Introduction
The human body’s nervous system is broken into the central and peripheral nervous systems. The peripheral nervous system is further subdivided into the somatic nervous system, which controls skeletal muscle and dictates the body’s movement, and the autonomic nervous system. The autonomic nervous system is even further subdivided into the parasympathetic and sympathetic divisions. The sympathetic nervous system (SNS) and pain have an intricate relationship in which the SNS functions as one of the body’s protective mechanisms against stressful stimuli through the use of bidirectional interactions for the central processing of pain. Cortical pain and descending inhibition of pain may be partly controlled through SNS activation. ,
When SNS blockage does not relieve a person’s pain, it is defined as sympathetically independent pain (SIP). Pain that is relieved by specific sympatholytic procedures is called sympathetically maintained pain (SMP). SMP is a symptom of various neuropathic pain conditions. These different pain syndromes include abdominal cancer pain, complex region pain syndrome (CRPS) or reflex sympathetic dystrophy (RSD), cluster headache, and many other pain syndromes. SMP is most commonly found in complex regional pain syndrome type 1 (CRPS 1). The incidence of CRPS is estimated to be 26.2 per 100,000 person years with females being affected at least three times more often than males. Pain originating from visceral, vascular, neuronal, and musculoskeletal entities all seem to have their signals propagated by the SNS. , Thus, treatments for pain syndromes that can be attributed to these entities are often targeted at the sympathetic nerves and ganglion that conduct the nociceptive signals causing patients pain.
Treatment of SMP is important due to the large toll it takes on a patient’s life. In particular, CRPS or RSD of the upper extremity has a great effect on daily life, with many patients being limited in activities of daily living (ADL). A study looking into the health-related quality of life in patients with CRPS 1 found patients with CRPS 1 are mainly burdened by the physical consequences of the syndrome. This study also found that bodily pain and vitality were significantly related to age. More generally, pain syndromes with SMP can affect not only physical health, but also a patient’s psychological well-being, their work, and their relationships.
Stellate ganglion blockades (SGBs) are used in the treatment of CRPS and other medical conditions. Not only are SGBs used for this, they are also used as a diagnostic tool to confirm if a patient’s pain is SMP. , Diagnostic nerve blocks are used to correctly identify which nerve is causing someone’s pain before more permanent or invasive procedures are performed. When treating SMP there are more targets than the stellate ganglion. Other targets include thoracic or lumbar ganglia, the celiac plexus, splanchnic nerves, sphenopalatine ganglion, the superior hypogastric plexuses, and ganglion impar, even though some of these are not purely sympathetic fibers. ,
Pharmacotherapies and conservative management are typically tried and failed before pursuing interventional procedures in the field of pain management. Once a specific nerve is determined to be the cause of a patient’s pain from one or more diagnostic nerve blocks, a neurolytic procedure such as radiofrequency ablation (RFA) or pulsed radiofrequency (PRF) can be prolonged to increase the duration of relief. When patients with refractory pain are correctly selected to undergo these procedures, they have shown to have great promise. , , Due to the great potential of the use of RFA and PRF in the treatment of SMP, we discuss the procedures in the following sections of this chapter. Specifically, we address anatomical considerations, procedure details, potential complications, and chronic pain conditions that could require the treatment.
Anatomic considerations
There are two primary divisions of the autonomic nervous system (ANS) that are represented within the peripheral nerves: sympathetic and parasympathetic divisions. Neuronal bodies of the ANS originate from the gray matter of the lateral horn of the spinal cord. Sympathetic nerve axons exit the spinal cord via the ventral root between the levels of T1 and L2 and typically terminate abruptly at prevertebral ganglia located just outside of the spinal cord, where they synapse with postganglionic cell bodies. Postganglionic cell bodies, which are often the targets of RFA procedures, can be separated into paravertebral fibers, located within the sympathetic chain which runs parallel to the vertebral column, and prevertebral fibers, which run along the abdominal aorta and ventral branches. These fibers spread across the body, carrying sympathetic signals to tissue. Common sympathetic targets of RFA procedures include the thoracic splanchnic nerves, celiac plexus, ganglion impar, sphenopalatine ganglion, and stellate ganglion. Each of these targets offers a different therapeutic benefit for patients based on the type of pain they experience and the physiology underlying that pain. Often, the physiology of a patient’s pain is poorly understood, and clinicians must follow a series of steps, including conservative management, diagnostic nerve blocks, and ultimately more invasive procedures, such as RFA, to address these pain syndromes.
The most superior sympathetic target for RFA procedures is the trigeminal ganglion. Pain, light touch and temperature sensation from the skin of the face, nasal and oral mucosa, teeth and the anterior two thirds of the tongue are supplied through somatic afferent fibers. Tensor tympani, muscles of mastication, and muscles of facial expression are supplied through visceral different fibers. The trigeminal ganglion communicates with the autonomic nervous system through the ciliary, sphenopalatine, otic, and submaxillary ganglion ( Fig. 16.1 ) to trigeminal neuralgia and its varied subtypes.
Next to the trigeminal ganglion is the sphenopalatine ganglion, which receives sympathetic input from postganglionic fibers which originate from the cervical level. The sphenopalatine ganglion can be found deep to the pterygoid fossa at the opening of the pterygoid canal, just posterior to the maxillary sinus. Therapies which target the sphenopalatine ganglion, such as RFA, are typically directed at treating the following conditions: cluster headache, second-division trigeminal neuralgia, and migraine headaches. There are three cervical ganglia, all of which are prevertebral ganglia, which form when preganglionic fibers pass through paravertebral ganglia without synapsing ( Fig. 16.1 ). The stellate ganglion is the most inferior cervical ganglion and is typically formed by a fusion of the ganglia at C7 and T1 levels. , The stellate ganglion lies anterior to the transverse processes of the vertebrae, anteromedial to the vertebral artery, and medial to the common carotid artery and jugular vein. Therapies which target the stellate ganglion can be used to manage a wide array of conditions, including complex regional pain syndrome, chronic postsurgical pain, Raynaud disease, orofacial pain, atypical chest pain, and many others.
The thoracic splanchnic nerves, which include the greater, lesser, and least splanchnic nerves, can be found across the thoracic spinal levels. These represent preganglionic fibers which pass through paravertebral ganglia and do not synapse, but instead give rise to the nerve fibers which extend across the chest and abdominal cavities ( Fig. 16.2 ). The greater splanchnic nerve originates from the T5–T6 or T9–T10 levels, the lesser splanchnic nerve originates from the T9–T10 or T10–T11 levels, and the least splanchnic nerve originates from the T11–T12 levels. , From their origins, these nerves synapse with the celiac plexus, which is a prevertebral ganglia that surrounds the celiac and superior mesenteric arteries at the point at which they branch from the abdominal aorta. , Along with the local vasculature, the pancreas lies anterior to the plexus, and the inferior vena cava runs along the right border of the plexus. Therapies that target the thoracic splanchnic nerves and celiac plexus are typically directed at treating refractory, visceral abdominal pain and pain related to malignancies involving organs of the upper abdomen, including the pancreas, biliary tree, and retroperitoneal organs ( Fig. 16.3 ). ,
The paravertebral lumbar sympathetic ganglia ( Fig. 16.4 ) run anterolaterally to the lumbar vertebrae within the peritoneal cavity, with the abdominal aorta and inferior vena cava located anteriorly. Somatic nerves also lie in close proximity to the lumbar sympathetic ganglia, which is relevant to consider when targeting these regions with RFA, as irreparable damage to the local somatic nerves might severely impact a patient’s daily function and quality of life. , An ipsilateral oblique approach is demonstrated in Figs. 16.5 to 16.7 . Preganglionic fibers in this region may synapse in the sympathetic chain or travel directly to the lumbar splanchnic nerves, which ultimately target the abdominal aortic, inferior mesenteric, and hypogastric plexuses. Treatments targeting the lumbar sympathetic ganglia and lumbar splanchnic nerves are aimed at treating a variety of conditions, such as complex regional pain syndrome, lower limb painful ischemia, phantom limb pain, neuropathic pain, hyperhidrosis, Raynaud disease, and pain related to malignancy. The use of RFA to modulate pain associated with these conditions is typically reserved for instances where the pain is refractory to conservative methods but improved with diagnostic nerve block. RFA needles can be placed using a similar oblique approach to target the lumbar sympathetic chain ( Fig. 16.8 ) and a transdiscal approach for the superior hypogastric plexus ( Fig. 16.9 ).
The most inferior target of sympathetic RFA procedures is the ganglion impar, which is formed with the fusion of the right and left sympathetic chains and lies anterior to the sacrococcygeal junction and posterior to the rectum. , The ganglion impar helps provide innervation to pelvic viscera and genitalia, thus, treatments that target the ganglion impar address pain conditions like coccydynia as well as nonspecific, anorectal, perineal, and genital pain. ,
Procedure details
Radiofrequency (RF) is a type of energy that is performed to create heat and obtain tissue necrosis. Alternating high-frequency current is used in RF procedures to change nociceptive pathways. There are two types of radiofrequency treatments including conventional RF (CRF) and pulsed RF (PRF).
CRF is used to produce a thermal lesion in a specific nerve with RF current; this lesion causes an interruption of nociceptive pathways. This thermal lesion is produced specifically through the use of an alternating current in the frequency range of 100–500 kHz applied continuously. The thermal lesion generated in a nerve to block pain transduction is best obtained when the electrode temperature is heated to 65–75ºC, to induce coagulation, for 60 to 90 s.
PRF allows for a current to be delivered without heating the nerve to a level that risks causing a histologic lesion. , PRF is performed by delivering a 50,000 Hz current in 20-millisecond pulses at a frequency of two per second; this use of bursts of delivery allows for heat dissipation and does not allow for thermal lesions. , To aid in limiting heating of the nerve’s tissue, the electrode tip is kept to a temperature below 42ºC. There is a temporary block of conduction along a nerve that was heated to a low temperature (40–45ºC), however, it is indicated there is no physiologic lesion generated due to the rapid recovery of function.
Complications
While complications from RFA procedures are quite rare, there remains a risk of both mild and serious complications from the procedure, including infection, bleeding, neurogenic complications, puncture-related pain, nerve injury, pneumothorax, brain damage, and death. In order to minimize the risk of serious complications, clinicians should be meticulous in their patient selection, be well versed in the local anatomy related to the procedure, and utilize image guidance throughout the procedure. Fluoroscopy, ultrasound, and computed tomography (CT) are all commonly used in RFA procedures to guide needle and RF cannula placement and to help clinicians avoid damaging regional structures. These options are most commonly utilized in procedures targeting the stellate ganglion, while endoscopic ultrasound and endovascular approaches have been shown to be more useful in procedures aimed towards the celiac plexus. Additionally, complications are more common in CRF procedures than in PRF procedures due to the greater temperatures reached in CRF, resulting in more tissue damage and a greater likelihood of injury. PRF should be favored in situations where it is equally effective as CRF in offering pain relief, as it likely offers advantages in safety by preventing a destructive build-up of heat.
Puncture-related pain, bleeding, and infection are typical complications that often result from the introduction of the RF cannula and needle placement during the procedure. Puncture-related pain is the mildest of these complications. It is typically limited to the injection site and resolves quickly. Infections have been documented in RFA procedures targeting the ganglion impar; however, it is unlikely that risk of infection fully dissipates when RFA procedures are directed towards other sympathetic nervous system targets. Patient bleeding during or immediately following RFA procedures varies widely in severity, ranging from local bleeds to hematoma at the puncture sites. , ,
Neurogenic complications from RFA procedures can be both painful and nonpainful. Neuropathic pain syndromes reported following RFA interventions include postsympathectomy neuralgia, parasthesia, and regional pain. , , Nonpainful complications include hypoesthesia, Horner’s syndrome, ptosis, and off-target nerve lesions. It is relevant to note that patients who experienced Horner’s syndrome and ptosis following RFA all underwent RFA targeting the stellate ganglion. Unlike infection risk, it is likely that the risk of experiencing Horner’s syndrome and ptosis as complications of RFA is unique to procedures geared toward ablating the stellate ganglion. , Systemic complications of RFA procedures include vasovagal collapse, hypotension, abdominal colic, and diarrhea. These systemic complications are highly dependent on the targets of the RFA procedure. Clinicians should discuss the possible complications with patients based on the sympathetic nervous system targets in question, to allow patients to remain vigilant of these symptoms. Vasovagal collapse has been specifically documented in CRF procedures targeting the stellate ganglion. Hypotension, abdominal colic, and diarrhea have been reported in CRF procedures targeting the splanchnic nerves. , Hypotension has also been reported in CRF procedures targeting the lumbar sympathetic ganglia; however, the hypotension experienced by these patients was temporary and the CRF procedure was conducted in combination with chemical neurolysis, which may have further complicated the patients’ risk of experiencing the symptoms. In order to best avoid complications, clinicians should only proceed with RFA procedures in patients who report a type of pain consistent with neuralgias shown to be treated effectively with RFA, have pain refractory to conservative management, and whose pain is successfully relieved from a diagnostic nerve block at the intended target site. , , Additionally, a comprehensive understanding of the regional anatomy of the nerve target is critical for clinicians to avoid implicating local structures that may further increase a patient’s risk of infection, bleeding, or long-term damage.
Chronic pain conditions
There is a large variety of sympathetic pain conditions that have been shown to be effectively treated with RFA procedures. Given that the underlying causes of these pain conditions vary greatly in anatomic location and physiology, the targets of RFA procedures to treat these conditions are highly dependent on patient symptoms, clinical criteria, and procedural steps, such as diagnostic nerve blocks, to confirm that the patient’s pain is being accurately attributed to the intended target of the RFA procedure. Some of the most common sympathetic pain conditions that are treated with RFA procedures include coccydynia, headaches, facial pain, abdominal pain, neuropathic pain syndromes, such as postmastectomy pain, complex regional pain syndrome (CRPS), phantom pain, and lower extremity pain related to diabetic peripheral neuropathy
There are many pain syndromes that may underlie perineal pain, including coccydynia, vulvodynia, rectal pain, and others. Coccydynia, defined as localized pain to the tailbone or coccyx superior to the anus, has been extensively studied as a candidate for RFA treatment. Typically, this pain occurs in the absence of low back pain or other pain that refers to the coccyx and is most commonly the result of prior trauma, though it can develop idiopathically. Conservative treatment options include changes to daily life, such as a modified sitting position, nonsteroidal antiinflammatory drugs (NSAIDs), and physiotherapy. , As previously discussed, the ganglion impar is a common target for procedures intended to improve pain secondary to coccydynia and other perineal pain syndromes. Fig. 16.10 shows an RF needle targeting the ganglion impar using a transcoccygeal approach. CRF targeting the ganglion impar has been shown to offer patients suffering from coccydynia and other types of perineal pain long-term pain relief. , While the current evidence indicates that CRF offers more effective pain relief for these conditions compared to PRF, there have been studies conducted which found PRF offers significant pain relief to patients compared to nerve blocks. , There is also growing evidence to indicate that CRF to the ganglion impar can be used to effectively relieve pain related to colon cancer malignancy and constant anal pain. ,
