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Superior oblique muscle

The superior oblique muscle is a slender, fusiform extraocular muscle that plays a crucial role in the movement of the eyeball, especially in downward and outward gaze. It originates from the sphenoid bone, courses anteriorly in the orbit, passes through the trochlea (a fibrocartilaginous pulley), and inserts on the superolateral aspect of the globe. Its unique path and function distinguish it from the other extraocular muscles.

Synonyms:

  • Superior oblique

  • Musculus obliquus superior (Latin)

  • SO muscle

Function:

  • Primary Action: Intorsion (internal rotation) of the eyeball

  • Secondary Action: Depression of the eyeball when in adduction

  • Tertiary Action: Abduction of the eyeball

  • Clinical Relevance: Essential for coordinated eye movement, reading, and maintaining binocular vision. Dysfunction may lead to vertical or torsional diplopia.

MRI Appearance:

  • T1-Weighted Images:

    • The superior oblique muscle appears as a well-defined, intermediate-to-low signal intensity structure within the superior medial orbit.

    • Muscle boundaries are clear, with uniform signal.

  • T2-Weighted Images:

    • The muscle is generally low signal intensity, slightly higher than the adjacent bone but lower than orbital fat.

    • Pathology (edema, inflammation) may appear as increased T2 signal.

  • STIR (Short Tau Inversion Recovery):

    • The posterior band appears slightly hyperintense (mildly bright) compared to T2 and T1 due to fat suppression.

    • Hyperintensity suggests edema, myositis, or acute injury.

    • Useful for detecting subtle inflammation or soft tissue pathology.

CT Appearance:

  • The superior oblique muscle appears as a linear, soft-tissue density structure in the superomedial orbit.

  • Best visualized on coronal and axial sections, medial to the superior rectus and above the medial rectus.

Superior oblique muscle mri image