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Supratrochlear nerve

The supratrochlear nerve is a small sensory branch of the ophthalmic division (V1) of the trigeminal nerve. It plays a crucial role in providing sensory innervation to the skin and tissues of the medial forehead and upper eyelid. Given its superficial location and clinical significance in both neurological assessment and surgical procedures involving the forehead and orbit, understanding its anatomical course, function, and imaging appearance is important for radiologists, neurologists, and surgeons.

Synonyms

  • Branch of the frontal nerve (as the supratrochlear nerve is a terminal branch of the frontal nerve)

  • Nerve to the medial forehead

  • Medial supraorbital nerve (less commonly used and should not be confused with the supraorbital nerve)

Function

  • Provides sensory innervation to the skin of the medial aspect of the forehead, root of the nose, and upper eyelid (medially).

  • Supplies part of the conjunctiva of the upper eyelid.

  • Plays a role in transmitting tactile, pain, and temperature sensations from the aforementioned regions.

Anatomy

  • Arises from the frontal nerve, which is itself a branch of the ophthalmic division (V1) of the trigeminal nerve.

  • Travels above the trochlea of the superior oblique muscle in the orbit.

  • Passes superiorly and medially, exiting the orbit to ascend in the subcutaneous tissues of the forehead.

  • Often accompanied by the supratrochlear artery.

MRI Appearance

  • T1-Weighted Images:

    • The supratrochlear nerve appears as a small, hypointense (dark) linear structure within the orbit and subcutaneous tissues, best visualized with high-resolution imaging.

    • May not be distinctly visualized in standard head MRI unless using dedicated orbital protocols.

  • T2-Weighted Images:

    • The nerve typically appears hypointense or isointense relative to surrounding fat and soft tissue.

    • Inflammation or injury may cause mild hyperintensity.

  • STIR Sequence:

    • Nerve is normally hypointense, but will appear hyperintense (bright) if there is neuritis, edema, or injury due to the fluid-sensitive nature of STIR.

    • STIR is useful for detecting abnormal signal or nerve pathology.

CT Appearance

  • The supratrochlear nerve itself is not directly visualized on routine CT due to its small size and low contrast with surrounding soft tissues.

  • High-resolution CT may allow indirect identification by recognizing the small foramen or groove at the superior-medial orbital rim through which it exits.

MRI images

Supratrochlear nerve mri image