Refractory orofacial pain Minimally invasive treatments
Short review
Pathos 2025; 32.4. Online 2025, Dec 13
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Carmelo Costa
Head of Pain Therapy Center Spoke
Humanitas Clinical Institute of Catania,
Emilia Lo Giudice
Anaesthesia and Pain Therapy
Anaesthesia and Pain Therapy
AO Umberto I, Enna
_________________________________________________________________________________
Summary
Orofacial pain encompasses a variety of different and varied pathologies that are difficult to classify. This leads to diagnostic difficulties and, consequently, ineffective treatments. It has an overall prevalence of up to 30 per cent in the general population. Odontogenic pain accounts for almost 60 per cent of cases, meaning that non-odontogenic pain accounts for around 10 per cent. Between 30 and 40 per cent of patients do not respond to conservative treatment, primarily pharmacological. For these patients, minimally invasive percutaneous techniques can be an excellent alternative due to their ease of reproduction, low rate of complications and effectiveness. This article provides an overview of the most common techniques, highlighting their salient features and controversial points, to facilitate their dissemination.
Riassunto
il dolore orofacciale comprende una serie di patologie variegate ed eterogenee di difficile classificazione e questo comporta difficoltà diagnostiche e conseguenti ripercussioni su terapie poco efficaci. Ha una prevalenza complessiva che arriva fino al 30 per cento nella popolazione generale. Quasi il 60 per cento è costituito dal dolore odontogeno e quindi il dolore non odontogeno rappresenta circa il 10 per cento. Il 30-40 per cento di questa popolazione è refrattaria al trattamento conservativo, prevalentemente farmacologico. Per questi pazienti le tecniche percutanee mininvasive possono rappresentare un'eccellente alternativa in considerazione della loro facile riproducibilità, bassa percentuale di complicanze ed efficacia. Riportiamo una panoramica delle tecniche più diffuse evidenziandone gli aspetti salienti e i punti controversi onde facilitarne la diffusione.
Key words
Pain, orofacial, refractory, drugs, techniques, mininvasive
Parole chiave
Dolore orofacciale, refrattario, farmaci, tecniche mininvasive
Introduction
Orofacial pain consists of a heterogeneous set of pathologies. Pain can be a symptom, as in odontogenic pain, or part of a dysfunctional condition, as in disorders of the muscles and temporomandibular joint, or constitute the pathology itself (disease-pain), as in many painful trigeminal neuropathies, or be part of a syndromic condition, as in persistent idiopathic facial pain or burning mouth syndrome.
For this reason, orofacial pain is difficult to diagnose correctly and, consequently, to treat successfully: the many existing classifications are proof of this.
From an epidemiological point of view, the prevalence of orofacial pain in the adult population is estimated to range between 16 and 30 per cent. Of this percentage, less than 60 per cent is attributable to odontogenic pain. Therefore, even considering the difficulties of conducting reliable statistical studies on such a varied and heterogeneous sample, 7 to 10 per cent can be attributed to non-odontogenic pain. In the latter group, pain originating from temporomandibular muscle and TMJ dysfunction, neuropathic pain and idiopathic pain should be considered.
Orofacial pain refractory to pharmacological treatment accounts for 30 to 40 per cent of cases, with a significant 25 per cent of patients having tried 4 to 9 different treatment regimens without obtaining any pain relief. However, this 30-40 per cent does not refer to orofacial pain as a whole, but only to non-odontogenic pain, as odontogenic pain usually responds well to dental and surgical treatment. In any case, refractoriness should be understood as a failure to reduce pain following conservative treatments in the broad sense and not only pharmacological treatments, such as acupuncture, cognitive-behavioural therapy and mindfulness.
In refractory cases, non-invasive neuromodulation procedures such as transcranial magnetic stimulation (TMS) or focused ultrasound stimulation (FUS) may be considered, or, conversely, major surgical procedures such as microvascular decompression in cases of neurovascular conflict affecting the V or IX cranial nerves. In
this article, we will only examine minimally invasive percutaneous techniques that are part of the cultural heritage of algologists.
There are three main neurological targets for minimally invasive interventional treatments:
- the trigeminal-cervical system
- the sphenopalatine ganglion
- the glossopharyngeal nerve
1) Procedures involving the trigeminal-cervical system are the most numerous and effective, partly because the trigeminal nerve (the fifth pair of cranial nerves) innervates most of the face from a sensory point of view, with the exception of the angle of the jaw (innervated by the great auricular nerve, branch of C2-C3) and most of the ear, of which the trigeminal nerve innervates only the ascending part of the helix and part of the tragus with the auriculotemporal nerve (branch of the mandibular nerve, third trigeminal branch V3). In addition to the sensory innervation of the face, the trigeminal nerve also innervates the masticatory muscles (temporal, masseter, lateral and medial pterygoid) as well as the tensor veli palatini and tensor tympani muscles. The motor root travels together with the fibres of V3, which is therefore the only mixed root, as the first two, V1 and V2, are completely sensory. The three branches afferent to the Gasserian ganglion (anatomical equivalent of the spinal ganglion and seat of the first sensory neuron) then continue with the retrogasserian root to the pons and medulla oblongata or bulbus. Here, from top to bottom, are the mesencephalic nucleus, where the proprioceptive fibres arrive, the main pontine sensory nucleus, to which the tactile sensitivity fibres afferent, and the descending trigeminal nucleus, which is in turn divided into three sub-nuclei (from top to bottom: oral, interpolar and caudal sub-nuclei).
The second nociceptive neuron is located in the trigeminal descending nucleus, especially in the caudal subnucleus. The extreme part of the trigeminal descending nucleus makes anatomical contact with the central terminals of the first three cervical nerves. From a physiological point of view, it represents a convergence of nociceptive stimuli between the face and the cervical structures innervated by the first three cervical nerves.
In such a large and complex anatomical structure, interventional procedures can be divided according to the specific site where they are performed. Thus, we will distinguish from the periphery to the centre:
A) peripheral nerve blocks performed in the postganglionic site
B) techniques on the trigeminal-Meckel's cave compartment (Gasser's ganglion and retrogasserian cistern) for post-traumatic and infectious trigeminal neuropathies and trigeminal neuralgia, respectively.
C) procedures on the occipital nerves (infiltrative, neuromodulatory and neurostimulatory)
D) placement of upper cervical medullary stimulators (with tip between C1/2).
Peripheral nerve blocks
These reliable diagnostic and therapeutic tools are used to treat painful syndromes of the head and face, as well as intractable headaches. One advantage is that they can be performed using simple external skin references, without the need for imaging tools such as X-rays, CT scans or ultrasounds. However, their main limitation is the lack of consensus among practitioners on how to perform them, including the type, dose and volume of drugs and the frequency of nerve blocks. Usually, a mixture of local anaesthetics and/or steroids in a volume of a few millilitres (3–5) is administered every two to three weeks until the symptoms resolve.
Clearly, the mechanism of action is not the same as that which causes surgical anaesthesia. Otherwise, it would be impossible to explain how an injection of just a few millilitres of local anaesthetic could provide weeks-, months-, or even permanent analgesia. The most likely mechanism involves altering the nociceptive process along certain transmission pathways, such as the trigeminal-cervical complex. These blocks have a success rate ranging from 55% to 84% in treating refractory orofacial pain, depending on the type and location of the neuralgia, with better results seen in well-defined neuralgias/neuropathies and worse results in persistent idiopathic facial pain (PIFP).
In more complex and refractory cases of postherpetic, traumatic, or idiopathic trigeminal neuropathies, subcutaneous electrocatheters may be implanted to stimulate the supraorbital and infraorbital nerves. These have a success rate of approximately 70–80 per cent in reducing pain by at least 50 per cent, although there are no randomised controlled studies.
Complications such as skin erosion, infection and electrode.
Techniques for the trigeminal compartment (Gasserian ganglion and retrogasserian cistern)
Although there is no consensus among practitioners, it is now well established that continuous radiofrequency (CRF) applied to the trigeminal cistern (located a few millimetres posterior to the Gasserian ganglion), where the three trigeminal roots remain anatomically and functionally separate, is an effective treatment for trigeminal neuralgia.
For trigeminal neuropathies (both post-traumatic and post-infectious), the preferred technique is pulsed radiofrequency (PRF).
Although it is less effective than CRF in terms of percentage pain reduction, number of patients treated and duration of pain relief, PRF is safe and practical for treating neuropathic pain. There is agreement that the spinal and cranial ganglia are excellent targets for PRF. Nevertheless, the numerous scientific articles that refer to neuromodulation of the Gasserian ganglion do not detail any measures aimed at the difficult task of reaching the ganglion with the radiofrequency needle. The correct technique is always described as one in which the sensory paresthesia in the test overlaps with the area of pain.
On the other hand, reaching the Gasserian ganglion should be detected by other clinical signs, such as paresthesia evoked in all three trigeminal branches as the voltage increases.
In the case of trigeminal neuralgia, initial pain relief is experienced by 70-100% of patients, with pain disappearing and anticonvulsant medication being discontinued. The duration of this relief is usually around 2-3 years. However, longer-lasting results can be achieved by performing more extensive thermal lesions.
Although the results of PRF on neuropathies are less impressive, they are still satisfactory considering the typical refractoriness of these painful syndromes to conservative treatment. It is estimated that 55–86% of patients experience at least a 50% reduction in pain for 6–12 months.
Procedures on the occipital nerves
These procedures always target the greater occipital nerve (GON), either on its own or alongside the lesser occipital nerve, the third occipital nerve and the greater auricular nerve. These nerves all originate from C2-C3 and are therefore an integral part of the trigeminal-cervical complex. However, the GON is the primary target. It is the medial branch of the dorsal branch of C2 and emerges between the atlas and the epistropheus. The GON is a purely sensory nerve branch; the motor component is transmitted by the lateral branch of the dorsal branch. The GON can be accessed at a deep site, beneath the inferior oblique muscle of the head, before the first curve. In this case, CT guidance is required, as is a steroid anaesthetic block. After the first curve of the nerve (the intermediate site), infiltration can be performed with ultrasound guidance, or with radiofrequency guidance if the nerve is clearly visible. Finally, at the superficial site, where the nerve emerges from the aponeurosis of the trapezius muscle and becomes subcutaneous at the occiput, the GON can be blocked using external markers. However, ultrasound guidance is always recommended to improve accuracy, especially when RF thermolesion is chosen. Anaesthetic infiltration performed using the 'fan' technique can compensate for a lack of precise nerve identification.
The main indications are occipital neuralgia, cervicogenic headache, chronic refractory migraine (with pain mainly localised in the occipital region) and cluster headache. GON procedures consist of an anaesthetic-steroid block, which is the preferred method for diagnosis and short-term relief (lasting on average 3–4 weeks). They are more effective in treating neuralgia, particularly occipital neuralgia, and less effective in treating other types of pain, such as persistent idiopathic facial pain. In general, the percentage of patients experiencing a pain reduction of at least 50 per cent ranges from 55 to 100 per cent. If pain recurs within a short period or a longer-lasting effect is desired, continuous radiofrequency neuroablation can be used, particularly for occipital neuralgia or cervicogenic headache when pain is localised to the occipital region without significant anterior extension and when there is a traumatic aetiology. In these cases, pain reduction occurs in 51–89% of patients for an average duration of 5–6 months.In cases that are resistant to both blocks and radiofrequency (RF) therapy, peripheral nerve stimulation (PNS) of the occipital nerves is used, either with or without a positive GON block diagnostic test. In carefully selected cases, a significant reduction in pain is achieved in 69–93 per cent of patients three months after implantation, with the benefit being maintained in a smaller percentage of patients in the long term.
Upper cervical spinal cord stimulation
Techniques used for pain resistant to blocks and radiofrequency
For more complex cases of trigeminal neuropathic pain, such as post-traumatic or post-infectious trigeminal neuropathy, trigeminal neuralgia secondary to multiple sclerosis or deafferentation trigeminal neuropathy (provided that complete pain anaesthesia has not been achieved), a cervical spinal cord stimulator with a C1-2 tip can be used. This is particularly useful if other neuromodulation methods, such as pulsed radiofrequency of the Gasserian ganglion, have failed to provide adequate pain relief. This technique works by indirectly stimulating the descending trigeminal nucleus, which receives trigeminal nociceptive afferents from the craniofacial region. Additionally, afferent fibres from the vagus and glossopharyngeal nerves reach the paratrigeminal nucleus where they integrate with trigeminal fibres. This contributes to both nociceptive transmission and autonomic reflexes. This integration represents the anatomical and functional basis for the cross-modulation of pain and the phenomenology of referred pain in the cranio-cervical region. Furthermore, stimulation of vagal afferents can modulate the activity of trigeminal neurons, either inhibiting or facilitating orofacial pain transmission.
The success rate of significantly reducing pain (by at least 50 per cent) is between 50 and 70 per cent for patients, with a success rate of over 50 per cent after permanent implantation. The long-term failure rate (defined as loss of efficacy or complications) is 25 per cent.
Techniques performed on the sphenopalatine ganglion have fewer and less certain indications than those performed on the cervical trigeminal system. Apart from anecdotal evidence or cases targeting distant areas or unlikely pathologies (such as chronic low back pain, fibromyalgia, asthma and sacroiliac pain), the most compelling indications are cluster headaches and, more generally, trigeminal autonomic cephalalgias (TACs), of which cluster headaches are the most prevalent. Less convincingly, these techniques are also used to treat persistent idiopathic facial pain (PIFP).
The sphenopalatine ganglion, located in the upper part of the pterygopalatine fossa, is the largest parasympathetic ganglion outside the cranial cavity. Located in the upper part of the pterygopalatine fossa, it is anteriorly bounded by the maxillary sinus and posteriorly by the pterygoid process of the sphenoid bone. Medially, it is enclosed by the perpendicular lamina of the palatine bone and, superiorly, by the sphenoid sinus. Laterally, it opens into the infratemporal fossa. The fossa also communicates with the nasal cavities via the nasopalatine or sphenopalatine foramen, located posterior to the middle turbinate. This allows drugs administered nasally, usually local anaesthetics, to reach the sphenopalatine ganglion.
The maxillary nerve (the second trigeminal branch, V2) is located superior to the GSP just after exiting the foramen rotundum, and the two structures communicate through the pterygopalatine nerves. Posteriorly, the ganglion is reached by the vidian nerve, which carries postganglionic sympathetic and preganglionic parasympathetic fibres. The latter synapse within the GSP and continue to the nasal mucosa. One branch travels with the maxillary nerve to the lacrimal gland.
A cluster headache is characterised by intense pain lasting from 15 to 180 minutes. It is localised unilaterally in the orbital, retro-orbital and temporal areas, and is accompanied by dysautonomic phenomena such as conjunctival redness, lacrimation, eyelid ptosis, rhinorrhoea and a feeling of nasal obstruction. It is also accompanied by significant psychomotor agitation. This makes it easy to distinguish a cluster headache from a migraine, in which the patient prefers to remain still in a dark, silent environment. Furthermore, cluster headache is one of the few types of facial pain that predominantly affects men. There is a sporadic form affecting around 90 per cent of patients, and a chronic form with a worse prognosis and greater resistance to pharmacological and invasive treatments affecting the remaining 10 per cent.
Conclusion
The percentage of patients with non-odontogenic orofacial pain who are refractory to conservative treatment is high, ranging from 30 to 40 per cent. Furthermore, pharmacological treatments frequently result in adverse effects that are challenging to tolerate and which have a detrimental effect on patients' quality of life. Refractory pain should be conceptualised in this manner rather than as a lack of response to therapy. Concurrently, minimally invasive techniques have undergone substantial refinement. This advancement can be attributed to the instruments employed for their execution, namely novel radiofrequency generators and needles of reduced thickness, which are more appropriate due to their diminished size and inherent characteristics. Furthermore, the utilisation of imaging modalities such as ultrasound has contributed to this progress, as they do not carry the risk of ionising radiation exposure to the patient. In this novel perspective, rigorous studies conducted on a sufficient number of patients and with control would be advantageous to confirm the use of the aforementioned techniques. It is imperative that these techniques are executed in a complementary and non-sequential manner in relation to pharmacologic treatment.
Conflict of interests
The authors declare that the article was written without any conflict of interest.Open Access-license (CC BY-NC 4.0)
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Published
13 th December 2025
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