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Superior rectus muscle

The superior rectus muscle is one of the six extraocular muscles responsible for controlling the movement of the eye. Located in the orbit, this muscle plays a crucial role in elevating the globe and facilitating upward gaze. Its anatomy, function, and radiological appearance are important considerations in ophthalmology, radiology, and neurology.

Synonyms

  • Superior rectus

  • Superior rectus oculi

  • Musculus rectus superior (Latin)

  • SR muscle

Function

  • Primary action: Elevates the eye (moves the globe upward)

  • Secondary actions: Adduction (moves the eye inward), and intorsion (rotates the top of the eye toward the nose)

  • Innervated by the superior division of the oculomotor nerve (cranial nerve III)

  • Essential for coordinated upward gaze and visual tracking

MRI Appearance

  • T1-weighted images:

    • Superior rectus muscle appears as an intermediate to low signal intensity structure compared to orbital fat

    • Clear delineation from surrounding orbital fat due to contrast in signal intensity

  • T2-weighted images:

    • Typically shows a low to intermediate signal intensity

    • Pathological conditions (e.g., inflammation, edema) may cause increased signal intensity

  • STIR (Short Tau Inversion Recovery):

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

    • Hyperintensity may indicate edema or myositis

    • Useful for detecting inflammatory changes or muscle enlargement

CT Appearance

  • Appears as a well-defined, soft tissue density structure in the superior orbit

  • Homogeneous attenuation, similar to other extraocular muscles

  • On contrast-enhanced CT, shows mild enhancement

  • Enlargement, abnormal contour, or loss of definition may indicate pathology (e.g., thyroid ophthalmopathy, myositis, tumor)

MRI images

Superior rectus muscle mri image