Salient Points

• The frontal trigger site includes the supraorbital and supratrochlear nerves (STN). Both nerves are derived from the frontal nerve, which is the largest branch of the ophthalmic division of the trigeminal nerve (V1).

• Eighty-three percent of individuals have a notch, 27% have a foramen, and 10% have both.

• The supraorbital notch contains a fascial band 86% of the time.

• When a supraorbital foramen is present, it is located on average 31 mm lateral to the midline,¹ although this location is inconsistent and can be asymmetric even between the two sides of a single individual.

• After passing through the supraorbital notch or foramen, the SON divides into a deep branch and a superficial branch. The deep branch is located approximately 0.56 mm lateral to a vertical line through the medial limbus.

• The deep branch of the supraorbital nerve (SON) is susceptible to compression inferolaterally.

• As they travel cranially, one or both branches of the SON course directly through the corrugator supercilii muscle (CSM) in 78% of individuals.

• Supraorbital artery travels medial to the SON.

• The STN usually divides into two branches in the retro-orbicularis fat.

• Similar to the SON, one or both branches of the STN may travel through the CSM, which comprises a potential compression or trigger point of the supratrochlear.

• In 84% of individuals, both branches of the STN enter the CSM 18.8 mm lateral to the midline, and exit it 19.6 mm lateral to the midline and 15 mm cranial to the superior orbital rim.²

• The occipital trigger site comprises three sets of nerves, constituting three distinct trigger sites, one medially along the posterior midline (the third occipital), one about 1.5 cm lateral to the midline (greater occipital), and one laterally close to the hairline (the lesser occipital).

• The greater occipital artery can be compressed or irritated at six sites.

• The greater occipital nerve (GON) travels around the lower border of the obliquus capitis inferior muscle, where fascial bands between this muscle and the nerve constitute the first potential compression point of the GON.

• The entrance of the GON into the deep aspect (undersurface) of the semispinalis capitis muscle constitutes the second potential compression point, located 17.5 mm lateral and 59.7 mm caudal to the occipital protuberance.

• The emergence of the GON from the superficial aspect of the semispinalis capitis muscle constitutes the third potential compression point, located 15.5 mm lateral and 34.5 mm caudal to the external occipital protuberance (EOP).

• The GON then continues cranially deep to the trapezius muscle, before entering the deep surface, the fourth potential compression point.³

• The GON then emerges from the tendinous insertion of the trapezius into the nuchal line, at a point 37.1 mm lateral and 4.4 mm caudal to the EOP, and this constitutes the fifth potential compression point.³

• The GON intersects with the occipital artery in 54 to 64% of individuals,4,5 and this intersection constitutes the sixth potential compression point.

• The lesser occipital nerve emerges around the posterior border of the sternocleidomastoid muscle in 86.7% of individuals,⁶ or through the muscle in the remaining 13.3% of individuals, and this constitutes the first potential compression point.

• The lesser occipital compression point is located 61.3 to 68.9 mm lateral to the midline, and 53.2 mm below the level of the external auditory canals.

• The lesser occipital nerve intersects with the occipital artery in 55% of individuals,⁷ and this constitutes the second potential compression point, located 51 mm lateral to the midline and 20 mm caudal to the level of the external auditory canal.