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Risorius muscle

The risorius muscle is a slender, superficial muscle of facial expression located in the lateral aspect of the face. It plays an important role in retracting the angle of the mouth, thereby producing expressions such as smiling or grinning. Although its size and presence can vary among individuals, the risorius is significant in aesthetic and reconstructive facial procedures as well as in the assessment of facial nerve integrity.

Anatomy and Function of the Risorius Muscle

  • Function

    • Retracts the angle of the mouth laterally.

    • Contributes to expressions such as smiling, laughing, or grimacing.

    • Assists in conveying emotions through facial movements.

  • Origin

    • Fascia over the parotid gland (parotid fascia).

    • Superficial fascia of the cheek.

  • Insertion

    • Skin at the angle of the mouth (modiolus).

  • Nerve Supply

    • Buccal branch of the facial nerve (Cranial Nerve VII).

  • Artery Supply

    • Facial artery (main supply).

    • Transverse facial artery (secondary supply).

  • Vein Supply

    • Facial vein (primary venous drainage).

    • Accompanying veins with the arteries (transverse facial vein).

Imaging Features of the Risorius Muscle

  • MRI Appearance

    • T1-weighted images: The risorius appears as a thin, linear, low-to-intermediate signal structure in the superficial soft tissue plane of the lateral face.

    • T2-weighted images: Shows slightly higher signal intensity compared to T1, but still remains low compared to surrounding fat.

    • STIR (Short Tau Inversion Recovery): The muscle may appear hyperintense if there is edema, but is usually hypointense to isointense in normal conditions.

  • CT Appearance

    • The risorius appears as a thin, soft tissue density structure superficial to the masseter muscle, running horizontally from the parotid fascia to the angle of the mouth.

    • Best visualized with high-resolution facial bone and soft tissue windows.

MRI images

Risorius muscle mri axial image