Cross-over accessory anterior belly of the digastric muscle: a rare anatomical variant with embryological background

Résumé fourni par la source

BACKGROUND: The digastric muscle is a key component of the suprahyoid musculature and the floor of the oral cavity. Variants of its anterior belly are reported in up to 10% of cadaveric studies and may present as accessory slips or additional bellies. Such variants are clinically relevant because they may alter surgical anatomy and mimic pathological masses on radiological imaging. Accurate recognition of these configurations is essential for correct diagnosis and safe surgical planning. The aim of this study was to present a rare, isolated unilateral cross-over variant of the anterior belly of the digastric muscle without additional accessory slips, to discuss its embryological background and clinical significance, and to contextualize the finding within published literature and comparative mammalian anatomy. MATERIALS AND METHODS: The variant was identified during routine cadaveric dissection of an 88-year-old male. Detailed anatomical dissection and photographic documentation were performed, with particular attention to muscle attachments and topographical relationships within the submental and submandibular regions. RESULTS: An isolated accessory cross-over anterior belly of the digastric muscle was observed, coursing obliquely from the right intermediate tendon to the left digastric fossa, superficial to the mylohyoid muscle. No additional accessory muscle slips were present. The remaining anterior and posterior bellies demonstrated typical morphology. The variant resulted in marked asymmetry of the floor of the mouth without other associated craniofacial anomalies. This configuration likely reflects a disturbance in migration or condensation of myogenic precursors derived from the first pharyngeal arch during early craniofacial development. Comparative anatomical data indicate that the classical two-bellied digastric muscle with an intermediate tendon is characteristic mainly of humans and certain primates, underscoring the evolutionary specificity of this anatomy. CONCLUSIONS: The presented case highlights a rare, isolated unilateral cross-over configuration of the anterior belly of the digastric muscle. Recognition of such variants is essential in radiological interpretation and in surgical proceduresinvolving the floor of the mouth and upper neck to prevent misdiagnosis and intraoperative complications.

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