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Masseter muscle

The Masseter muscle is a thick, rectangular muscle located in the jaw region, primarily responsible for elevating the mandible (jawbone) to facilitate chewing (mastication). As one of the four muscles of mastication, the Masseter is powerful and easily palpable, extending from the zygomatic arch (cheekbone) to the lateral surface of the mandibular ramus. This muscle plays a crucial role in jaw closure and is often examined in clinical settings for disorders such as bruxism, temporomandibular joint dysfunction, and other myofascial pain syndromes.

Synonyms and Related Terms

  • Masseteric muscle

  • Jaw muscle

  • Masticatory muscle (as a group)

  • Musculus masseter (Latin)

  • External masticatory muscle

Anatomical Details

  • Location: Lateral aspect of the mandibular ramus

  • Origin: Zygomatic arch (inferior border and medial surface)

  • Insertion: Lateral surface of the mandibular angle and ramus

  • Function: Elevation and minor protrusion of the mandible

MRI Appearance of the Masseter Muscle

Proton Density (PD) Sequence

  • The Masseter muscle displays intermediate signal intensity on PD sequences.

  • Normal muscle architecture may be visualized as relatively uniform in signal with possible subtle striations.

  • Surrounding fascia appears as a low signal line demarcating the muscle borders.

STIR (Short Tau Inversion Recovery) Sequence

  • On STIR images, the Masseter muscle appears uniformly hypointense (dark) relative to subcutaneous fat.

  • This sequence is sensitive for detecting edema or inflammation, which would appear as high signal (bright) areas within the muscle in pathologic states.

  • Normal Masseter muscle should not exhibit areas of abnormal high signal intensity.

T1-Weighted Sequence

  • On T1-weighted images, the Masseter muscle demonstrates low to intermediate signal intensity, darker than fat and similar to other skeletal muscles.

  • Muscle boundaries are sharply delineated, and the muscle appears homogenous in healthy individuals.

  • Pathological changes (e.g., atrophy, fatty infiltration) may alter the signal characteristics, but normal Masseter muscle remains relatively uniform on T1

MRI images

Masseter muscle

CT image

Masseter muscle CT axial image-img-00000-00000