Anatomy

The supraorbital nerve (SON) is purely a general sensory (afferent) nerve. The supraorbital nerve is a continuation of the frontal nerve, which is one of the three main branches of the ophthalmic division (V1) of the trigeminal nerve (the fifth cranial nerve) ( Figs. 32-1 and 32-2 ).

Nerve supply for the face ( right ) and the sensory distribution of the trigeminal nerve ( left ).

(Adapted from NYSORA.com .)

Anatomy/branches of the trigeminal nerve.

The supraorbital nerve exits from the supraorbital foramen or notch along the superior rim of the frontal bone, accompanied by the supraorbital artery. In the supraorbital notch, the supraorbital nerve gives off small filaments that supply the mucosal membrane of the frontal sinus and filaments that supply the upper eyelid. The supraorbital nerve is usually located 2.7 cm from the midline ( Fig. 32-3 ).

Anatomy of supraorbital nerve. The diagram illustrates the courses of the deep (SON-D) and the superficial (SON-S) divisions of the supraorbital nerve trunk that form just after the trunk exits the supraorbital rim. The SON-D runs superiorly and obliquely across the forehead between the galea aponeurotica and the periosteum by the mid-forehead level, runs parallel to and between 0.5 and 1.5 cm medial to the superior temporal line (STL) of the skull. This relationship with the STL over the forehead continues onto the scalp area. Just before reaching the level of the coronal suture (CS), the SON-D typically bifurcates before forming the fine terminal branches (TBr) that pierce the galea aponeurotica and enter the frontoparietal scalp. The SON-S division forms branches that pass through the lower frontalis muscle at variable levels to run cephalad over this muscle and enter the anterior scalp.

(Adapted from Knize DM: A study of the supraorbital nerve. Plast Reconstr Surg. 1995;96:564-569.)

The supraorbital nerve course beyond the supraorbital notch has only recently been explored due to advancement in plastic surgical techniques. The detailed anatomic course and its innervations is studied in fresh cadaver specimens and its sensory distribution in living subjects using selective nerve block. SON divides to two branches above the orbital rim, the superficial and deep branches. The medial (superficial) division passes over the frontalis muscle and divides into multiple smaller branches with cephalic distribution toward the hairline. It provides sensory innervations to the forehead skin and anterior scalp as far as the vertex. The deep (lateral) division runs deep in the frontalis across the lateral forehead between the galea aponeurotica and the pericranium. The deep division supplies sensory innervation to underlying periosteum and frontal parietal scalp.

The supratrochlear nerve (STN) is a branch of the frontal nerve and supplies sensory innervations to the bridge of the nose, medial part of the upper eyelid, and medial forehead. The supratrochlear nerve is usually located 1.7 cm from the midline.

Pathophysiology of Supraorbital Neuralgia

The supraorbital nerve can be affected by trauma, inflammatory processes, infection, and tumors. Traumatic injuries to skull or soft tissue at the forehead can cause partial or total nerve injuries. This causes numbness and paresthesias in the forehead and anterior skull area. Neoplastic processes can directly or indirectly compromise the supraorbital nerve along its course.

Trigeminal neuralgia (tic douloureux) mainly affects the second and third divisions of the trigeminal nerve. The first division and its branches, including the supraorbital nerve, are affected in about 5% of patients. In most cases, compression by an overlying vein or artery can cause demyelination of the central nervous system portion of the trigeminal nerve. The other causes are demyelinating processes (such as multiple sclerosis) within either the central or peripheral course of the nerve or in the brainstem.

Postherpetic neuralgia (PHN) is due to reactivation of the varicella-zoster virus in advanced age, immunocompromised patients, and malignancies such as lymphoma. When the trigeminal nerve is involved, the first division is most commonly affected. After chickenpox has resolved, the virus remains latent in the dorsal root ganglia where it can reactivate later in life. Postherpetic neuralgia is characterized by the persistence of neuropathic pain after the rash has resolved. The pathophysiology of postherpetic neuralgia is unclear; there is evidence of neuronal pathology, peripheral and central demyelination.