Oral Cavity Lesion Mimicker: How Prevalent Is the Mylohyoid Boutonnière on MRI?

The mylohyoid muscle is commonly considered a continuous muscular sling, but it is frequently discontinuous, forming mylohyoid boutonnières (MHBs) that can contain salivary tissue, fat, blood vessels, or lymph nodes. While some studies have explored MHBs in cadavers and through CT imaging, the prevalence of them on MRI remains largely unexplored. This study aims to assess the prevalence, age dependence, anatomic distribution, and content of MHBs as visualized on MRI.

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 MHBs. Interrater agreement from the 3 independent readers with different levels of experience and statistical analysis were performed to assess consistency across readers.

MHBs 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%) one-third 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 MHB prevalence and age. There was a high level of interrater agreement among all 3 raters regarding the presence, side, location, and content of the MHB, with no statistically significant discrepancies observed across the assessed parameters.

An MHB is a true and common anatomic 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.