Supraorbital and supratrochlear block: anatomy and risks

The forehead and anterior scalp receive sensation from two small nerves, the supraorbital and the supratrochlear. They are the target of a block in specific contexts, but they run beside arteries that are part of one of the most critical regions of the face. This page covers anatomy, indication and risks at a review level, without describing the technique step by step. Preparation, dose, route and authorization follow the anesthetic's package insert, the training and the rules of each professional's council in Brazil.

What anatomy is involved?

The supraorbital and supratrochlear nerves are branches of the ophthalmic nerve (V1), which comes from the trigeminal. The supraorbital nerve emerges from the orbit through a notch or a supraorbital foramen, at the upper margin of the orbit, and climbs up the forehead. The supratrochlear nerve exits more medially, near the root of the nose, and also heads to the forehead. Both supply the skin of the forehead, part of the upper eyelid and the anterior scalp.

Each nerve is accompanied by an artery of the same name, the supraorbital and the supratrochlear, branches of the ophthalmic artery. This is what makes the area dangerous: the arteries connect with the circulation of the eye region. The exact position of the foramen or notch varies, and must be examined in each patient.

When is the block considered?

It is rare in routine HOF. It may be considered in painful procedures of the forehead or anterior scalp, in patients with low pain tolerance. For most botulinum toxin and filler injections, comfort is achieved with simpler strategies: topical anesthetic, ice, vibration and distraction. The overview of options is in local anesthesia in HOF: overview and in topical anesthetics: composition and risks.

Many professionals conclude that, for toxin in the forehead, the risk of the block does not outweigh the benefit. The decision is individual and documented.

What are the risks?

• Intravascular injection, with the potential for a vascular event and, rarely, visual consequences. See visual complication after filler and glabellar vascular occlusion.
• Bruising, because of the vascularity of the area.
• Nerve injury, with transient paresthesia. See paresthesia after an HOF procedure.
• Systemic toxicity if there is rapid absorption or an inadequate dose. See systemic toxicity from local anesthetic.
• Eyelid swelling and apparent drooping of the eyelid from numbness and swelling, which can be mistaken for ptosis of another cause. See eyelid ptosis vs brow ptosis.
• Pallor from the vasoconstrictor, which can be mistaken for ischemia. See vascular occlusion vs anesthesia pallor.

Safety principles, without technique

1. Decide whether you need it. If a less invasive alternative solves it, that is usually the best choice.
2. Medical history: allergies, anticoagulants, heart disease, pregnancy, medications. See medical history in HOF.
3. Dose according to the package insert and weight, with a record. See heart disease and anesthetics with vasoconstrictor when there is heart disease.
4. Emergency preparation: kit and protocol rehearsed. See HOF office emergency kit.
5. Training: add the technique to your routine only with supervised hands-on training.
6. Specific informed consent, with the vascular risks described.

What the patient feels and needs to know

After a forehead block, the patient may notice numbness of the forehead and anterior scalp, a feeling of heaviness in the upper eyelid and, in some cases, an apparent transient eyelid droop from swelling. This is frightening, and explaining it beforehand reduces anxiety. Explain that sensation returns gradually, that they should not scratch or press the area unnecessarily and that any visual change, increasing pain or color change must be reported immediately.

It is also important to agree on post-procedure contact: a direct phone number, a follow-up time and the instruction to seek emergency care if they cannot reach the professional. This organization is worth more than any technical detail, because the outcome of a vascular complication depends on time. See post-procedure instructions and when to call SAMU (Brazil's mobile emergency service).

Anatomical variations that change management

The supraorbital foramen can be an open notch or a complete hole, it can be more medial or more lateral, and in some patients there are accessory branches. The supratrochlear nerve is usually thinner and more variable. These variations mean that palpation and examination of each patient matter, and that no standard measurement works for everyone. The same applies to the arteries that accompany the nerves, whose caliber and course also vary. The practical rule is to assume the vessel is where you least expect it, and to plan caution from there. See vascular anatomical variations and periorbital anatomy for injectables.

Regulation and responsibility

Permission to perform regional anesthesia varies with training and with the rules of each professional's council, and those rules change. Check the regulation that applies to your council before adding any block and record the guidance you received. This page does not indicate which professional category may or may not perform the technique. See HOF regulation at the CFO, facial harmonization and the CFM and facial harmonization in biomedicine and the CFBM.

The block and the assessment of the forehead

In botulinum toxin treatment, assessing the dynamics of the forehead and glabella, with the patient frowning and raising the eyebrows, guides management. If the forehead is anesthetized before that assessment, the perception of movement and symmetry may be impaired by swelling. So the practical rule is to assess, photograph and only then, if appropriate, anesthetize. See muscle map for botulinum toxin and botulinum toxin in the frontalis muscle.

Where does Harmy come in?