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Supratrochlear nerve

The supratrochlear nerve is a terminal sensory branch of the frontal nerve, which itself arises from the ophthalmic division (V1) of the trigeminal nerve (cranial nerve V). It provides cutaneous innervation to the medial upper eyelid, medial forehead, and adjacent scalp.^[1] The name derives from its passage superior to the trochlea of the superior oblique muscle; "trochlea" is Greek for pulley.^[1] It emerges from the orbit to supply sensations of touch, pain, and temperature in these regions, playing a key role in sensory feedback from the paramedian forehead.^[2] Originating within the orbital roof, the nerve courses anteromedially alongside the levator palpebrae superioris muscle before passing superior to the trochlea of the superior oblique muscle tendon.^[1] It then exits the orbit through the supratrochlear notch (or foramen, if ossified) at the superomedial orbital rim, approximately 17 mm from the midline, and ascends superficially deep to the frontalis and corrugator supercilii muscles, where it divides into 2–4 terminal rami that pierce the galea aponeurotica to reach the skin.^[3] The nerve's medial position relative to the supraorbital nerve distinguishes it, with the two often anastomosing in the forehead to form a sensory plexus.^[1] Clinically, the supratrochlear nerve is significant in procedures involving the forehead and orbit, such as nerve blocks for migraine relief—where entrapment at the trochlea can contribute to frontal headaches—or in reconstructive surgery like paramedian forehead flaps, where preservation is essential to avoid sensory deficits.^[1] It also carries risks in aesthetic interventions, as inadvertent intra-arterial injection of fillers into its accompanying supratrochlear artery can lead to retrograde embolism and vision loss via the ophthalmic arterial system.^[1] Embryologically derived from neural crest cells, the nerve develops alongside the trochlea by the 12th week of gestation, with its blood supply stemming from the supratrochlear artery, a terminal branch of the ophthalmic artery that anastomoses with supraorbital and superficial temporal vessels.^[1]

Introduction

Definition and etymology

The supratrochlear nerve is the smaller, medial terminal branch of the frontal nerve, which arises from the ophthalmic division (V1) of the trigeminal nerve (cranial nerve V). It serves as a purely sensory nerve contributing to the innervation of the frontal region.^[1]^[3] The term "supratrochlear" originates from the Latin prefix supra-, meaning "above" or "over," combined with "trochlear," derived from the Greek word trochlea (τρόχιλια), signifying a pulley. This nomenclature reflects the nerve's anatomical position superior to the trochlea, the cartilaginous pulley through which the tendon of the superior oblique muscle passes in the medial orbit.^[1]

Overview of location and function

The supratrochlear nerve is a terminal branch of the frontal nerve, which itself arises from the ophthalmic division of the trigeminal nerve (CN V1).^[1] It originates within the roof of the orbit, where it provides initial sensory contributions before emerging to innervate superficial structures.^[2] In terms of its general location, the supratrochlear nerve arises within the orbit and travels anteromedially, passing above the trochlea of the superior oblique muscle. It emerges medially above the superior orbital rim near the midline through the frontal notch, then ascends over the forehead toward the scalp, running parallel but medial to the supraorbital nerve. This positioning situates it along the medial aspect of the upper face, deep to the frontalis and corrugator supercilii muscles as it extends superiorly.^[1]^[2]^[4] As a purely sensory nerve, the supratrochlear nerve conveys cutaneous sensation, including touch, pain, and temperature, to the skin of the medial upper eyelid, the bridge of the nose, the anteromedial forehead, and the adjacent scalp up to the vertex. It also provides mucosal sensation to the conjunctiva and contributes to the somatosensory system for these regions, without any motor or autonomic components. This innervation ensures sensory feedback from the medial forehead and upper eyelid structures, integrating them into the broader facial somatosensory network.^[1]^[2]^[4]

Detailed anatomy

Origin

The supratrochlear nerve originates as the medial and smaller terminal branch of the frontal nerve, which is the largest division of the ophthalmic nerve (CN V1), the first branch of the trigeminal nerve (CN V).^[1] The ophthalmic nerve emerges from the trigeminal ganglion within the cavernous sinus and enters the orbit through the superior orbital fissure, carrying purely sensory fibers without motor contributions.^[1] Within the orbit, the frontal nerve courses anteriorly along the superior aspect, typically dividing into the supratrochlear and supraorbital nerves approximately midway along its intraorbital path, at a distance of about 2-3 cm from the superior orbital fissure. This division marks the initial formation of the supratrochlear nerve, which is consistently smaller than the lateral supraorbital branch.^[1] Embryologically, the supratrochlear nerve develops as part of the sensory component of the ophthalmic division from the trigeminal placode, an ectodermal thickening that contributes neurons to the trigeminal ganglion's ophthalmic lobe, aligned with the first pharyngeal arch derivatives and devoid of motor elements.^[5]

Course and relations

The supratrochlear nerve originates as the medial terminal branch of the frontal nerve within the orbit and courses anteriorly along the superomedial orbital roof, passing superficial to the levator palpebrae superioris muscle and medial to the superior rectus muscle. It continues medially above the trochlea of the superior oblique muscle, maintaining a position superior to the superior oblique tendon while traveling in the extraconal space.^[1]^[2] Upon reaching the anterior orbit, the nerve pierces the orbital septum approximately 17 mm lateral to the midline, emerging just above the medial aspect of the supraorbital margin, often in close proximity to the origin of the frontalis muscle. Initially, it lies deep to the orbicularis oculi muscle and is positioned medial to the trochlea, lateral to the supraorbital nerve, and accompanies the supratrochlear artery—a terminal branch of the ophthalmic artery—that parallels its path after crossing the trochlea.^[1]^[6]^[3] Following emergence, the nerve ascends subcutaneously in the forehead, positioned between the orbicularis oculi and frontalis muscles, facilitating its progression toward the glabellar region.^[1]

Branches and distribution

The supratrochlear nerve emerges from the orbit medial to the trochlear pulley and promptly divides to distribute sensory innervation across the medial periorbital and forehead regions. It gives off medial palpebral branches that supply the skin and conjunctiva of the medial upper eyelid, extending to the superior fornix.^[7]^[8]^[3] A superficial branch arises to innervate the skin of the lower medial forehead and glabella.^[2]^[9] The deeper frontal branch ascends between the corrugator supercilii and orbicularis oculi muscles, pierces the frontalis muscle approximately 15-20 mm superior to the orbital rim, and supplies the upper forehead, root of the nose, and anterior scalp extending as far as the vertex.^[2]^[7]^[10] Overall, the supratrochlear nerve provides sensory innervation to the skin from the medial canthus laterally to approximately 1-2 cm, encompassing the medial half of the upper eyelid, as well as the paramedian forehead.^[8]^[3] It conveys sensations of fine touch, pain, and temperature from these areas via its trigeminal (ophthalmic division) origin.^[1]^[9] The nerve possesses no motor branches, functioning solely as a sensory conduit.^[1]^[2] Its distribution overlaps slightly with the lateral territory of the supraorbital nerve but exclusively covers the paramedian forehead without significant intrusion into more lateral zones.^[3]^[9]

Anatomical variations

Common variations

The supratrochlear nerve exhibits several common anatomical variations, primarily in its point of division from the frontal nerve, branching pattern, and connections with adjacent nerves. One frequent variation involves the location of division, where the frontal nerve bifurcates into the supratrochlear and supraorbital nerves. In a study of 50 orbits, distal division (Variant I) occurred in the anterior half of the orbital length in 36% of cases, with the supratrochlear nerve emerging at a mean distance of 71.2% from the orbital apex, contrasting with the more proximal division (Variant II) seen in 64% of specimens closer to the orbital apex.^[4] Another common deviation is the presence of multiple rami or branches from the supratrochlear nerve. While typically emerging as a single trunk, it often divides into two branches within the retro-orbicularis oculi fat (ROOF) pad before penetrating the corrugator supercilii muscle; this bifurcation was observed frequently in the 50 hemifaces examined in one cadaveric dissection. Up to three or four branches may occur, though less frequently, altering the nerve's intraorbital course through the orbital roof.^[10] Accessory anastomoses between the supratrochlear and supraorbital nerves also represent a typical variation, featuring small connecting twigs that modify the boundaries of their sensory distributions. Additionally, an accessory supratrochlear nerve arising separately was identified in 4% of orbits, often as a thin branch contributing to medial forehead supply.^[4] Rarely, the supratrochlear nerve may be absent or hypoplastic, with complete absence reported in isolated cases but not observed in larger cadaveric series; hypoplasia, characterized by a notably thin nerve, occurred in approximately 11% of 50 orbits studied (30% of cases with distal division). In such instances, sensory compensation often arises from expansion of the supraorbital nerve's territory.^[4]^[1]

Prevalence and detection

Anatomical variations of the supratrochlear nerve, such as accessory branches or atypical intraorbital branching, occur in approximately 25-30% of individuals based on cadaveric dissections and reviews.^[4] A detailed 2019 cadaveric study of 50 orbits reported an accessory supratrochlear nerve in 4% of cases, while intraorbital branching variations were universal, with distal branching (variant I) in 36% and proximal branching (variant II) in 64%; in variant II, 75% of nerves further divided into medial and lateral branches within the orbit.^[4] Clinical observations from over 4,000 headache surgery cases indicate multiple supratrochlear nerve branches in about 30% of patients, with foraminal passage variations in roughly 3%.^[11] These findings underscore the nerve's variability, though prevalence may differ by population, with some evidence of higher rates of multiple branches in Asian cohorts from related trigeminal branch studies.^[12] Detection of supratrochlear nerve variations relies primarily on cadaveric dissection for anatomical research, enabling precise mapping of branching patterns and emergence sites relative to the supraorbital margin.^[4] In clinical settings, high-resolution computed tomography (CT) and magnetic resonance imaging (MRI) facilitate preoperative visualization of emergence points and intraorbital course, with MRI particularly effective for identifying neurovascular relations at the orbital rim.^[13] Ultrasound provides real-time, non-invasive nerve mapping, especially useful for detecting positional variations during guided procedures like nerve blocks, achieving high accuracy in delineating the nerve's superficial trajectory. Post-2020 advancements include increased use of endoscopic intraoperative views in migraine decompression surgeries to identify variations such as deep or multiple branches, enhancing surgical precision.^[11] Emerging 3D imaging models, derived from CT datasets, aid in predicting individual variation patterns for procedural planning, though application remains more established for adjacent supraorbital structures.^[14]

Clinical significance

Nerve blocks for anesthesia and pain relief

The supratrochlear nerve block is indicated for providing regional anesthesia to the medial forehead and upper eyelid, particularly in oculoplastic and plastic surgeries such as laceration repairs or upper eyelid procedures, where precise anatomical approximation is essential without tissue distortion from infiltration. It is also used for acute pain relief in conditions including trigeminal neuralgia, frontal migraines, and cluster headaches, often as part of peripheral nerve blockade targeting the first division of the trigeminal nerve. This block is frequently combined with the supraorbital nerve block to achieve comprehensive coverage of the ipsilateral forehead and periocular region.^[15]^[16]^[17] The procedure employs a landmark-based approach, with the injection site located approximately 1 cm superonasal to the medial canthus, corresponding to the nerve's emergence point medial to the supraorbital notch. A 25- to 30-gauge needle is advanced subcutaneously at a 30- to 45-degree cephalad angle for 0.5 to 1 cm, followed by aspiration to confirm lack of intravascular placement; 1 to 2 mL of 1% to 2% lidocaine, with or without a corticosteroid like triamcinolone for prolonged effect, is then injected to form a subcutaneous wheal around the nerve. Ultrasound guidance enhances precision by visualizing the orbital rim and nerve with a high-frequency linear transducer placed transversely, reducing risks such as globe perforation or intravascular injection, especially in complex cases.^[15]^[16] Clinical evidence supports 70% to 90% efficacy for short-term pain relief in migraine and trigeminal neuralgia, with anesthesia duration typically lasting 4 to 12 hours using lidocaine alone, extending to weeks when steroids are added for chronic conditions. A 2023 review of facial nerve blocks reported high success rates in achieving anesthesia and postoperative analgesia, while case series indicate rapid relief in acute headache attacks, with patient-reported improvements in headache intensity and frequency. Complications are rare but include hematoma, infection, or transient paresthesia, underscoring the block's favorable risk profile for outpatient use.^[15]^[17]^[18]

Surgical decompression for migraines

The supratrochlear nerve is implicated in the pathophysiology of certain chronic migraines through peripheral entrapment, primarily by the corrugator supercilii muscle and, less commonly, the procerus muscle, leading to nociceptor sensitization and activation of central pain pathways.^[19] This compressive mechanism contributes to frontal migraine triggers in a significant subset of patients undergoing surgical evaluation, with frontal sites (involving the supratrochlear and supraorbital nerves) identified in approximately 57% of cases.^[20] Anatomical variations, such as the nerve's emergence point relative to the muscle, may influence the degree of entrapment and surgical planning.^[21] Surgical decompression targets this entrapment via minimally invasive techniques, typically performed endoscopically or through an open approach with a small incision (1-2 cm) in the supraorbital region. The procedure involves selective myectomy of the corrugator supercilii and procerus muscle fibers to release the supratrochlear nerve, often combined with decompression of the adjacent supraorbital nerve; neurectomy is reserved for refractory cases. It is conducted under local anesthesia with sedation or general anesthesia, with operative times averaging 30-60 minutes per site.^[22]^[23] Postoperative outcomes demonstrate substantial efficacy, with systematic reviews reporting a 60-80% reduction in migraine frequency (from a mean of 15-20 headache days per month preoperatively) and severity, sustained over 1-5 years in long-term follow-ups.^[20]^[24] Complete elimination of symptoms occurs in 50-70% of patients, particularly those with confirmed peripheral triggers. Complications are infrequent and mostly transient, including hematoma in fewer than 5% of cases and temporary paresthesia or numbness resolving within 3-6 months; serious adverse events like infection or permanent nerve injury are rare (<1%).^[25]^[26]

Other clinical applications

The supratrochlear nerve is susceptible to injury in cases of frontal sinus fractures or soft tissue lacerations in the glabellar and forehead regions, often resulting from high-impact trauma such as motor vehicle accidents or assaults.^[27] Symptoms typically include hypoesthesia or paresthesia in the medial forehead and upper eyelid, reflecting the nerve's sensory distribution, with transient effects in most cases but a risk of permanent dysesthesia in approximately 5% of cases.^[27] Management generally involves initial conservative approaches like observation and analgesics for minor neuropraxia, but severe neurotmesis may require microneurosurgical intervention, including direct neurorrhaphy or nerve grafting using autologous sural nerve to restore sensory function, particularly if explored within 3-6 months post-injury.^[28] In diagnostic evaluations, the supratrochlear nerve plays a key role in assessing trigeminal neuropathy affecting the ophthalmic (V1) division, where reduced sensation to light touch or pinprick in the medial forehead indicates involvement.^[29] Clinical testing often includes quantitative sensory evaluation of the V1 territory to differentiate peripheral neuropathy from central lesions.^[29] Imaging with computed tomography (CT) or magnetic resonance imaging (MRI) is essential to identify compressive etiologies, such as frontal sinusitis causing mucosal thickening around the nerve or tumors exhibiting perineural spread along V1 branches.^[30] For instance, MRI with gadolinium enhancement can detect abnormal signal intensity in the supratrochlear nerve due to neoplastic invasion, guiding biopsy or oncologic management.^[31] Emerging applications include botulinum toxin type A (BoNT-A) injections targeting muscles innervated by the supratrochlear nerve, such as the corrugator supercilii, for migraine prophylaxis; recent 2024 studies report a 50% reduction in headache days when administered in the frontal region as part of standardized protocols like PREEMPT.^[32] In cosmetic procedures, awareness of the supratrochlear nerve's superficial course in the glabellar region is critical to avoid iatrogenic injury during dermal filler injections, with recommendations emphasizing superficial placement and ultrasound guidance to prevent direct trauma or secondary compression leading to forehead numbness.^[33] Such precautions have reduced nerve-related complications in filler treatments to less than 1% in high-volume practices.^[34]

References

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Anatomy, Head and Neck, Supratrochlear - StatPearls - NCBI - NIH
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### Summary of Supratrochlear Nerve
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Supratrochlear nerve | Radiology Reference Article | Radiopaedia.org
Jun 26, 2024 · The supratrochlear nerve is the medial and smaller of the two branches of the frontal nerve, a branch of ophthalmic division of the trigeminal nerve.
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Anatomical Variations of the Supraorbital and Supratrochlear Nerves
Jul 13, 2019 · The deep branch runs across the lateral forehead between the galea aponeurotica and the pericranium as the sensory nerve to the frontoparietal ...
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Birth of ophthalmic trigeminal neurons initiates early in the placodal ...
May 10, 2009 · Its sensory neurons have a dual origin from both ectodermal placodes and neural crest. Here, we show that the birth of neurons derived from the
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Regional anesthesia in faciomaxillary and oral surgery - PMC
The supratrochlear nerve is measured 17 mm from the glabellar midline and 1-2 ml of 2% lidocaine 1:100,000 in epinephrine is injected. The supraorbital nerve is ...Anatomy · Sensory Supply Of The Head... · Greater And Lesser Occipital...<|control11|><|separator|>
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Supratrochlear nerve - e-Anatomy - IMAIOS
The supratrochlear nerve (n. supratrochlearis), the smaller of the two, passes above the pulley of the Obliquus superior, and gives off a descending ...
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Nerve Supply of the Eyelids - EyeWiki
The superior division passes into the orbit medial to the optic nerve and inferior to the superior rectus muscle. ... The supratrochlear nerve courses ...
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Superficial nerves of the face and scalp: Anatomy | Kenhub
Mar 9, 2015 · The supratrochlear nerve has a complex course and initially travels between the supraorbital foramen and the pulley of the superior oblique.
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[PDF] Anatomy of the Supratrochlear Nerve - Jeffrey E. Janis, MD, FACS
The frontal nerve passes into the orbit through the superior orbital fissure, and midway through the orbit it divides into the supratroch- lear and supraorbital ...Missing: function | Show results with:function
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Anatomic Anomalies of the Nerves Treated during Headache Surgery
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The supratrochlear nerve block is a special procedure, which can be utilized to relieve pain in the mid-forehead region.
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We provide instructions and an audiovisual guide for administering greater and lesser occipital, supratrochlear, supraorbital and auriculotemporal nerves blocks ...<|control11|><|separator|>
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In patients with chronic migraine, the CSM is targeted for BoNT injection because it is related to the entrapment of the supratrochlear nerve within the CSM.<|control11|><|separator|>
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Conclusion: Migraine surgery provided a clinically and statistically significant reduction in headache frequency, severity, and migraine headache index scores.
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Jul 17, 2015 · The supratrochlear nerve (STN) and supraorbital nerve (SON) constitute the terminal branch of the frontal nerve, which is a major branch of the ...
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Feb 19, 2019 · Paresthesias in the supratrochlear and supraorbital distributions are usually transient but have a long-term incidence of permanent dysesthesia ...Diagnosis · Treatment · Complications
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This chapter reviews the relevant surgical anatomy, clinical indications, and timing for surgical repair of the inferior alveolar and lingual nerve injuries.1. Introduction · 2. Indication And Timing For... · 3. Principles Of Surgical...Missing: supratrochlear | Show results with:supratrochlear
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The trigeminal nerve (cranial nerve V) has sensory and motor components, controlling facial sensation and masticatory movements. It is a mixed cranial nerve.
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What a Neurologist Should Know about Functional Anatomy for ...
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Dec 12, 2013 · Inadvertent nerve damage is a rare complication of dermal filler procedures and can occur as result of direct trauma where the nerve is ...