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Frontal nerve

The frontal nerve is a prominent sensory branch of the ophthalmic division (V1) of the trigeminal nerve. It plays a crucial role in the sensory innervation of the forehead and scalp. Understanding the frontal nerve’s anatomy, function, and imaging characteristics is essential for interpreting cranial nerve pathologies and surgical planning.

Synonyms:

  • Supraorbital nerve (as one of its major branches)

  • Ophthalmic nerve branch (V1 branch)

  • N. frontalis (Latin)

Function:

  • Sensory innervation to the skin of the forehead

  • Sensory supply to the upper eyelid

  • Sensory branches to the mucosa of the frontal sinus

  • Provides sensation to the scalp up to the vertex

Anatomy:

  • Largest branch of the ophthalmic nerve (V1)

  • Divides into two main branches:

    • Supraorbital nerve (lateral)

    • Supratrochlear nerve (medial)

  • Courses anteriorly within the orbit, superior to the levator palpebrae superioris muscle

  • Exits the orbit through the supraorbital notch or foramen

MRI Appearance:

  • T1-weighted images:

    • The frontal nerve appears as a small, low-signal (dark) linear structure within the orbit

    • Surrounded by orbital fat, which is hyperintense (bright)

  • T2-weighted images:

    • The nerve remains low to intermediate signal intensity

    • Orbital fat remains bright, providing good contrast for nerve identification

  • STIR (Short Tau Inversion Recovery):

    • Nerve is low signal (dark),

    • STIR suppresses fat, so the nerve may be harder to distinguish unless inflamed (inflammation will appear hyperintense/bright)

  • Best visualized in dedicated high-resolution MRI orbital sequences

CT Appearance:

  • Not directly visualized due to small size and soft-tissue density

  • Course can be inferred relative to bony landmarks (e.g., supraorbital foramen/notch)

MRI images

Frontal nerve