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Occipital Neuralgia: Advances in the Operative Management
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.315980
Keywords: Decompression surgeries, headache disorders, occipital neuralgia
Headache disorders, in particular migraine headaches and occipital neuralgia, have emerged as a major cause of morbidity worldwide. While there are currently no epidemiological studies documenting the worldwide prevalence or incidence of ON,[1] a small study of the Dutch population reported an estimated incidence of 3.2 cases per 100,000 individuals.[2] Further studies are therefore needed to confirm absolute data. While occipital neuralgia and migraines with predominant occipital pain are thought to be separate and distinct entities, there is often overlap in their presentation and consequently overlap in surgical treatment.[3],[4],[5],[6],[7] The majority of the publications on surgical decompression are on migraines, but most peripheral nerve surgeons understand that occipital neuralgia patients respond just as well if not better to surgery than patients with migraines with predominant occipital pain .[8] Evidence has identified at least four regions as trigger points for migraine headaches with potential surgical interventions. In the frontal and temporal regions, the irritation stems from the supraorbital/supratrochlear nerves, zygomaticotemporal branch of the trigeminal nerves, and auriculotemporal nerve[9] respectively. A third trigger site is related to turbinate and septal pathology.[3] The greater occipital nerve (GON) is involved in migraine of the occipital area, as well as possibly the accompanying lesser occipital nerve (LON).[7],[10] Occipital neuralgia (ON) is a distinct type of headache characterized by paroxysmal pain in the distribution of the greater, lesser, or third occipital nerves,[1] and has been described as a more peripheral irritation of the nerve rather than a central process like migraines. The pain may be caused by nerve injury, irritation, or compression by surrounding structures, such as the semispinalis capitis muscle, fibrous bands, and occipital artery.[3] While some cases are idiopathic, possible causes include trauma, compression (C1-C2-C3 osteoarthritis), or inflammation (rheumatoid polyarthritis or spondyloarthritis).[11],[12],[13] In this article, we shall review the medical and surgical management of ON and describe our approach to the surgical decompression of occipital neuralgia. Medical management Conservative management of ON is directed at alleviating secondary muscle tension and improving posture.[14] Anti-inflammatory medications and prescription muscle relaxants may reduce acute pain.[1] Other first-line drugs include the off-label use of antiepileptic medications, such as gabapentin, pregabalin, and carbamazepine, or antidepressants, such as amitriptyline.[11],[14] While these medications have been reported to reduce the frequency and severity of headaches, none have been systemically evaluated for the treatment of ON.[1],[14] Very little has been published in regards to oral steroids for the treatment of ON. One retrospective study of 43 patients, diagnosed with cluster headaches and not ON found that oral steroids compared to GON injections led to a greater incidence of partial response (82.7% vs 64.4%) and complete response (50.6% vs 35.6%) in patients diagnosed.[15] It is not uncommon for results to be unsatisfactory with medication alone, and patients may try multiple regimens in search of pain relief,[11] eventually requiring more invasive treatments. Anatomical considerations In order to understand the management of ON, the pertinent anatomy must be discussed. The GON originates from the medial branch of the dorsal ramus of the C2 spinal nerve. It emerges under the obliquus capitis inferior muscle and moves cephalically to the suboccipital triangle.[11] It then pierces the semispinalis capitis muscle and runs rostrolateral deep to the trapezius muscle.[1],[16] It pierces the trapezius aponeurosis slightly inferior to the nuchal ridge, where it enters the subcutaneous layer and lies medial to the occipital artery.[3] The GON provides sensory innervation to a large portion of the posterior scalp up to the vertex.[17] The lesser occipital nerve (LON) originates from the lateral branch of C2 and sometimes C3 in the cervical plexus. It travels along the posterior border of the sternocleidomastoid muscle and provides sensation to the inferior occiput.[1] It also innervates the lateral scalp posterior and superior to the ear.[11],[17],[18] Finally, the third occipital nerve is a branch of the posterior ramus of the C2 spinal nerve.[11] It emerges from the semispinalis capitis and trapezius muscles to innervate the upper neck and lower occipital scalp [Figure 1].[1],[17],[19]
Occipital nerve blockade Included in the International Headache Society diagnostic criteria of ON is pain that is temporarily eased by local anesthetic injection to the affected nerve.[20] Besides aiding in diagnosis, the temporary relief provided by these anesthetic blocks or steroid injections makes them a high-yield intervention to alleviate pain associated with ON.[1] The effects of a GON block are thought to be due to diminished afferent input to the second-order trigeminal nucleus caudalis neurons, which receive input from the occipital and trigeminal afferents, leading to decreased central sensitization if there is a migraine component to the headache.[21],[22] Anesthetic blocks can be guided using anatomical landmarks or imaging modalities, such as fluoroscopy and ultrasound.[11] According to an expert consensus published by the American Headache Society, the recommended site of injection for a GON block is one-third of the way from the external occipital protuberance to the mastoid process.[21],[23] The expert consensus also recommended for a LON block, the injection should be two-thirds of the way from the external occipital protuberance to the mastoid.[23] Our experience in peripheral nerve surgery is more concise. The GON is one to two centimeters from the midline and three centimeters inferior to the occipital protuberance and deep to the trapezius fascia. The exact area to block is then guided by the patient's tenderness while sitting in a neck flexed position.[3] The LON emerges from the posterior border of the sternocleidomastoid. The area of tenderness is palpated, with the muscle at an average of six centimeters lateral to the y-axis and seven centimeters caudal to the x-axis. (The y-axis is the vertical midline in the posterior scalp through the midline of the cervical spine. The x-axis is a horizontal line drawn between the most anterosuperior points of the external auditory meatus.) [Figure 1]. The injection in this area is less deep than the GON.[24] The third occipital nerve is not routinely injected, as it is not often involved in headache pathology.[25] The most widely used nerve blocks are lidocaine and bupivacaine, which can be combined in an attempt to achieve a rapid onset of nerve blockade and a longer duration of action due to the presence of bupivacaine.[1],[21] The AHS expert consensus recommends using 1-2% lidocaine and/or 0.25-0.5% bupivacaine.[21] If a combination is used, the recommended volume ratio of lidocaine to bupivacaine is 1:1-1:3.[21] Corticosteroids have frequently been used in combination with anesthetic nerve blocks, most commonly 40 mg triamcinolone or 40-80 mg methylprednisone.[21] There are currently no studies confirming the addition of a corticosteroid increases the efficacy or duration of pain relief in patients with ON.[1] The evidence to support the use of corticosteroids with local anesthetic appears to be strongest for cluster headaches, though further investigation is necessary.[26] While several studies have shown the benefits of anesthetic nerve blockade, effects of these treatments, however, are often short-lived and repeat injections may be required.[11] While Kuhn et al. reported a minimum of 80% pain relief in ten subjects treated with infiltration of the GON with 0.5% bupivacaine followed by a corticosteroid, the benefits lasted from one week to four months.[27] Onabotulinum Toxin Type A The Phase III Research Evaluating Migraine Prophylaxis Therapy (PREEMPT) trial prompted FDA approval of Onabotulinum Toxin Type A for the treatment of chronic migraines in 2010.[11],[28],[29] Onabotulinum Toxin Type A main mechanism of action is inhibition of acetylcholine neurotransmitter release at presynaptic nerve terminals.[30] Research suggests the inhibition of neurotransmitter release from nociceptive nerve terminals may lend to a possible analgesic effect.[31] Additionally, it is thought that Onabotulinum Toxin Type A may inhibit the release of inflammatory mediators from sensory nerves.[28] According to the American Academy of Neurology guidelines, there is level U (insufficient) evidence for established efficacy of this neurotoxin for the treatment of ON.[11],[32] In reviewing the literature, only two published studies were found evaluating Onabotulinum Toxin Type A specifically as a treatment for ON. Kapural et al. treated six patients with severe intractable ON with 50 U of Onabotulinum Toxin Type A (100 U for bilateral pain). Significant decreases in the pain Visual Analog Scale and improvements in the Pain Disability index were noted in five of the six patients four weeks post-treatment. The duration of pain relief was, on average, 16 weeks.[33] Taylor et al. published a subsequent study with six patients. 12 weeks post-treatment, there was an improvement in sharp, shooting pain and quality of life measurements, but no statistically significant improvement was noted in the dull, aching pain or pins-and-needles-type pain. Additionally, there was no reduction in pain medication usage.[1],[34] As no randomized, blinded clinical trials have been conducted, definitive conclusions cannot yet be drawn from these preliminary data.[32],[35] The senior author (BA) uses Onabotulinum Toxin Type A for treatment of ON using the ART technique, which delivers the Onabotulinum Toxin Type A in a more targeted fashion around the occipital nerves.[36] Pulsed Radiofrequency Ablation (PFRA) PFRA has been proposed as a minimally invasive treatment for ON, although evidence confirming its long-term effects is lacking.[37] The pulsed method was developed as an alternative to continuous radiofrequency lesioning, which has been used to treat various neuralgias but carries a potential risk of post-operative deafferentation pain.[38] PFRA exposes the nerve to a series of short-duration, high voltage pulses.[1],[14],[39] Although the exact mechanism by which PFRA exerts its analgesic effect is unknown, it is theorized that this technique decreases pain by inducing a low-intensity electrical field around sensory nerves, inhibiting long-term potentiation in unmyelinated C fibers and lightly myelinated A-delta fibers, without the thermal coagulation seen with continuous radiofrequency ablation.[11],[37],[40] The electrical field also induces a transmembrane potential that can have significant effects on affected cells, including tissue disruption, ion channel disruption, and threshold potential alterations.[11],[40] Studies have demonstrated short to intermediate pain relief in patients with ON using PFRA.[37] Vanelderen et al. conducted a prospective analysis of 19 patients with ON. 68.4%, 57.9%, and 52.6% of patients reported a pain improvement of at least 50% one, two, and six months post-treatment.[14] Additionally, the median Medication Quantification Scale score declined six months post-treatment. No complications were reported, though the authors argued these results warrant further placebo-controlled studies.[41] Huang et al. also collected retrospective data on 102 patients who underwent PFRA. It is the largest study to date evaluating the effects of this treatment on ON. 51% of patients experienced at least 50% pain relief lasting at least three months. Factors associated with positive outcomes included a traumatic inciting event, lower diagnostic nerve block volumes, and multiple rounds of PFRA.[37] Finally, Cohen et al. performed a randomized, double-blind study comparing PFRA to steroid injections for ON. The authors found that PFRA resulted in a greater reduction in occipital pain at six weeks compared to steroid injections. Worst occipital pain for the patients treated with PFRA was also improved at three months, but the extent of pain relief diminished by six months.[42] Cryoneuroablation (CA) CA is a technique that may be used to treat ON in cases where nerve blocks or steroid injections have failed.[43] This interventional modality involves the application of a cryoprobe to tissues, creating a drastic temperature decrease and resultant conduction block.[44] The extremely low temperature allows ice crystals to form around the nerve, causing vascular damage to the vasa nervorum, resulting in endoneural edema.[44],[45] Disrupting the nerve structure leads to Wallerian degeneration More Details while leaving the myelin sheath and endoneurium intact.[45],[46] It is proposed that the blocked nerve conduction of afferent and efferent pain pathways may alleviate or eliminate neuropathic pain.[44] Furthermore, it has been proposed that the efficacy of CA is proportional to the degree of cold temperature achieved and the length of exposure to that temperature.[46] Traditional CA was performed using landmark guidance and by palpating for the point of maximum tenderness.[44] In a retrospective study evaluating this method, Kim et al. found that among 38 patients treated with CA, the average improvement in pain relief was 57.9%, with a mean duration of 6.1 months, compared to 71.2% pain improvement in patients who received a local anesthetic injection. Two patients reported post-procedural neuritis and one patient was monitored for a procedure-related hematoma.[44] While cryoneurolysis in the traditional procedure was performed at the nuchal ridge, the GON in this region has been found to show large anatomical variation and can be located anywhere between 0.5 and 7.5 centimetres from the midline.[43],[47] Newer methods using imaging guidance have implemented a more proximal injection approach, superficial to the obliquus capitis inferior muscle.[43],[48],[49] Kastler et al. reported that with this CT-guided method, five of seven patients had at least 50% improvement in pain three months post-treatment.[49] Mean intra-procedural pain was less than five out of ten. A limited number of studies, including those with small sample size and brief follow-up period, do not yet allow for definitive conclusions about the technique to be drawn.
Nerve stimulation Occipital nerve stimulation is a minimally invasive, adjustable, and reversible technique first described by Picaza et al. in 1977.[50] The implantable device consists of a subcutaneous regional electrode and pulse generator.[51] It is proposed that stimulation of the distal branches of C2 and C3, and the peripheral extension of the trigeminocervical complex may inhibit central nociceptive impulses.[52] The Neuromodulation Appropriateness Consensus Committee concluded that nerve stimulation for ON is recommendable in cases refractory to conservative medical treatment.[53] Treatment is considered successful if there is a greater than 50% reduction in pain, decrease in the number of headache days, or patient-reported improvement in the quality of life.[51] Implantation can be performed after a trial period using local anesthetic and conscious sedation or general anesthesia.[53] There are two accepted approaches to implantation. In the lateral approach, an incision is made along the mastoid process and the stimulating lead is subcutaneously advanced towards the midline at the level of C1.[15] In the medial approach, a 2 centimeters midline incision is made at the level of C1, and the leads are inserted laterally from that midpoint.[51] The pulse generator can be placed in the upper buttock, abdomen, infrascapular region, or infraclavicular region.[54] The most common complication is lead migration, with a reported incidence varying from a few percent to as high as 100%.[55],[56] Other adverse events include occipital muscle spasms, due to the lead being placed too deeply, lead fracture, infection, skin erosion, and localized pain at the implant sites.[51],[53],[57] PET scans have shown that in chronic migraine patients treated with occipital nerve stimulation, there is increased cerebral blood flow in the treated areas involved in central neuromodulation.[53],[58] The Occipital Nerve Stimulation for the Treatment of Intractable Migraine (ONSTIM) trial was a multicenter, prospective study that randomized patients who responded favorably to occipital nerve block into three groups: adjustable nerve stimulation, preset nerve stimulation, or medical management. Three months post-treatment, the percent reduction in headache days per month was 27.0%, 8.8%, and 4.4% for the groups, respectively.[18] A study by Salmasi et al. found that after eight months post-treatment, average pain was reduced by 50%. One patient developed an adverse reaction to the adhesive of the battery transmitter, but it was not severe enough to discontinue treatment.[59] Finally, Raoul et al. reported that in 60 patients with intractable occipital headaches, 76% had a least a 50% decrease in their pain scores. However, the authors argued that the high frequency of complications must be considered in the surgical decision.[13] C-2 ganglionectomy An older technique not routinely performed is microsurgical C-2 ganglionectomy. Because the C2 ganglion and nerve root lie outside the spinal canal, between the arch of C1 and lamina of C2, C2 sensory neurons and axons may be vulnerable to injury or compression.[60],[61],[62] Dorsal root ganglionectomy removes the primary sensory neuronal cell bodies, and there is no possibility of axonal regeneration.[61] Lozano et al. performed C2 ganglionectomies on 39 patients with intractable occipital pain and found that 19 patients experienced a greater than 90% reduction in pain, while 13 patients experienced treatment failure. Patients with post-traumatic pain reported the most favorable responses. Post-operatively, one patient developed numbness as a result of deafferentation syndrome.[61] Another study by Acar et al. noted that the benefits of C2 ganglionectomy were short-lived, with the average pain relief duration lasting 12 months.[63] Due to limited evidence in favor of this procedure and support of other treatment options, C2 ganglionectomies are not commonly performed for the treatment of ON. Screening patients for surgery In order to identify candidates for surgery, patients must undergo a thorough screening process. Gfrerer et al. discuss one such strategy, summarized below.[64]
The authors' approach to surgical decompression/deactivation of occipital neuralgia The GON can be decompressed using an endoscopic-assisted approach and counter incision, while the LON may be decompressed or avulsed, depending on the size of the nerve. Both procedures are outlined below. Prior to surgery, preoperative markings should be made with the patient in a relaxed, seated position. The GON is generally found 1.5 cm lateral to the midline and 3 cm below the occipital protuberance.[66] However, this varies and should be confirmed with palpation of the tender area before surgery. The LON is 7 cm lateral to the midline and 6 cm inferior to the external auditory canal.[66] As the point of maximum tenderness may not always correlate to these measurements, these areas should also be marked bilaterally. Greater occipital nerve decompression There are six identified compression points of the GON that should be addressed for complete decompression [Figure 1].[3],[64],[67],[68] We also have added several distal vascular dynamic compression points that need to be addressed, and the addition of an endoscope helps with visualization of these areas. The six points of compression are:
There is a close relationship between the GON and OA that has not previously been reported[69]; in particular, there are four compression sites between the GON and OA distally, after the nerve exits the trapezius fascia. This pattern appears to be consistent, as illustrated in [Figure 1]. (A) The OA first approaches lateral to medial and dives under the GON. (B) It then loops from medial to lateral over the GON. (C) The OA then intertwines with the medial branch of the GON. (D) Finally, the OA travels parallel medial branch of the nerve bifurcation at its most distal part. The endoscopic-assisted approach with a counter incision, described below, allows for better visualization of this relationship in order to completely decompress the GON from the OA.[69] The patient is placed on the operating table in the prone position with shoulders taped back [Figure 2]. After injecting lidocaine with epinephrine, a 3-4 cm midline incision is made just below the occipital protuberance [Figure 3].[36] Electrocautery is then used to further open the midline. Underneath the trapezius fascia is the trapezius muscle, whose fibers run lateral and oblique to the midline raphe.[64] The third occipital nerve is often encountered here and can be avulsed using hemostat-assisted traction neurectomy [Figure 4]. In a retrospective study of 229 patients, removal of the third occipital nerve did not alter post-operative results and its removal is therefore appropriate if dissection is difficult.[25]
Deeper dissection leads to the identification of the semispinalis capitis muscle, whose fibers run vertically [Figure 5].[66] The GON can be identified through blunt dissection laterally between the top surface of the semispinalis capitis and underneath the trapezius fascia [Figure 6].[66] A 1 x 1 cm block of the medial semispinalis muscle is excised to prevent future nerve compression.[69] The GON is then decompressed proximally with the full release of the obliquus fascia.
Decompression of GON continues by releasing the trapezius tunnel under direct visualization. At this point, the GON must be released from the OA. The most common approach to decompression of the GON involves limited dissection, manipulation, and cauterization of the OA, as described by Chmielewski et al.[6] However, due to the intimate relationship between the GON and OA, as described above, a counter incision is necessary to completely and safely address the entire segment of the artery compressing the GON. An endoscope assists in detailed visualization of vessels at the proximal points of dynamic compression that otherwise may be missed by the naked eye. The counter incision marking is made obliquely and laterally above the ear following the path of the GON [Figure 7].[66] Electrocautery is performed to dissect down to the nerve. However, once the nerve is visible, blunt dissection must be performed to avoid GON injury. Dissection continues until both the GON and OA are identified. A 30-degree high-definition endoscope is inserted through the midline incision to better visualize the pulsating artery proximally [Figure 8].[69] The artery is dissected off the nerve carefully, and the artery is destroyed with cautery to prevent backflow.
To provide padding and prevent any muscle or fibrous reconstitution around the decompressed GON, a subcutaneous flap of adipose tissue is taken caudally, passed under the GON, and sutured to the midline raphe to wrap and protect the nerve. In patients with a very low BMI and inadequate amount of fat, a nerve protector may instead be used.[66] Lesser occipital nerve decompression/traction neurectomy The LON lies at the posterior border of the sternocleidomastoid muscle [Figure 1] and [Figure 9]a. This nerve can be addressed through decompression or traction neurectomy.
Larger nerves should be decompressed, as any nerve avulsion may have some morbidity. To decompress the LON, adequate exposure is necessary to identify the sternocleidomastoid muscle.[66] The patient is not paralyzed in order to ensure minimal injury to the spinal accessory nerve. The senior author (BA) conducted a study on six cadavers analyzing the anatomical relationship between the lesser occipital nerve, greater auricular nerve, and spinal accessory nerve (SAN) in the posterior triangle of the neck. While there is variable anatomy in this area, the LON is always found caudal to the emergence of the SAN, emerging from a deeper plane behind the sternocleidomastoid muscle.[19] The danger zone during dissection, the point of LON and SAN decussation is often very close to the point of emergence of the LON and at times maybe indistinguishable from the emergence of the SAN.[9] Surgeons approaching the posterior triangle must use caution, especially when using visually limited incisions, blunt dissection, or electrocautery.[19] After dissection down to the LON, if the nerve is noted to be of smaller caliber, it can be avulsed [Figure 9]b. In a randomized prospective study conducted by Guyuron et al., traction neurectomy (avulsion) was found to have equal results when compared to cutting, crushing, and burying.[5] Prior to avulsion, a nerve stimulator should be used to confirm avoidance of the SAN. Post-operative care, residual pain, and refractory cases Post-operative drain removal happens between days two and four. Generally, this operation has minimal morbidity and few complications. Nerve irritation, paresthesia, and hyperesthesia can happen after surgery and usually subsides on their own. Neurontin (gabapentin) and Lyrican (pregabalin) can help with this, as well as a frequent scalp massage. Gentle range of motion physical therapy (ROM PT) will also ease any stiffness. In circumstances of residual pain, patients have the option of Anatomical Regional Targeted Botulinum Toxin (ART-BOTOX). This method, developed by the senior author (BA), focuses on three components: “Anatomical,” based on the anatomical location of nerves known to be causing pain; “Regional,” focusing on areas where pain begins; and “Targeted,” based on the surface topography of the tender area, which may not fully correlate with the expected location due to anatomical variations.[36] This focused delivery is based on the theory that Onabotulinum Toxin Type A may work directly on the nerve to decrease pain, rather than acting indirectly on the muscle alone.[36],[70] The ART technique can be used in other areas in instances of pain shifting from the occipital area to the forehead or temples, which could happen in cases of mixed migraine and ON. For patients with ON, the area of maximum tenderness tends to be 0.5-1 centimeters lateral to the exit point of the GON from the semispinalis capitis muscle, likely due to irritation and compression by the nuchal line and greater occipital vessels.[36] There may be another point of tenderness in the distal ends of the GON or LON as they course over the mastoid and superior areas of the ear, where they intertwine with the OA [Figure 10].[36]
In cases of ON that continue to be refractory despite thorough decompression of the GON, a surgical option is GON excision as described by Ducic et al. During this procedure, a previously decompressed GON can be transected, with excision of the dorsal portion and burial of the proximal end into the nuchal musculature. A retrospective review of 71 patients who underwent GON excision after decompression found that 70.4% experienced at least a 50% reduction in migraine index score. The most common adverse events were numbness or hypersensitivity in the denervated area, occurring in up to 31% of patients.[71]
Occipital neuralgia is a primary headache disorder characterized by sharp, shooting, or electric shock-like pain in the distribution of the occipital nerve. While initial treatment is conservative, surgical management has emerged as a means of addressing refractory pain. The authors have outlined details of an endoscopic-assisted approach to decompress the GON proximally in areas of fibrous and muscular compression, as well as distally by thorough decompression of the occipital artery from the nerve, which is not the gold standard surgical treatment of occipital neuralgia. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
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