The addition of head and neck blocks to a pain management physician’s skill set can be rewarding for the practitioner as well as the patient. An understanding of the complex anatomy of this region of the body is absolutely necessary to improve the success of the block as well as to minimize potential complications. Both fluoroscopy and ultrasound can be utilized to identify the target and administer treatment. To improve on the success and duration of the diagnostic/therapeutic block, neurolytic procedures can be performed.
Keywordsanatomy, complications, fluoroscopy, nerve block, ultrasound
Nerve blocks of the head and neck can be rewarding procedures for any anesthesiologist or pain management practitioner. The blocks can be used for regional anesthesia and postoperative pain control as well as for diagnostic and therapeutic purposes for managing chronic pain. In the algorithm for treating chronic pain, the blocks are indicated when pharmacologic therapy is partially effective or ineffective in alleviating a patient’s pain. Detailed knowledge of the relevant anatomy and the use of fluoroscopy and ultrasound will theoretically improve efficacy and minimize complications.
Indications and Contraindications
Specific indications are listed with the individual blocks. Informed consent prior to the block is a necessity. Absolute contraindications include patient refusal, local infection, sepsis, and increased intracranial pressure (trigeminal ganglion block). Relative contraindications are coagulopathy, anticoagulant therapy, history of facial and neck trauma (potential for altered anatomy), and preexisting neurologic deficits. Prior to stopping any anticoagulant therapy, consult the prescribing physician for guidance. Drug-eluting cardiac stents should also be considered. Allergy to medications used can be absolute or relative depending on the severity of the allergy. Pretreatment with H1 and H2 receptor blockers plus corticosteroids may be necessary.
Trigeminal Nerve and Ganglion
The trigeminal ganglion resides in the middle cranial fossa. It is situated in a fold of dura mater that forms an invagination around the posterior two-thirds of the ganglion. This region is referred to as Meckel’s cavity and contains cerebrospinal fluid. The ganglion is bound medially by the cavernous sinus and optic and trochlear nerves, superiorly by the inferior surface of the temporal lobe of the brain, and posteriorly by the brain stem. The ganglion is formed by the fusion of a series of cell bodies that originate at the midpontine level of the brain stem. The ganglion has three major divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3). The ophthalmic division is located dorsally, the maxillary branch intermediate, and the mandibular branch ventrally. The ophthalmic division leaves the ganglion and passes into the orbit through the superior orbital fissure. It further divides into the supraorbital, supratrochlear, and nasociliary nerves, which innervate the forehead and nose. The maxillary division exits the middle cranial fossa via the foramen rotundum, crosses the pterygopalatine fossa, and enters the orbit through the inferior orbital fissure. Branches include the infraorbital, superior alveolar, palatine, and zygomatic nerves, which carry sensory information from the maxilla and overlying skin, the nasal cavity, palate, nasopharynx, and meninges of the anterior and middle cranial fossa. The mandibular division exits through the foramen ovale and divides into the buccal, lingual, inferior alveolar, and auriculotemporal nerves. These nerves carry sensory input from the buccal region, the side of the head and scalp, and the lower jaw, including teeth, gums, anterior two-thirds of the tongue, chin, and lower lip. The motor component of V3 innervates the masseter, temporal, medial, and lateral pterygoid muscles. The ganglion interfaces with the autonomic nervous system via the ciliary, sphenopalatine, otic, and submaxillary ganglia. It also communicates with the oculomotor, facial, and glossopharyngeal nerves (GNs).
Ophthalmic Nerve Block
Two of the terminal branches of the ophthalmic division can be blocked as they exit their respective foramina for pain in the forehead. The supratrochlear nerve exits its foramen on the medial aspect of the superior orbital ridge, whereas the supraorbital nerve exits its foramen in the middle of the superior orbital ridge. After sterile prep, palpate the foramen and subcutaneously inject 1–2 mL of local anesthetic over the foramen. If the pain is alleviated, cryoneurolysis of the nerve or nerves can provide long-lasting relief.
Maxillary Nerve Block
Diagnostic and therapeutic blocks of the maxillary nerve are performed similarly. Fluoroscopy is not always necessary, but it may be used when external landmarks are not easily palpated or when a neurolytic technique is planned. The most common indication for this block is regional anesthesia for surgery of the upper jaw, but it is also effective for acute postoperative pain control. In the pain management arena, it is indicated for the diagnosis and treatment of chronic pain in the distribution of the maxillary division of the trigeminal nerve.
For localized pain, the infraorbital nerve can be blocked as it exits its foramen below the inferior orbital ridge. After sterile prep, palpate the foramen subcutaneously and inject 1–2 mL of local anesthetic over the foramen.
To block the maxillary division, place the patient in the supine position. Palpate the mandibular notch located below the zygoma and anterior to the temporomandibular joint. Under sterile conditions, anesthetize the skin over the notch. Insert the block needle (usually a 22-gauge 8–10-cm short-bevel or a same-size curved blunt needle) in a horizontal plane through the mandibular notch until bone (lateral pterygoid plate) is touched (typically 4–5 cm) ( Fig. 82.1 ). If a blunt needle is used, an 18-gauge 1.25-inch angiocatheter is inserted first. Withdraw the needle and redirect it anteriorly and superiorly through the pterygomaxillary fissure into the pterygopalatine fossa. Advance the needle approximately 0.25–0.5 cm, at which depth a paresthesia is usually perceived in the upper lip or teeth. If this procedure is performed under fluoroscopy, the needle is angled toward the superior portion of the pterygopalatine fossa, which appears as a “V” on the lateral image. On an anteroposterior image, the needle tip should be above the level of the middle turbinate. At this point inject 3–5 mL of local anesthetic. If fluoroscopy is used, 0.5–1.0 mL of contrast can be injected first to rule out intravascular placement of the needle. Remove the needle and apply an ice pack to the cheek.
Neurolytic blocks can be done with 6% phenol or absolute alcohol. After appropriate placement of the needle, up to 1.0–1.5 mL of the neurolytic solution is injected in 0.1-mL aliquots. The needle should then be flushed with 0.5 mL of saline prior to removal. Pulsed radiofrequency lesioning can also be performed after a successful diagnostic block. Sensory stimulation is performed at 50 Hz, 1 V. Paresthesia in the upper teeth should be perceived at less than 0.3 V. Once confirmed, two or three 120-second pulsed radiofrequency cycles are administered at 45 V.
Mandibular Nerve Block
Diagnostic and therapeutic blocks of the mandibular nerve are both performed in the same manner. Fluoroscopic guidance is not a necessity but is encouraged when a therapeutic block is planned, as it can facilitate needle positioning. Indications are similar to those for the maxillary nerve block except that the area to be anesthetized or treat pain is the lower jaw and tongue.
The procedure is performed identically to the maxillary nerve block except for the following: once the lateral pterygoid plate has been touched with the block needle, withdraw it and redirect in a slightly caudal and posterior direction until a paresthesia is produced in the lower lip, lower jaw, or ipsilateral tongue or ear ( Fig. 82.2 ). The depth should not be more than 0.1–0.25 cm beyond the depth at which the lateral pterygoid plate was contacted. The total distance should not exceed 5.5 cm. If a paresthesia is not elicited at a depth of 5.5 cm, the needle should be withdrawn and redirected.
After proper positioning, inject 2–3 mL of local anesthetic, remove the needle, and apply an ice pack to the side of the face. If using fluoroscopy, start with a lateral view and proceed using the same technique as already described. Since this technique involves blocking the nerve as it exits the foramen ovale, a submental oblique view can be obtained (described later in this chapter under Trigeminal Ganglion Block) in order to verify the position of the needle tip in relation to the foramen ovale. The needle tip should be adjacent to, or overlie, the shadow of the foramen ovale. To rule out intravascular or intrathecal injection, inject 0.5–1.0 mL of contrast. If negative, inject the aforementioned volume of local anesthetic.
Chemical neurolysis can be achieved using 6% phenol, 50% glycerol, or absolute alcohol. After a successful diagnostic block and after proper positioning of the needle, up to 1.0 mL of the neurolytic solution is injected in 0.1-mL increments. Flush the needle with 0.5 mL normal saline before removing it.
For pulse radiofrequency lesioning, perform sensory and motor stimulation at 50 Hz, 1 V, and 2 Hz, 2 V, respectively, to check needle position. Paresthesia should be obtained at less than 0.3 V and masseter contraction should be apparent at less than 0.6 V. There is no consensus on the number of pulse cycles that should be performed, but 2–4, 120-second cycles should be carried out at 45 V.
Tic douloureux is the most common indication for trigeminal ganglion blockade. The block is indicated for patients who have failed conventional pharmacologic therapy and are deemed noncandidates for surgical microvascular decompression. Secondary trigeminal neuralgias from injury to the major divisions or the distal branches of the ganglion are a frequent indication. Palliation of cancer-related pain has been accomplished through blockade of the trigeminal ganglion or its divisions. This block has also found a niche in the treatment of chronic, intractable cluster headaches. Persistent idiopathic facial pain (formerly called atypical facial pain) also responds to ganglion blockade and neurolysis.
As with most current fluoroscopically guided block techniques, the original description of the trigeminal ganglion block utilized external landmarks and a blind approach. The pupil in the midline and the external auditory meatus helped guide the practitioner to the target. Since the use of fluoroscopy is stressed in this chapter to improve the accuracy and success of the block as well as to decrease the chance of complications, the blind approach is not discussed, but knowing the external landmarks can be helpful if the foramen ovale is hard to visualize. The description of this block focuses on the use of a 20- to 22-gauge curved blunt needle, but sharp spinal or block needles are also acceptable.
Obtain intravenous access. Place the patient on the table in the supine position with the head slightly extended. Light sedation with midazolam and fentanyl is usually required, but propofol may be necessary. Using sterile procedure, prepare and drape the appropriate side, leaving the eye exposed. Utilizing continuous or pulsed fluoroscopy, locate the foramen ovale by rotating the C-arm image intensifier obliquely away from the nose approximately 20–30 degrees and then angle the C-arm image intensifier approximately 30–35 degrees in the caudocephalad direction to bring the foramen ovale into view. Subtle adjustments of the C-arm angles may be necessary. Raise a skin wheal directly over the shadow of the foramen, which will be approximately 2–2.5 cm lateral to the corner of the mouth. Insert a short, 16- or 18-gauge angiocatheter through the skin wheal and advance to the hub. Insert a gloved finger into the oral cavity to confirm that the buccal mucosa has not been breached. Reglove before proceeding. Insert a 20- or 22-gauge, curved blunt block needle through the angiocatheter and advance a few centimeters. Obtain a fluoroscopic image to check the trajectory of the needle. The goal is to advance the needle in a coaxial fashion toward the foramen ovale ( Fig. 82.3 ). Corrections in trajectory can be made by turning the needle tip in the appropriate direction. With respect to external landmarks, the trajectory of the needle will be in a plane slightly superior to the external auditory meatus and medially toward the pupil in the midline. Advance the needle in 1- to 2-cm increments until bone is touched. Obtain a lateral image to check the position of the needle. If the foramen has not been traversed, adjust the needle tip (usually posterior) and advance through the foramen a distance of 0.5–1.0 cm ( Fig. 82.4 ). Do not advance the needle tip past the shadow of the clivus. The depth of the needle tip is not as important with a local anesthetic block as it is for a neurolytic procedure. After a negative aspiration for cerebrospinal fluid or blood, inject 0.5–1.0 mL of nonionic water-soluble contrast to confirm position and filling of Meckel’s cavity. Any vascular runoff requires repositioning of the needle. If cerebrospinal fluid is obtained, the needle tip can be withdrawn until fluid is no longer appreciated. If an abundant cerebrospinal fluid leak is present, the remainder of the procedure should be halted. With a significant leak, a high spinal block can be caused with even low volumes of local anesthetic. A small leak of cerebrospinal fluid may or may not cause a high spinal block; if such is present, the pain practitioner should proceed with caution. Inject local anesthetic in volumes of 0.25–0.5 mL at a time, up to 1–2 mL, and observe for effect. Remove the needle and apply an ice pack to the cheek to decrease swelling.
After a successful diagnostic block, a neurolytic procedure can be planned. Needle placement for all neurolytic procedures except balloon microcompression is performed in the same manner as for the local anesthetic block. Heavier sedation may be required for radiofrequency techniques.
For conventional radiofrequency lesioning, a 3- to 5-mm active-tip needle is placed. The target depth of the needle tip depends on the division of the trigeminal nerve that is to be lesioned. The mandibular division is rostral and lateral; the maxillary division is intermediate; and the ophthalmic division is mostly cephalad and medial. Location of the needle tip on the appropriate division or divisions is determined by the response to sensory and motor stimulation (50 Hz, 1 V, and 2 Hz, 2 V, respectively) of the ganglion. Paresthesia should be perceived at less than 0.3 V, with little to no muscle contraction of the masseter muscle at 0.6–1.0 V. If no contraction is seen, then the tip of the needle is on the ophthalmic or maxillary divisions. Once the patient senses paresthesia in the painful area, inject 0.5 mL of 0.25% bupivacaine or 0.2% ropivacaine with steroid. Wait 30–60 seconds and begin lesioning at 60°C for 90 seconds. If the patient cannot tolerate the lesioning, stop and wait an additional 30 seconds, then try again or add another 0.5 mL of local anesthetic prior to resuming lesioning. If more than one branch of the trigeminal nerve is affected, perform several lesions of the ganglion. Reposition the needle and repeat the stimulation test to get paresthesia in the desired site. For lesioning of the ophthalmic division, assess the corneal reflex during and after each lesion. Lesioning is typically started at temperatures of 55°C–65°C to preserve this reflex. One or two lesions are recommended. If the corneal reflex diminishes, lesioning should be stopped.
Pulsed radiofrequency is not a temperature-dependent technique. It is a nondestructive method of providing long-term pain relief. After proper positioning of the needle tip, perform 2–4 pulsed radiofrequency cycles for 120 seconds each at 45 V. The temperature of the needle tip rarely exceeds 42°C; thus local anesthetic is not required. If significant masseter contraction is noted during pulsing, inject 1–2 mL of local anesthetic to diminish this, or hold the patient’s mouth closed with your hand while the cycles are completed.
Chemical neurolysis has been performed with phenol and alcohol in the past, but their use is not currently recommended if radiofrequency lesioning is available. Glycerol is the chemical neurolytic of choice. Once through the foramen ovale, advance a sharp needle until cerebrospinal fluid is observed returning through the needle. Place the patient in a semisitting position with the neck flexed. Inject water-soluble nonionic contrast solution in 0.1-mL aliquots (up to 0.5 mL) into the trigeminal cistern. Failure of visualization or diffusion of the contrast requires repositioning the needle. Once the cistern is visualized, draw back the contrast material by free flow. The flow of contrast is slower than that of cerebrospinal fluid. Inject the same amount of glycerol into the cistern. Flush the needle with 0.5 mL of saline prior to removal. Keep the patient in a semisitting position for 2 hours. During the procedure, patients often report pain, burning, or paresthesia in the affected divisions.
With the exclusion of sensory loss (an expected side effect), radiofrequency thermal lesioning had the highest number of complications (29.2%), followed by glycerol rhizotomy and balloon compression at 24.8% and 16.1%, respectively, for all neurolytic techniques. Retrobulbar hematoma is possible if the needle is advanced into the retrobulbar space. Exophthalmos develops secondary to bleeding in the retrobulbar space. Cheek hematoma can occur if a blood vessel is punctured during placement of the needle. Masseter weakness can develop, especially with lesioning of the mandibular division. The incidence is highest with balloon microcompression (66%) and less for radiofrequency lesioning and glycerol rhizotomy (24% and 1.7%, respectively), but it usually resolves after 12 months. Loss of the corneal reflex, keratitis, ulceration, and hypesthesia are observed in 3%–15% of patients after a neurolytic procedure. Keratitis has been more likely to occur after radiofrequency lesioning and glycerol neurolysis. Corneal anesthesia was highest for radiofrequency rhizotomy at 7% and was observed with glycerol rhizotomy and balloon compression at 3.7% and 1.5%, respectively. Anesthesia dolorosa (deafferentation pain) occurs in up to 4% of patients who have undergone RFTC, followed by glycerol, where it occurs in 2% of cases. Other complications include meningitis, dural arteriovenous fistulas, rhinorrhea, transient cranial nerve deficits, tissue sloughing, and even death. Postprocedure trigeminal nerve sensory loss is an expected occurrence after a properly performed neurolytic procedure. The incidence of this with radiofrequency rhizotomy is as high as 98%, followed by balloon compression (72%) and glycerol neurolysis (60%).
Ultrasound Guided Trigeminal Nerve Block
The branches of the trigeminal nerve, especially the second (maxillary, V2) and the third (mandibular, V3), can be blocked after they exit from the base of the skull through their respective foramina. The maxillary nerve (V2) exits the base of the skull through the foramen rotundum to travel laterally through the pterygopalatine fossa and enter the infraorbital fissure. Injecting a small amount of local anesthetic in the pterygopalatine fossa in close proximity to the foramen rotundum will result in a retrograde spread of the injectate to the gasserian ganglion, which results in blockade of the branches of the trigeminal nerve. In addition, all the contents of the fossa will be blocked, including the sphenopalatine ganglion.
The pterygopalatine fossa is bounded anteriorly by the maxillary bone, superiorly by the sphenoid bone, and posteriorly by the lateral pterygoid plate; it is covered laterally by the lateral pterygoid muscle. The upper head of the lateral pterygoid muscle originates from the infratemporal portion of the sphenoid bone and inserts on the capsule of the temporomandibular joint. Injection of local anesthetic posterior to the maxilla, anterior to the lateral pterygoid plate, and deep to the lateral pterygoid muscle through the pterygopalatine fissure will result in blockade of the trigeminal nerve.
Ultrasound guidance provides excellent visualization of these bony and muscular structures. In addition, the tortuous maxillary artery and vein, which accompany the maxillary nerve, can easily be identified and spared.
The patient is placed in the lateral decubitus position and standard American Society of Anaesthesiologists (ASA) monitoring is applied. The area below the zygomatic bone is cleaned and prepped. A high-frequency small-print linear probe is selected. If the patient exhibits any signs of facial allodynia, an intravenous access is secured and sedation administered. The infrazygomatic area is scanned anterior to the condylar process in the coronoid notch. The acoustic reflections of the maxillary bone and lateral pterygoid plate are identified ( Fig. 82.5 ). The upper head of the lateral pterygoid muscle is identified. The maxillary artery is identified. The needle is directed from lateral to medial and from posterior to anterior toward the pterygopalatine fissure. The needle tip is placed at the fissure. At this point the entire needle trajectory can be visualized. A total of 5 mL of local anesthetic and steroid is injected through the pterygopalatine fissure below the lateral pterygoid muscle. The patient is monitored for 20 minutes for signs of local anesthetic toxicity or extensive local anesthetic spread. Pulsed radiofrequency ablation of the maxillary nerve has been described using this approach.
Although no major complications have been reported from this technique, injection of local anesthetic near the pterygopalatine fossa can result in an intravascular injection, worsening of the symptoms due to an intramuscular injection (lateral pterygoid muscle), or extensive spread of the local anesthetic to basal structures of the brain. Damage to the maxillary artery can result in jaw atrophy. Repeated steroid injection can result in deleterious side effects including atrophy at the injection site.
The ganglion resides in the pterygopalatine fossa. The fossa is bordered anteriorly by the maxillary sinus, posteriorly by the medial pterygoid plate, medially by the palatine bone, and superiorly by the sphenoid sinus. The pterygomaxillary fissure allows passage of a needle into the fossa, while the pterygopalatine foramen is located medial to the ganglion and is just posterior to the middle turbinate. The fossa is approximately 1 cm wide and 2 cm high and appears as a V -shaped structure on a lateral fluoroscopic image. A large venous plexus overlies the fossa. The foramen rotundum and pterygoid canal are located on the superolateral and inferomedial aspects of the fossa, respectively. The maxillary artery resides in the fossa. The ganglion is “suspended” from the maxillary nerve by the pterygopalatine nerves and is medial to the maxillary nerve. Posteriorly the ganglion is connected to the vidian nerve, which is formed by the deep petrosal (sympathetic from the upper thoracic spinal cord) and greater petrosal (parasympathetic from the superior salivatory nucleus) nerves. The ganglion has efferent branches and forms the superoposterior lateral nasal and pharyngeal nerves. Caudally, the greater and lesser palatine nerves exit the ganglion. Sensory fibers arise from the maxillary nerve, pass through the sphenopalatine ganglion (SPG), and innervate the upper teeth, nasal membranes, soft palate, and some parts of the pharynx. A small number of motor nerves are believed to travel with the sensory trunks.
Indications for sphenopalatine ganglion block and neurolysis include sphenopalatine neuralgia, trigeminal neuralgia, migraine headaches, cluster headaches, atypical facial pain, and cancer of the tongue and floor of the mouth. Other reported but not yet mainstream therapeutic uses include sinus arrest in postherpetic neuralgia, vasomotor rhinitis, complex regional pain syndrome of the lower extremity, low back pain, and posttraumatic headache.
The intranasal SPG block can be safely performed in an office setting. The location of the SPG in relation to the middle turbinate as well as the lateral nasal mucosa allows absorption of local anesthetic from a cotton-tipped applicator inserted into the nares. Four percent cocaine is the local anesthetic of choice secondary to its inherent vasoconstrictor property. If this is not available or contraindicated, 1% or 2% lidocaine or 0.25%–0.5% bupivacaine or ropivacaine can be used instead. If these are chosen, the practitioner can pretreat the nares with neosynephrine to produce vasoconstriction. Place the patient in the supine position. Estimate the depth of insertion by externally measuring the distance from the opening of the nares to the mandibular notch. Place a mark corresponding to this depth on the shaft of the cotton-tipped applicator. Soak the applicators in the local anesthetic for several minutes. Slowly insert the applicator into the nares and advance in a line parallel to the zygoma with the tip angled laterally. Do not advance the applicator in a cephalad direction. The endpoint should be the depth marked on the applicator. Place a second applicator into the nare using the same technique, except advance it approximately 0.5–1 cm deeper and superior to the first. If resistance is encountered at any time, slightly withdraw and redirect the applicator. The second applicator is not a necessity and the nares of some patients may not accommodate it. Leave the applicator or applicators in for 30–45 minutes. Signs of a successful block of the SPG include ipsilateral tearing, conjunctival injection, and nasal congestion. If the SPG is a pain generator or transmitter, analgesia should also be apparent. If after 20–30 minutes there are no signs of a block or the patient has not received any pain relief, additional local anesthetic may be needed and can be trickled down the shaft of the applicator. Remove the cotton-tipped applicators after 45 minutes even if there are no signs of block or analgesia, in which case the SPG may be too deep to be blocked by this technique or is not involved in the transmission of pain. Regardless, the infrazygomatic approach should be performed to rule out both of the aforementioned scenarios.
The infrazygomatic approach to SPG blockade is technically challenging. Therefore fluoroscopic guidance is highly recommended, as this will improve the success of the block as well as the speed at which it is performed; it will also decrease potential complications. Noninvasive monitors should be used to record vital signs. Light sedation with midazolam and fentanyl can be used, but on occasion deeper sedation may be necessary for radiofrequency lesioning. For pulsed radiofrequency ablation, heavy sedation is not required.
Place the patient in the supine position. Using sterile procedure, prep and drape the appropriate side of the face. Obtain a lateral fluoroscopic image. Palpate the mandibular notch and anesthetize the skin. If the notch is not palpable, identify the notch on a lateral fluoroscopic view. Identify the pterygopalatine fossa (which appears as a “V”) on the lateral image and superimpose the right and left fossae (see Fig. 82.5 ). This is accomplished by manipulating the C-arm or the head. The block can be performed with a 4.5-inch, 22-gauge short-bevel needle with the distal tip bent at a 30-degree angle or with a curved blunt 10-cm, 20- or 22-gauge needle. The description of the technique reflects the use of a blunt needle. Anesthetize the skin and insert a 1.25-inch 16-gauge angiocatheter through the skin; advance it until it is just medial to the ramus of the mandible. This can be checked on an anteroposterior (AP) image. Pass the block needle through the angiocatheter and advance it medially, anteriorly, and slightly cephalad. Obtain a lateral image to check the direction of the needle. Your target is the middle to upper portion of the pterygopalatine fossa ( Fig. 82.6 ). Get an AP view and advance the needle toward the middle turbinate, stopping when the tip is adjacent to the palatine bone ( Fig. 82.7 ). If resistance is encountered at any point, withdraw and redirect the needle. Given the small size of the fossa, frequent AP and lateral images may be required to redirect the needle. Once in the fossa, inject 0.5–1 mL of nonionic water-soluble contrast and observe for intravascular spread and/or intranasal placement of the needle. Once correct placement has been confirmed, inject 2 mL of local anesthetic with or without steroids.
Radiofrequency and Pulsed Radiofrequency Thermocoagulation
After a successful diagnostic block, two therapeutic choices are available: conventional radiofrequency lesioning (radiofrequency thermocoagulation [RFTC]) and pulsed electromagnetic field radiofrequency (P-EMF) thermocoagulation. An insulated RF needle with a 3- or 5-mm active tip is placed using the infrazygomatic approach. Once in place, sensory stimulation is performed at 50 Hz up to 1 V. If the tip of the needle is adjacent to the SPG, the patient should perceive a paresthesia at the root of the nose at less than 0.3 V. If the paresthesia is felt in the hard palate, the needle should be redirected cephalad and medial. A paresthesia in the upper teeth indicates stimulation of the maxillary nerve, in which case the needle should be placed more caudally and medially. Motor stimulation is not necessary. After appropriate sensory stimulation, RFTC can be performed at 67°C–80°C for 90 seconds times 2 cycles. Before lesioning, 2–3 mL of local anesthetic should be injected. To avoid inadvertent lesioning of other nerves around the SPG, a 3-mm active tip is a better choice. For P-EMF, the size of the active tip is not important, as the electromagnetic field is projected from the tip of the needle and not from the shaft. With P-EMF lesioning, 2–4, 120-second lesions are performed at 45 V. Local anesthetic is not required for P-EMF. The choice of whether to do an RFTC or P-EMF lesioning after a successful block is up to the discretion of the pain practitioner.
Complications include bruising, bleeding, infection, damage to nerves, proptosis from retrobulbar hematoma, dysesthesias, paresthesias, and/or numbness from RFTC. Bradycardia (the Konen reflex) has been noted during RFTC and P-EMF and can be prevented with pretreatment with atropine or glycopyrrolate.