Where is the Supraorbital Notch Located?
The supraorbital notch is located on the external surface of the cranium (facies externa). It forms part of the supraorbital margin (margo supraorbitalis), which marks the superior boundary of the orbital opening (aditus orbitalis).
The notch is situated within the medial half of the supraorbital margin. Anatomical variations are common: the margin may feature an open supraorbital notch (incisura supraorbitalis) or a closed supraorbital foramen (foramen supraorbitale). Medial to it, closer to the glabella, the frontal notch or foramen (incisura/foramen frontale) may also be present.
What Passes Through the Supraorbital Notch?
The supraorbital margin connects the orbit to the facial region. The neurovascular structures passing through or near the supraorbital notch include:
- Frontal nerve (n. frontalis) — a branch of the ophthalmic nerve (n. ophthalmicus), which is the first division of the trigeminal nerve (CN V).
- Supraorbital artery (a. supraorbitalis) — a branch of the ophthalmic artery (a. ophthalmica). It passes through the incisura supraorbitalis to supply the forehead, the frontal belly of the m. occipitofrontalis, and the skin of the forehead, forming anastomoses with the superficial temporal artery (a. temporalis superficialis).
- Supraorbital vein (v. supraorbitalis).
Sensory Pathway
The fibers traveling through the supraorbital notch are peripheral processes of primary sensory neurons—pseudounipolar cells located in the trigeminal ganglion (ganglion trigeminale). These neurons synapse with peripheral receptors responsive to pain, temperature, pressure, and touch.
The central processes enter the tegmentum of the pons and terminate in the sensory nuclei of the trigeminal nerve:
- Nucleus tractus spinalis n. trigemini — processes pain and temperature modalities.
- Nucleus sensorius superior n. trigemini — processes tactile sensation.
Axons of secondary neurons decussate and ascend to the ventral posterolateral (VPL) or ventral posteromedial (VPM) nuclei of the thalamus. Tertiary neurons project from the thalamus to the lower part of the postcentral gyrus (primary somatosensory cortex).
Clinical Significance
- Assessment of motor response: Pressure applied to the supraorbital notch is a standard noxious stimulus used in coma scales. Localization of the pain by the patient (e.g., bringing a hand above the clavicle) corresponds to a specific score in motor response evaluations.
- Collateral circulation assessment: The ophthalmic artery branches are clinically important for evaluating collateral blood flow between the internal and external carotid artery systems.