Morphological classification of the temporalis muscle: anatomical, radiological, and surgical perspectives

The temporalis muscle (TM) shows substantive morphological variability with direct implications for surgical planning and imaging interpretation. Drawing on cadaveric series and imaging cohorts, we critically synthesise convergent findings on layered architecture, distal tendon configuration and retromolar extensions, and highlight discrepancies largely attributable to plane/sequence selection and operator dependence in magnetic resonance imaging and ultrasound. We propose a four-type classification with operational criteria based on fascicular architecture, terminal tendon pattern and accessory slips, including relationships to the deep temporal fascia and the temporomandibular joint capsule. This scheme should be regarded as a pragmatic, hypothesis-generating framework derived from heterogeneous descriptive datasets rather than a statistically validated taxonomy. Where available, we summarised reported frequencies of Types II-IV across cadaveric and imaging cohorts using a study-level evidence map. We further translate type-specific anatomy into decision support for flap harvest and lengthening temporalis myoplasty, osteotomy/coronoidectomy planning, targeted management of temporomandibular disorders (e.g., botulinum toxin, dry needling), and radiotherapy contouring. Recognising temporalis variability can improve diagnostic accuracy, optimise operative strategy and reduce complications, while underscoring the need for harmonised definitions and prospective validation.