INTRODUCTION

Headache is one of the most prevalent, disabling and undertreated conditions in neurological clinical practice.¹ Headache practitioners commonly administer peripheral nerve blocks to treat various headache disorders both in the acute and outpatient setting, often with rewarding results.² There is no current national consensus on the technical aspects of delivering peripheral nerve blocks. However, a recent survey among UK headache practitioners showed that blocks have become relatively popular transitional treatments for cluster headache and chronic migraine.³ Here we aim to provide practical instructions for effective and safe delivery of the most common peripheral nerve blocks used in headache medicine. We briefly outline the evidence base for common indications and describe the peripheral nerve block method, including injection location, technique, drug constituents and potential pitfalls. This, together with the supplementary illustrative videos, should provide a comprehensive guide on nerve block delivery. This guide should be used to support, but not to replace, the experience obtained from clinical supervision by practised healthcare professionals.

EVIDENCE BASE FOR PERIPHERAL NERVE BLOCKS

Headache practitioners frequently target the greater occipital nerve (GON), but the treatment of both primary and secondary headaches might target other cervical and cranial nerves. Despite headache specialists seeing positive results in clinical practice, there is little high-quality information to support their widespread use.⁴

Several recent randomised controlled trials and cohort studies have studied the efficacy of peripheral nerve blocks, particularly GON blocks. The level of evidence for the effectiveness of peripheral nerve blocks for managing different headache disorders varies depending on the pericranial nerve targeted and the outcome measure used (table 1). GON blocks for the acute and preventative treatment of migraine and cluster headaches reduce headache days and give high levels of patient-reported efficacy.^{5 6} Furthermore, peripheral nerve blocks have been effective in managing acute or prolonged migrainous episodes that commonly present to the emergency department.^{7 8} The rapid onset of pain relief provided by anaesthetic nerve blocks makes them ideal for acute headache presentations, where timely management is essential, reducing the need for opiate-based therapies.

Although it is difficult to predict which patients will benefit significantly from peripheral nerve blocks, headache practitioners have developed a wealth of clinical experience in maximising their efficacy. In the trigeminal autonomic cephalalgias—predominantly unilateral headaches including cluster headache and hemicrania continua—ipsilateral greater and lesser occipital nerve (LON) blocks as first-line treatments may avoid the need for corticosteroids or indometacin. Patients with headache who have reproducible pain with palpation over the pericranial nerve area in the scalp, and those with localised cutaneous allodynia, are also likely to respond to nerve blocks.^{7 18} Peripheral nerve blocks are also demonstrably effective in the older population with headache disorders, whose comorbidities might preclude the use of first-line preventative medications.⁶ There are conflicting results about adding corticosteroid to nerve blocks in people with migraine, but evidence to support its efficacy in cluster headache.^{11 14 19} Greater occipital neuralgia with or without another coexisting headache disorder is not uncommon.²⁰ Giving a GON block to a patient with suspected GON neuralgia can be both diagnostic and therapeutic, usually conferring prolonged relief. The evidence base for using peripheral nerve blocks in other cranial neuralgias, such as auriculotemporal and supraorbital neuralgias, is predominantly anecdotal, from published case series.^{15 16} Pregnant women with troublesome headaches can often be managed throughout pregnancy and the post-partum period with anaesthetic nerve blocks without corticosteroid, reducing the need for medications. The frequency of the nerve blocks can be tailored to the individual’s response duration but is usually 3 months or more. If the benefit lasts less than 2 months, then clinicians might consider other headache medications or interventions.

Some headache practitioners inject only the occipital nerves during the first session, which reduces the number of injections and allows for an assessment of initial response. If the patient reports some benefit but has residual facial pain, then at a subsequent session, the trigeminal nerves can be blocked as well as the occipital nerves. Consensus recommendations by the American Headache Society and the Spanish Headache Study Group have used this evidence base to provide guidance on the administration of peripheral nerve blocks for different headache disorders.^{21 22}

GENERAL CONSIDERATIONS

Knowledge of the anatomical landmarks of the occipital and superficial branches of the trigeminal nerve is important for effective nerve blockade, and to avoid possible complications such as nerve trauma, bleeding or inadvertent arterial injection of anaesthetic drug. People with headache disorders often describe pain over the forehead, behind their eyes, temples, occipital and upper cervical areas. The forehead and upper periocular areas are innervated by peripheral branches of the first division of the trigeminal nerve (V1), mainly the supraorbital and the supratrochlear nerves. The temples are largely innervated by the auriculotemporal nerve branch from the mandibular division of the trigeminal nerve (V3). The upper cervical and occipital region is innervated by C2/C3 posterior cervical branches, mainly the greater, lesser and third occipital nerves.²³

Having identified someone as suitable for a peripheral nerve block, we find it helps to show them an illustration of the peripheral cranial nerve to be injected (figure 1). The written consent should include the known complications of any invasive procedure, such as bleeding or infection at the injection site, and some may find the procedure painful. Peripheral nerve blocks are contraindicated at any previous surgical site, for example, previous burr hole or craniotomy, as there is a risk of anaesthetic infiltration into the central nervous system. Blocks should also be routinely avoided in patients with implants such as nerve stimulators or shunts, although in exceptional circumstances can be used in skilled hands with appropriate consent for risks. Following the informed consent process, patients are asked either to lie in a supine position on the examination bed or to sit on a chair, depending on the superficial nerve being injected. Patients should also be advised to eat and drink before attending for the procedure, to reduce the chances of a syncopal episode. As with any invasive procedure, clinicians should take care to confirm the patient’s details and site to be blocked, while adhering to the local personal protection equipment guidance. Topical anaesthetic cream a few minutes before the procedure can be used to numb the skin around the injection site, especially for the supraorbital, supratrochlear and auriculotemporal nerve injection sites. Most people develop numbness in the distribution of the nerve injected within a few minutes after the procedure, and warning patients of this anticipated effect can alleviate postprocedure anxiety. Furthermore, numbness in the dermatomal distribution of the nerve injected is a sign that the procedure has infiltrated the targeted nerve. The constituents of the nerve block differ with the cranial nerve injected and between headache centres (table 2). Corticosteroids are commonly used only for GON blocks, but some headache centres use them to infiltrate the LON as well. We recommend avoiding corticosteroids for any of the trigeminal nerve blocks, particularly due to unwanted cosmetic side effects such as localised alopecia and lipoatrophy.²⁴ The systemic effects of corticosteroids in peripheral nerve blocks are not negligible and there have been reported cases of iatrogenic Cushing’s syndrome both in the literature and anecdotally among headache centres.²⁵ For this reason, it is important to ask the patient about other corticosteroid medications they might be receiving; patients already taking corticosteroids should not receive a repeat corticosteroid-containing nerve block within 3 months or longer. Peripheral nerve blocks appear generally safe, but there are other contraindications and possible complications to take into account, depending upon which cranial nerve is being blocked (table 3).

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Figure 1

Illustrative drawings of the anatomical course of the peripheral cranial nerves. These are used during the consent process to demonstrate the location of the nerves to be injected. Adapted with permission from Blumenfeld et al.²¹

GON BLOCKS

The GON arises as the medial branch from the dorsal primary ramus of the second cervical nerve. It emerges below the obliquus capitis inferior muscle and passes through the semispinalis muscle, before ascending to innervate the posterior scalp to the vertex.²⁹ The GON can be localised superficially by identifying a point one-third (medially) of the way between the occipital protuberance (inion) and the mastoid process, approximately 2 cm lateral and 1.5–2.0 cm below the inion (figure 2). The occipital artery usually runs lateral to the GON, and this should be considered when injecting the nerve.

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Figure 2

Superficial anatomical landmarks for the main cranial nerve blocks. (A) Superficial points for the greater and lesser occipital nerve blocks. (B) Location of the auriculotemporal nerve block. (C) Superficial points for the supratrochlear and supraorbital nerve blocks.

Injection technique

The patient should be comfortably seated on a chair with the head slightly flexed, and the clinician standing behind. Locate the GON, and if needed use topical anaesthetic cream before the injection. Use a 5 mL syringe with a 25-gauge needle. Gently insert the needle perpendicular to the skin, until meeting firm resistance, indicating the needle tip is at the periosteum. This helps to ensure there is no skull defect that might precipitate intracerebral infiltration of the anaesthetic. Withdraw the needle slightly and aspirate to confirm no arterial drawback. Then, redirect the needle slightly superiorly and gently inject the solution in a fanlike distribution (figure 3). Some practitioners inject the solution with the needle in the same position, which is sufficient if injecting a reasonable volume of anaesthetic. The patient may feel a burning sensation as the anaesthetic is infiltrated, but this should subside in a few minutes once the anaesthetic takes effect. Withdraw the needle and apply pressure to the site with gauze to minimise bleeding (online supplemental file 1). If the patient has had previous vasovagal episodes due to pain or previous injections, we recommend performing the injection with the patient in a lateral decubitus position, which will help avoid a sudden fall in blood pressure and hence a sudden decrease in cerebral perfusion pressure.

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Figure 3

Still images illustrating the injection sites of the peripheral nerve blocks. Videos with commentary for these nerve blocks are available in the online supplemental file. (A) Greater occipital nerve blocks. (B) Lesser occipital nerve block. (C) Supratrochlear nerve block. (D) Supraorbital nerve block. (E) Auriculotemporal nerve block.

Supplemental material

[practneurol-2020-002612supp001.mp4]

LON BLOCKS

The LON arises from the ventral primary rami of the second and third cervical nerves. It passes superiorly along the posterior border of the sternocleidomastoid muscle, dividing into cutaneous branches that innervate the lateral portion of the posterior scalp.²⁹ The LON is localised by identifying a point two-thirds of the way between the inion and the mastoid process (figure 2). It is commonly injected along with the GON.

SUPRATROCHLEAR NERVE BLOCKS

The supratrochlear nerve is one of the terminal cutaneous branches of the frontal nerve, which in turn arises from the ophthalmic division of the trigeminal nerve (V1). The supratrochlear nerve exits the orbital cavity anteriorly and ascends the forehead to innervate the upper eyelid, forehead and anterior scalp.²⁹ It is located superficially at the superomedial aspect of the supraorbital ridge, which is the injection site (figure 2).

SUPRAORBITAL NERVE BLOCKS

The supraorbital nerve is the larger of the terminal cutaneous branches of the frontal nerve and runs through the supraorbital notch to innervate the upper eyelid and conjunctiva. It then ascends the forehead, being closely associated medially with the supraorbital artery. The supraorbital nerve is located just above the supraorbital notch (figure 2).

AURICULOTEMPORAL NERVE BLOCKS

The auriculotemporal nerve arises as a posterior division of the mandibular branch of the trigeminal nerve. It innervates the temples and the temporomandibular joint. Its superficial branches innervate the tragus and the auricle of the ear; its proximal trunk is located superficially just anterior to the tragus (figure 2).²⁹

CASE STUDIES

CONCLUSION

Peripheral nerve blocks are effective in the acute and preventative management of several headache disorders. It is difficult to identify those who will respond best, but the procedures allow an interventional approach for those with troublesome and refractory headache. Neurologists can administer these blocks as a day procedure, in clinic or the emergency department, where quick pain relief can provide a satisfactory outcome.

FURTHER READING

1. Blumenfeld A, Ashkenazi A, Napchan U, et al. Expert consensus recommendations for the performance of peripheral nerve blocks for headaches—a narrative review. Headache J Head Face Pain 2013;53:437–46. doi:10.1111/head.12053.

2. Levin M. Nerve blocks in the treatment of headache. Neurotherapeutics 2010;7:197–203. doi:10.1016/j.nurt.2010.03.001.