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Superior belly of omohyoid muscle

The superior belly of the omohyoid muscle is a slender, strap-like muscle located in the anterior triangle of the neck. As part of the infrahyoid muscle group, it plays a vital role in depressing the hyoid bone and is easily identified on imaging studies due to its unique anatomical course. Understanding the anatomy, nerve and blood supply, as well as its imaging characteristics, is crucial for clinicians, radiologists, and surgeons involved in head and neck assessments.

Anatomical Description

  • The omohyoid muscle is divided into two bellies: superior and inferior, connected by an intermediate tendon.

  • The superior belly is the vertical segment that extends from the intermediate tendon to the hyoid bone.

  • Lies superficial to the carotid sheath and deep to the sternocleidomastoid muscle in the lateral neck.

Origin

  • The superior belly originates from the intermediate tendon of the omohyoid muscle.

Insertion

  • Inserts onto the lower border of the body of the hyoid bone, just lateral to the insertion of the sternohyoid muscle.

Function

  • Depresses the hyoid bone after it has been elevated during swallowing and speaking.

  • Assists in stabilizing the hyoid bone, aiding in proper tongue movements and swallowing mechanisms.

Nerve Supply

  • Supplied by a branch of the ansa cervicalis (C1-C3 fibers), part of the cervical plexus.

Artery Supply

  • Receives blood from branches of the superior thyroid artery (a branch of the external carotid artery).

Vein Supply

  • Venous drainage is primarily via the superior thyroid vein, which drains into the internal jugular vein.

MRI Appearance

  • T1-weighted: Appears as an isointense structure relative to other skeletal muscles, with clear demarcation from surrounding fat (which is hyperintense).

  • T2-weighted: Shows slightly increased signal intensity compared to T1, muscle fibers are distinguishable but not as bright as surrounding vessels or fat.

  • STIR (Short Tau Inversion Recovery): Demonstrates low signal intensity; fat suppression enhances the contrast between the muscle and surrounding adipose tissue, making muscle pathology (like edema or inflammation) more conspicuous.

CT Appearance

  • Appears as a soft tissue density lateral to the thyroid cartilage and anterior to the carotid sheath.

  • Readily differentiated from surrounding fat due to its higher attenuation; muscle margins are typically well-defined on contrast-enhanced scans.

MRI images

Superior belly of omohyoid muscle mri axial image