence of them on MRI remains largely unexplored. This study aims to assess the prevalence, age-dependence, anatomical distribution, and content of mylohoid boutonnières as visualized on MRI.Materials And Methods A retrospective review of MRI scans of the head and neck from 294 patients between 2016 and 2020 was conducted. MR images were analyzed for the presence, location, and contents of mylohyoid boutonnières. Inter-rater agreement from the three independent readers with different levels of experience and statistical analysis were performed to assess consistency across readers.Results Mylohyoid boutonnières were identified in 50.7% of individuals, with bilateral deficiencies occurring in 45.6% of cases. Most defects were located in the anterior (45.6%) and middle (51.0%) thirds of the mylohyoid muscle. The herniated content consisted predominantly of salivary tissue (69.3%), followed by fat (15.9%), and blood vessels (14.2%). No significant association was found between mylohyoid boutonnière prevalence and age. There was a high level of inter-rater agreement among all three raters regarding the presence, side, location, and content of the mylohyoid boutonnière, with no statistically significant discrepancies observed across the assessed parameters.Conclusions A mylohyoid boutonnière is a true and common anatomical variant, with a prevalence of 50.7% in this study, and most defects are bilateral. MRI provides high soft tissue contrast, which is beneficial for evaluating oral cavity anatomy, while CT may have higher sensitivity for small bony or soft tissue defects due to its superior spatial resolution. This knowledge aids in preventing diagnostic errors when evaluating oral cavity lesions, minimizing the need for unnecessary invasive procedures.Abbreviations ICC＝ Intraclass Correlation Coefficient; MHB＝ MyloHyoid Boutonnière; MM = Mylohyoid Muscle.