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Lateral rectus muscle

The lateral rectus muscle is one of the six extraocular muscles responsible for the coordinated movement of the eyeball. Located in the orbit, this muscle is primarily involved in the abduction of the eye, allowing the eyeball to move laterally (away from the midline). It plays a crucial role in binocular vision, enabling the eyes to align properly for clear and single vision.

Synonyms:

  • External rectus muscle

  • Lateral rectus oculi muscle

  • Rectus lateralis

Function:

  • Primary action: Abduction of the eyeball (moves the eye laterally, away from the nose)

  • Innervated by the abducens nerve (cranial nerve VI)

  • Essential for lateral gaze and coordinated horizontal eye movements

  • Works in conjunction with the medial rectus muscle of the opposite eye during conjugate gaze

MRI Appearance:

  • T1-weighted images:

    • Muscle appears isointense to other extraocular muscles

    • Homogeneous, intermediate signal intensity

    • Fat surrounding the muscle appears hyperintense

  • T2-weighted images:

    • The muscle is usually isointense to slightly hypointense compared to orbital fat

    • Edema, inflammation, or pathology may cause hyperintensity

  • STIR (Short Tau Inversion Recovery):

    • Normal muscle appears β€‹slightly hyperintense (mildly bright) compared to T2 and T1 due to fat suppression.

    • Pathological changes such as edema or myositis show as increased signal (hyperintense)

    • Surrounding orbital fat is suppressed and appears dark

CT Appearance:

  • Non-contrast CT:

    • Appears as a well-defined, elongated soft tissue structure lateral to the globe

    • Similar density to other extraocular muscles

    • Clearly visualized against the low-attenuation background of orbital fat

  • Contrast-enhanced CT:

    • May show mild enhancement, especially if inflamed or involved in a disease process

MRI images

Lateral rectus muscle mri image