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Posterior belly of digastric muscle

The posterior belly of the digastric muscle is an essential suprahyoid muscle located in the neck, playing a crucial role in jaw and hyoid movement. It extends from the mastoid notch of the temporal bone to the intermediate tendon, connecting to the anterior belly. Understanding its anatomy, function, and imaging characteristics is important in clinical practice and radiology.

Synonyms:

  • Digastricus posterior belly

  • Posterior digastric muscle

  • Posterior belly of digastric

Function:

  • Depresses the mandible (opens the mouth)

  • Elevates and stabilizes the hyoid bone during swallowing and speech

  • Assists in the movements required for mastication

Origin:

  • Mastoid notch of the temporal bone (medial surface, just medial to the mastoid process)

Insertion:

  • Intermediate tendon, which passes through a fibrous sling attached to the body of the hyoid bone

Nerve Supply:

  • Facial nerve (Cranial Nerve VII), specifically the digastric branch of the facial nerve

Artery Supply:

  • Occipital artery (branch of the external carotid artery)

  • Posterior auricular artery (minor contribution)

Vein Supply:

  • Corresponding veins drain into the posterior auricular vein and occipital vein, eventually draining into the external jugular vein

MRI Appearance:

  • T1-weighted images: Intermediate to low signal intensity, similar to other skeletal muscles

  • T2-weighted images: Normal muscle demonstrates relatively low signal intensity, but increased signal may indicate edema or pathology.

  • STIR (Short Tau Inversion Recovery): Normally low signal, but may appear hyperintense in cases of edema, inflammation, or injury

CT Appearance:

  • Appears as a soft tissue structure of muscle density (slightly higher attenuation than fat), easily differentiated from adjacent fat and vascular structures

  • Outlined by surrounding fascial planes; best visualized in axial and coronal planes

MRI images

Posterior belly of digastric muscleMRI axial image