Neurolytic Blocks

Anatomy and Physiology

The anatomy depends on the location of the targeted peripheral nerve or nerve plexus. Careful needle advancement is guided using ultrasonography, fluoroscopy, or nerve stimulation.[6]

Indications

No consensus indications have been established for indications of neurolysis, as targeted nerve destruction can apply to a variety of pain conditions. However, appropriate patient selection is important before interventional pain treatment. Generally, an interventional approach is only considered after conservative treatments have failed. In addition to obtaining a detailed history, performing a thorough physical examination, and conducting a complete diagnostic laboratory workup, a recent radiological evaluation is often necessary to identify the pain's origin and prevent complications associated with the interventional neurolytic technique. A psychological assessment is frequently performed to determine whether the patient is suitable for intervention, especially if a neuromodulatory approach is considered.

Celiac plexus neurolytic blocks are often performed for visceral pain originating from upper abdominal malignancy, especially pancreatic cancer.[7] Superior hypogastric plexus neurolysis may be attempted for patients with pelvic visceral pain.[8] Trigeminal neuropathy may be alleviated with neurolysis of the trigeminal nerve.[9]

Intercostal nerve neurolysis can treat pain from fractured ribs, cancer metastasis, and post-thoracotomy symptoms. Sympathetic plexus neurolysis may also be performed, particularly in patients with cancer pain and neuropathic pain syndromes, including those affecting the thoracic, lumbosacral, and stellate plexuses. This procedure can also address visceral pain related to damage to the sympathetic plexus, such as that treated with celiac, hypogastric, and ganglion impar blocks. Facetogenic and vertebral pain may be alleviated with neurolysis of the medial branch of the primary dorsal ramus. Neuraxial administration of alcohol and phenol has fallen out of favor due to significant adverse effects and is typically described in spasticity disorders and the end-stage cancer population.[10][11]

Contraindications

Absolute contraindications to targeted neurolysis include patient refusal, active infection at the site of injection, and allergy to a chemical neurolytic agent. Bleeding disorders or anticoagulation treatment are also considered contraindications, particularly if injection occurs at noncompressible sites. The proceduralist should consult pacemaker interrogation services if a pacemaker is in place and radiofrequency ablation is planned.

Equipment

The necessary equipment for a neurolytic block typically includes the following:

• Chlorhexidine gluconate or povidone-iodine
• Ultrasound probe with a sterile probe cover and gel, if applicable
• Fluoroscopy equipment, if applicable
• Nerve stimulator, if applicable
• Local anesthetic, typically 1% lidocaine, for superficial layer local anesthesia
• Regional block local anesthetic test solution, such as 2% lidocaine or 1.5% mepivacaine
• A 10- to 20-mL syringe with extension tubing
• Block needle (length varies based on the depth of the targeted peripheral nerve) or, for the neuraxial approach, a spinal or epidural needle (needle characteristics are based on body habitus and clinician's preference)
• Chemical neurolytic agents, such as alcohol and phenol, if applicable
• Radiofrequency probe, if applicable
• Cryomachine and cryoprobe with cooling agents, such as nitrous oxide and carbon dioxide, if applicable

Agents used for chemical neurolysis primarily include 50% to 100% alcohol and 5% to 15% phenol. However, other agents, such as hypertonic saline, glycerol, ammonium salt solutions, and chlorocresol, have also been described.[12] The mechanism of action for alcohol neurolysis is axonal and Schwann cell destruction from phospholipid extraction in the cell membrane and lipoprotein precipitation.[13] Phenol infiltration causes damage from protein coagulation and degeneration.[14]

Radiofrequency probes are commonly used for medial branch nerve ablation, percutaneous cordotomy, Gasserian ganglion thermocoagulation, percutaneous rhizotomy, and percutaneous radiofrequency sympathectomy. Conventional radiofrequency ablation generates a current with an oscillating frequency, producing heat that creates circumscript lesions used for selective nerve lesioning. Generally, heat at temperatures greater than 60 °C is used to create lesions. Pulsed radiofrequency ablation is similar to conventional thermal ablation, although it uses a higher voltage in a pulsatile manner, permitting energy to dissipate easier and generating less heat. Cooled radiofrequency ablation involves active cooling with a continuous flow of water that prevents the current from reaching high temperatures experienced in conventional ablation. This approach allows for higher temperatures and more spherical and larger lesioning.

Cryoprobes attached to a cryomachine can target nerves by exposing them to frigid temperatures. Cryoablation disrupts the vasa nervorum, leading to axonal destruction. The procedure may also be associated with a decreased incidence of postprocedural hyperalgesia and the formation of neuromas when compared to conventional radiofrequency ablation.[15]

Finally, surgical neurolysis or neurectomy involves directly severing a nerve and is generally reserved for rare cases with a poor prognosis. This modality carries a high risk of deafferentation pain, a complication due to loss of neuronal input leading to spontaneous firing within the spinothalamic tract.[16] This pain may become more severe than the original symptoms present before neurolysis.

Personnel

A pain medicine specialist trained in ultrasound- and fluoroscopy-guided nerve injections is preferred for performing neurolysis. Additional support from nursing staff trained in sedation anesthesia can assist the clinician during the procedure, ensuring patient safety and comfort.

Preparation

The proceduralist should obtain informed consent before the procedure. The patient is positioned appropriately depending on the location of the targeted nerve. Minimal or no sedation is typically required. However, moderate sedation may be considered in certain instances, such as during chemical neurolysis with alcohol, which may be painful, or radiofrequency ablation. The aseptic technique should be maintained throughout the procedure.

Technique or Treatment

Under aseptic conditions, the target nerve is identified using fluoroscopy, ultrasound, or nerve stimulation. The skin is infiltrated with a local anesthetic. The needle, radiofrequency probe, or cryoprobe is advanced toward the target nerve. After a preliminary aspiration, a diagnostic block with a local anesthetic may be performed to confirm the position. Subsequently, neurolysis—such as through alcohol or phenol injection and radiofrequency ablation—may be accomplished. Diagnostic blocks are typically performed before neurolytic intervention to allow better prediction of efficacy. Cardiovascular monitoring with resuscitative backup should be readily available. Patients should be counseled that the therapeutic effects of neurolysis, particularly chemical neurolysis, may not be evident for 3 to 7 days (see Image. Neurolytic Celiac Plexus Block, Radiograph).

Complications

As with any interventional procedure, complications such as bleeding, infection, pain, and damage to surrounding tissue may occur. Intravascular injection of a neurolytic agent may result in systemic toxicity, depending on the chemical agent used. Superficial cryoablation may lead to skin damage, manifesting with alopecia, hypopigmentation, or hyperpigmentation.[17] In rare cases, neuritis may develop following partial denervation with a neurolytic agent, potentially resulting in nerve regeneration and hyperesthesia that could be more severe than the original pain.[18] If a motor nerve undergoes neurolysis, it may lead to prolonged motor paralysis. In addition, denervation can lead to bowel, bladder, and sexual dysfunction.

Clinical Significance

A neurolytic block involves the targeted destruction of a nerve or nerve plexus. Chemical, radiofrequency ablation, cryoablation, and neurosurgical procedures are commonly performed with fluoroscopy to improve the precision and efficiency of targeted neurolysis. Patients often receive substantial reductions in pain.

Enhancing Healthcare Team Outcomes

Various case series, observational trials, and randomized controlled trials have investigated the outcomes of neurolysis. However, large data pools have not been collected due to the heterogeneity of nerve targets and the wide variety of tools used for this procedure. For chemical-based procedures, phenol neurolysis may provide therapeutic relief for 8 to 12 weeks, whereas alcohol neurolysis generally lasts 12 to 24 weeks. Radiofrequency ablation of peripheral nerves may last 3 to 12 months until axons regenerate.[19] Cryoanalgesia may provide variable relief, lasting weeks to months.

Of studies regarding chemical neurolysis, those targeting the celiac plexus for pancreatic malignancy have been extensively described. A meta-analysis demonstrated that neurolytic celiac plexus block in patients with unresectable pancreatic cancer was associated with improved pain scores, reduced opioid use, and decreased constipation.[20]

Of nonchemical interventional approaches to the neurolysis of peripheral nerve targets, radiofrequency ablation of the medial branch of the dorsal primary rami, which innervates facet joints, has been most studied. A prospective 10-year clinical trial investigating radiofrequency neurotomy of the lumbar facet joints for relief of chronic low back pain showed that more than 68% of patients reported good (greater than 50%) to excellent (greater than 80%) pain relief lasting 6 to 24 months.[21] Furthermore, Lee et al performed a meta-analysis of randomized controlled trials comparing the efficacy of conventional radiofrequency ablation with control treatment (sham or epidural block). This study showed a more significant improvement in back pain scores in the radiofrequency ablation group at a 1-year follow-up.[22]

Research has also compared the efficacy of radiofrequency ablation to that of chemical neurolysis. A randomized controlled trial evaluating radiofrequency ablation versus chemical neurolysis of thoracic splanchnic nerves for abdominal malignancy pain demonstrated that radiofrequency ablation of the splanchnic nerves at the T10 and T11 levels is more effective than alcohol neurolysis alone. Patients in the radiofrequency ablation arm also reported faster and longer-acting duration of analgesia with a better safety profile.[23] Factors associated with a poor response to radiofrequency facet denervation include long duration of pain, previous back surgery, depression, and the number of treated joints.[24][25]

Despite these meta-analyzed data, controversy still exists regarding the long-term efficacy of radiofrequency ablation for low back pain.[26][27] For example, a recent study involving 3 separate randomized controlled trials conducted by Juch et al included patients with chronic low back pain from conditions of the facet and sacroiliac joints or intervertebral disks. The group reported that radiofrequency ablation combined with exercise compared to exercise alone resulted in no difference in pain intensity after 3 months.[28]

A systematic review of the efficacy of cryoablation in the cancer pain population demonstrated that cryoablation decreased pain scores by more than 60% at 24 hours post-procedure, by 70% at 3 months, and by more than 80% at 6 months.[29] Furthermore, cryoablation was associated with about a 44% and 60% improvement in the quality of life at 4 weeks and 8 weeks post-procedure, respectively. The need for opioids also decreased significantly by about 60% at 3 months. 

Data on surgical neurectomy are even more limited, typically involving peripheral nerves at the trunk. A study investigating neurectomies of the ilioinguinal, iliohypogastric, genitofemoral, lateral femoral cutaneous, and intercostal nerves demonstrated that this modality is reasonable for the treatment of chronic postoperative neurogenic pain, leading to significant improvement in pain scores and quality of life.[30]

Of all peripheral nerve neurectomies, ilioinguinal and iliohypogastric neurectomies have been most extensively studied, primarily in patients with post-herniorrhaphy inguinal neuralgia. A tailored neurectomy approach of the ilioinguinal and iliohypogastric nerves can be 3 times more effective than tender point infiltration in alleviating chronic inguinodynia after anterior hernia mesh repair.[31] Several randomized controlled trials intervening with prophylactic planned ilioinguinal neurectomy at the time of inguinal hernia repair have also been reported to lead to a decrease in the incidence of chronic postoperative pain.[32]

Outcomes data on neurolysis for pain relief remain inconsistent due to variable patient selection, diagnostic criteria, type of intervention, and outcome measures. Due to the absence of compelling evidence and the lack of data suggesting low-risk, long-term benefits, neurolysis should be cautiously considered only after a failure of other modalities, including pharmacologic, physical, psychiatric, and nondestructive interventional therapies.