Indications
Diagnostic sympathetic blocks are used to confirm the presence of sympathetically mediated pain. Longer-acting therapeutic blocks can be performed by injecting neurolytic substances or repeated local anesthetic administrations. Physical modalities, such as radiofrequency denervation or cryoneurolysis of sympathetic nerves, may be utilized.
Sympathetic blocks are used to treat visceral, vascular, and neuropathic pain.
Visceral Pain
A). Foregut and midgut structures (stomach, duodenum, pancreas, biliary system and liver, small intestine) are innervated by the celiac plexus. Blocking this plexus may relieve pain and nausea, often associated with malignancies of the above-mentioned organs. If successful, this procedure may significantly reduce or even eliminate the need for opioid therapy. If a neurolytic agent is used, the relief may last from weeks to months.[9] Celiac plexus blocks and/or neurolysis may be repeated if symptoms recur, though the duration of pain relief may diminish with repeated neurolysis.[10]
B). Hindgut structures (descending, sigmoid colon, and proximal rectum) and pelvic organs (uterus, ovaries, prostate, urinary bladder, testes, and seminal vesicles) are innervated by the superior hypogastric plexus. A blockade of this prevertebral ganglion may be used to treat persistent or intractable pelvic and rectal pain that failed conservative treatment measures.[11]
C). Inferior hypogastric plexus block may be utilized to treat pelvic, perineal, and genital pain of benign or malignant etiology. This procedure is not commonly used due to the pre-sacral location of the ganglion, posing difficulty to access and a higher risk of complications.[12]
D). Distal structures of the pelvis are innervated sympathetically by the ganglion Impar. This ganglion may be blocked to treat malignant vulvar, rectal and anal pain, intractable sacral and perineal pain (e.g., postherpetic neuralgia), and/or coccydynia.[13]
E). The thoracic paravertebral sympathetic chain not only transmits nociceptive input from the thoracic viscera but also acts as a relay station for white rami traveling to the cervical, abdominal, lumbar, and sacrococcygeal sympathetic nodes. Due to proximity to somatic nerves and complex surrounding anatomy,[14] the thoracic paravertebral sympathetic chain is very rarely blocked, as the effect is often difficult to predict. Furthermore, the anatomy poses a higher risk of a somatic block and other complications.
If the primary disease process involves somatic structures (e.g., malignancy invading abdominal walls or musculoskeletal tissues, nerves), and the pain gains a somatic component, a sympathetic block may be less efficacious. In such cases, regional and neuraxial techniques may improve the quality of pain relief. Neuraxial analgesia (intrathecal or epidural) will block somatic and visceral afferents simultaneously, which is the basis for the implantation of long-term intrathecal drug delivery systems.
Neuropathic Pain
Sympathetic blocks can provide significant, yet often incomplete relief of neuropathic pain and are usually combined with adjuvant therapies (e.g., physiotherapy, medications, and/or neuromodulation). The role of sympathetic blocks in treating acute herpes zoster pain remains unclear. Pain from herpes zoster of the trigeminal region may be treated with stellate ganglion blocks, which may decrease the risk of developing postherpetic neuralgia.[15][16] Allodynia and pain from herpes zoster of the trunk and extremities may be relieved better with epidural or paravertebral injections with local anesthetics and corticosteroids.[17][18][19] The efficacy of sympathetic blocks for the treatment of postherpetic neuralgia remains controversial.[20][21] Only one case report suggests lumbar sympathetic block may be efficacious in the treatment of refractory painful diabetic neuropathy.[22] Phantom limb pain is hypothesized to be partially sympathetically mediated and pathophysiologically similar to complex regional pain syndrome type II. A recent case series and a pilot study suggest sympathetic blocks may be effective in providing pain relief for stump pain. Yet, due to a limited amount of evidence, the role of sympathetic blocks in phantom limb pain remains unclear.[23][24]
Ultimately, sympathetic nerve blocks are not indicated for chronic treatment of neuropathic pain not related to CRPS according to the practice guidelines from the American Society of Anesthesiologists Task Force of Chronic Pain Management and the American Society of Regional Anesthesia and Pain Medicine.[25] The sympathetic blockade has proven to be beneficial in the treatment of complex regional pain syndrome (CRPS). In part, the pathogenesis of CRPS stems from the emerging hypersensitivity of nociceptors to norepinephrine released from sympathetic efferents and loss of the SANS’s inhibitory influence on pain.[26] Such sympathetically maintained pain is present in one-third of patients with CRPS.[27] In this condition, the effects of diagnostic sympathetic blockade may be prolonged and therapeutic, aiding in the rehabilitation of patients. Both stellate ganglion (for upper extremity CRPS) and lumbar sympathetic blocks (for lower extremity CRPS) with local anesthetics and adjuvants (i.e., clonidine, steroids) offer benefit and are indicated when conservative, non-invasive treatments fail.[24][28] Neurolysis or ablation of the lumbar plexus is possible and may provide a longer-lasting relief in patients with short-lived, but adequate relief from sympathetic blocks.[29]
Vascular Pain
Pain from tissue ischemia (e.g., vasospastic, thrombotic, embolic) is transmitted via sympathetic afferent fibers and is enhanced by sympathetic vasoconstriction. Simultaneously, chronic ischemia can result in direct damage to soft tissues (e.g., ulceration) and nerves, adding somatic and neuropathic nociceptive components, respectively. Lumbar sympathetic block for treatment of resting pain of obliterative lower extremity disease (e.g., thromboangiitis obliterans and atherosclerosis) was historically among the most beneficial neural percutaneous interventions available with the majority of patients responding with a significant decrease in pain and increase in perfusion in the affected extremity.[30] Neural ablation or denervation of the lumbar chain in these patients facilitates exercise and rehabilitation, leading to lasting improvement.[31] Pain from chronic vasospastic disease (e.g., Raynaud syndrome, acrocyanosis, livedo reticularis, sequelae of poliomyelitis, and spinal cord injury) and cold injury are quite responsive to sympathetic blocks as well.[32][33]
Hyperhidrosis
Sympathetic ganglion blocks can provide temporary relief of hyperhidrosis.[34] Surgical ganglionectomy was widely used to treat this condition; however, due to a high incidence of post-sympathectomy pain (11%),[35] this surgery is not employed. Chemical block and, if possible, lysis/ablation provides a safer alternative.[34]
Acute Treatment of Electrical Storm
A severe form of recurrent sustained ventricular tachycardia with greater than or equal to 3 episodes in 24 hours is called an electrical storm. It is associated with a 2-fold to 8-fold increased risk of sudden cardiac death. A recent prospective study[36] and several case studies reported up to 90% efficiency of left-sided or bilateral stellate ganglion blocks in decreasing ventricular arrhythmia burden.
Post-traumatic Stress Disorder (PTSD) Treatment
A recent randomized control trial showed the efficacy of stellate ganglion blocks in the treatment of PTSD.[37] It is hypothesized that the right-sided stellate ganglion blockade may locally decrease the nerve growth factor level, leading to a reduction or even reversal of the sympathetic nerve sprouting in the plexus and among its anatomic connections. This, in turn, results in the reduction of cerebral norepinephrine levels. The block also directly interrupts signaling from the stellate ganglion to the amygdala – the brain region responsible for processing emotions such as anxiety and fear. Both of these actions reduce the symptoms of PTSD, with the effect lasting from weeks to months.[38][39]
Evidence of Blockade
Common subjective signs of sympathectomy include pain relief, warmth, decrease in perspiration, and change in color of the area supplied by the nerves blocked. Objective tests are recommended and include measuring skin temperature (which is expected to elevate for the ipsilateral limb as compared to the contralateral limb) and blood flow, skin conductance, and provocative sweat tests (e.g., cobalt blue or ninhydrin sweat tests).[40] Horner triad (ipsilateral partial ptosis, myosis, and facial anhydrosis) is a sign of sympathectomy at the inferior cervical (stellate) ganglion level. Yet, it does not always correlate with effective pain relief of the upper extremity. Note that the upper extremity receives some of its sympathetic efferents from the upper thoracic ganglia, which may not be reached by the anesthetic from the stellate ganglion block.[41]
Technique or Treatment
Stellate Ganglion Block[42][43]
Specific Indications
Sympathetically maintained pain of upper extremities and upper thoracic area (including CRPS types I and II); post-radiation neuritis; vasospastic conditions (Raynaud syndrome) and vascular insufficiency, vasculitis, arterial embolism of the face or upper extremities; pain from acute herpes zoster of upper extremities and neck; post-traumatic stress disorder; acute treatment of electrical storm (sustained ventricular tachyarrhythmias); hyperhidrosis.
Technique
The stellate ganglion is formed by the fusion of the inferior cervical ganglion with the first thoracic ganglion bilaterally in about 80% of the population. However, if they are not connected, then the first thoracic ganglion is considered the stellate ganglion. The stellate ganglion is located anterior to the C7 transverse process and the base of the first rib on the anterior aspect of the longus colli muscle under the prevertebral fascia, posterior to the vertebral vessels, lateral to the trachea, and medial to the jugular vein and common carotid artery. Despite its location at the level of C7, the stellate ganglion block is typically performed at the level of C6 because there is a lower risk of pneumothorax and vertebral artery puncture (note that C6 is the most inferior level at which the vertebral artery lies within the transverse foramen, whereas the vertebral artery lies anterior to the C7 transverse foramen).
The stellate ganglion block may be performed using an anterior, posterior, or vertebral body approach.[44][45] Using the anterior approach, the patient is positioned supine, with the neck slightly extended. Patients should be monitored with pulse oximetry, continuous electrocardiogram (ECG)/telemetry, and blood pressure manometry throughout the procedure. This block may be performed using landmarks, ultrasound, or CT guidance, however, it is most commonly performed under fluoroscopic guidance.
Under fluoroscopy, an anteroposterior (AP) view of the cervical spine is acquired, and the C6 vertebral body is located. The carotid artery should be identified by either palpation or ultrasound and may be retracted laterally to avoid puncture during needle placement. The needle is then advanced to target the Chassaignac tubercle (the anterior tubercle of the C6 transverse process) until contact with bone occurs; then, the needle should be withdrawn very slightly (1 mm to 2 mm) to lie just anterior to the longus colli muscle. After negative aspiration, 1 mL to 2 mL of contrast is injected to visualize appropriate spread superior and inferior to the injection site. Given negative aspiration and test-dose (0.5 mL of a local anesthetic), 3 mL to 10 mL of local anesthetic with or without corticosteroid is injected in the area of the ganglion. If the patient meets the criteria for discharge, he/she can leave the recovery room 30 to 60 minutes after the procedure with an escort.
Complications and Side-effects
Horner syndrome, impaired vision, and stuffy nose on the side of injection are very common. The anesthetic may spread to brachial plexus (causing temporary paresthesia, motor, and sensory deficits), recurrent laryngeal nerve (causing temporary hoarseness, an altered sensation of swallowing, and rarely, dyspnea), and phrenic nerve (causing respiratory compromise in patients with preexisting lung disease). Accidental intrathecal, subdural, or epidural injection may result in total spinal anesthesia. Neuraxial damage is also possible and may result in neurologic impairment and even paralysis. Vascular air embolism, pneumocephalus, perforation of trachea/esophagus, chylothorax, or pneumothorax are rare, yet possible. Intravascular injection (most common in the vertebral artery) can cause immediate onset of seizures. Given the close proximity to many vascular structures, there is also always a risk of local anesthetic systemic toxicity, damage to any surrounding vessels, bleeding, and/or hematoma.
Splanchnic Nerve Block[46]
Specific Indication
Upper abdominal and retroperitoneal pain secondary to malignancy (tumors of the lower third of the esophagus, stomach, duodenal, pancreatic cancer, and cancer of the biliary tract). A splanchnic nerve block is used as an alternative to celiac plexus block in situations where there is pre-aortic adenopathy, significant scarring, or tumor burden in the area of celiac trunk origin, posing risk or difficulty of guiding the needle to the celiac plexus. The procedure may also be considered if the original celiac plexus block was unsuccessful. Being performed intimately close to the pleural cavity and somatic nerve roots, it carries a higher risk of pneumothorax and collateral somatic nerve damage, respectively, which limits its use.
Technique
The three separate splanchnic nerves – the greatest (originating at T5-T9 segments of the spinal cord), the lesser (T10-T11), and the lowest (T12), descend down the anterior surface of thoracic vertebral bodies, traversing the diaphragm through crura and forming the celiac plexus. Since all the visceral sensory nerves that pass through celiac ganglion continue to splanchnic nerves, blocking the last will carry virtually undistinguishable effects and complications, yet targeting an alternative anatomic location. The technique of this block is very similar to transcrural celiac plexus block, the difference being the actual retrocrural position of the needle tips and injectate, as well as a higher vertebral level of needle placement.
All patients must be appropriately monitored during the procedure (electrocardiography, noninvasive blood pressure, and pulse oximetry). Intravenous access and availability of crystalloid solutions for infusion are strongly recommended in anticipation of hypotension. The patient is placed in a prone position with a pillow under the abdomen. A skin is marked and anesthetized on both sides, 7 cm to 8 cm lateral to L1 vertebral midline below the 12th rib. A needle is inserted at the marked point and advanced toward the anterolateral border of the T12 vertebral body under fluoroscopic guidance. On a lateral view, needles should project on top of the anterior surface of the T12 body at its superior portion. A contrast should spread in cephalocaudal directions along the anterolateral vertebral body surfaces. Given negative aspiration, a test dose of 3 mL to 5 mL of diagnostic or neurolytic (ethanol, phenol) solution should then be injected. If no sign of motor or somatic sensory block occurs after about 5 minutes, the remaining 10 mL to 15 mL of the solution may be administered.
Complications and Side-effects
Complications of splanchnic nerve block are identical to those of celiac plexus block (see below), with the exception of higher risk of pneumothorax and somatic nerve injury, due to close proximity of pleura and nerve roots.[47]
Celiac Plexus Block[48][49]
Specific Indications
Chronic intractable pain (mostly malignant) of foregut and midgut structures - stomach, duodenum, pancreas, biliary system and liver, small intestine.
Technique
Celiac plexus varies anatomically between patients, but is typically composed of one to five anatomically distinct ganglia (celiac, aortic, renal, and superior mesenteric ganglia), and is located in the upper abdominal retroperitoneum at the level of the T12 - L1 vertebrae. The preganglionic fibers of the greater (T5-10), lesser (T10-11), and least (T11-12) splanchnic nerves make up the celiac ganglion. There is a minor parasympathetic contribution from the vagus nerve. It typically surrounds the abdominal aorta, with most fibers lying anterior and anterolateral to it. It is anterior to the crura of the diaphragm and inferior to the celiac artery. It continues caudally to form the superior and the inferior mesenteric plexi. The celiac plexus contributes innervation to the abdominal viscera, including the stomach, small bowel, proximal large bowel, spleen, liver, gallbladder, pancreas, kidneys, and adrenal glands.
Anterior, lateral, and posterior (transaortic, periaortic, transcrural, and retrocrural) approaches to blocking the celiac plexus have been described. The posterior transcrural percutaneous approach is the most commonly used by pain physicians, followed by the retrocrural approach (which is technically a splanchnic nerve block). The advantage of the transcrural approach is that the needle tip remains precrural, which reduces the risk of neurologic complications as compared with the retrocrural approach. If the patient has significantly altered anatomy (i.e., a persistent mass in the area of celiac trunk origin, marked scoliosis, or previous extensive abdominal debulking surgery) or if the previous block was unsuccessful, the procedure may be performed using CT guidance.
A peripheral intravenous catheter should be placed prior to the procedure, 500 mL to 1000 mL of crystalloid intravenous (IV) fluid may be infused with additional IV fluid readily available, and appropriate standard noninvasive monitors should be placed. Using the posterior transcrural approach, the patient is positioned prone with their arms hanging off the bed or above the head, and with a pillow under the abdomen to reduce thoracolumbar lordosis. A strict sterile technique should be utilized throughout the procedure. Fluoroscopy or CT guidance is used to identify the tip of the 12th ribs bilaterally in order to distinguish the T12 and L1 vertebral bodies. The points 6 cm to 7 cm inferior and lateral to the transverse process of L1 are marked bilaterally, and skin overlying these sites should be anesthetized with a local anesthetic.
Under two plane fluoroscopic guidance, right and left needles are inserted at these marked entry sites and slowly advanced at approximately 45-degree oblique angle (and a slight cephalad angle) aiming at the L1 vertebral body of the corresponding side. After contacting the bone, depth is noted, and the needles are withdrawn to subcutaneous tissue and re-advanced at approximately a 30-degree oblique angle and advanced until the depth of previous bony contact. At that point, under AP and lateral views, the left-sided needle can be walked off the lateral surface of the L1 vertebral body and advanced slowly about 3 cm to 4 cm. If aortic pulsation is transmitted to the needle, the needle may either be redirected, or a transaortic approach may be performed. For the right side, the needle must be advanced in a similar fashion, but a bit further, 4 cm to 5 cm past bony contact. Assuming negative aspiration for blood, urine, or cerebrospinal fluid (CSF), a small amount of contrast is injected and should trace close to the midline, with no lateral spread. A test dose can be given thereafter, and if the patient has no lumbar dermatomal motor or sensory block after about 5 minutes, then the remaining medication consisting of 10 mL to 15 mL of local anesthetic or local anesthetic/neurolytic agent (ethanol, phenol) may be administered.
Complications and Side-effects[48][49]
Celiac plexus block may result in serious, non-transient complications in less than 2% of cases. Transient hypotension is an expected side effect as it is a sign of successful sympathetic de-efferentation (incidence is about 30% to 60%), so the physician should be ready to treat it (i.e., preprocedural PIV should be in place, the patient’s vital signs should be continuously monitored in the pre-, intra-, and post-procedural setting, and adequate IV fluid and vasopressors should be readily available). It is important to remember that geriatric, arteriosclerotic, or hypovolemic patients are most susceptible to large blood pressure drops as a result of this procedure. It is commonly recommended to infuse 500 mL to 1000 mL of crystalloid IV fluids before the procedure to mitigate the resulting orthostatic hypotension. Diarrhea due to unopposed parasympathetic activity is common as well, yet appears to subside within a few days after neurolysis in most cases. Interscapular back pain and hiccups have been described. Injury to viscera, aorta or inferior vena cava, and retroperitoneal hematomas may go undetected, as tachycardia and hypotension could be viewed as signs of an adequate block. Although very rare, direct or vasogenic nerve injury, infection, intravascular injection, pneumothorax, chylothorax, reactive pleurisy, hematuria, and impotence have been described as well. Intrathecal or epidural injection, the spread of solution to lumbar plexus or somatic nerves, particularly if a neuroablative chemical was used, can be devastating and lead to paralysis or death. Spasm of lumbar segmental arteries that perfuse the spinal cord due to irritation from phenol or ethanol has also been implicated in the pathogenesis of rare paraplegia.
Lumbar Sympathetic Block[50][51]
Specific Indications
Vascular insufficiency of lower extremities (atherosclerotic vascular disease, diabetic vascular insufficiency, Buerger disease, Raynaud disease, arteritis/collagen vascular disease, frostbite, embolisms); sympathetically mediated pain of the lower extremities, kidneys/ureters, genitals; complex regional pain syndrome I and II of the lower extremities; intractable renal colic; urogenital pain; post-amputation stump pain; phantom limb pain; frostbite; hyperhidrosis; acrocyanosis.
Technique
Lumbar sympathetic ganglia consist of 4-5 paired nodes that lie on the anterolateral surface of L1-L4 vertebrae, with the densest portion at the L2-L3 level. The lumbar sympathetic chain (LSC) is in very close proximity to the lumbar somatic nerves. It is anterolateral to the lumbar vertebral bodies and anterior to the psoas muscle. On the left, the LSC lies posterolateral to the aorta, and on the right, it lies posterior to the inferior vena cava.
Peripheral IV may be placed prior to the procedure, and standard noninvasive monitoring should be performed pre-, intra-, and post-procedurally. Lumbar sympathetic blocks are typically performed under fluoroscopic guidance, but may also be performed under CT guidance. A strict sterile technique is employed. The patient is positioned prone with a pillow under the abdomen to reduce lumbar lordosis. The L3 spinous process is identified radiographically in the AP view. The C-arm is obliqued to a 35-45 degree angle, and the skin entry point is identified (the inferolateral aspect of the L3 vertebral body) and anesthetized. A spinal needle (20 gauge to 25 gauge) is advanced to contact the inferolateral aspect of the L3 vertebral body, and advanced slowly with AP and lateral images are taken throughout. Under the lateral view, the needle should be advanced until it lies just anterior to the vertebral body. After negative aspiration, the contrast injected should delineate a vacuolated rather round shape consistent with solution expanding the retroperitoneal space (where sympathetic ganglia lie). Contrast should be seen lateral to the vertebral body (on lateral view) and anterior to the vertebral body (on AP view). If a strip-like image is produced, the needle is likely in the iliopsoas muscle is likely injected, and the needle should be repositioned. Test dose may be given next, and then the remaining 10 mL to 20 mL of anesthetic solution is injected (always after negative aspiration). Blockade at various lumbar levels, or a combination of levels, have been described with L1 being proposed as more adequate for renal or testicular pain and L4-L5 for foot pain; however, the block is most commonly performed at the L2 and/or L3 level(s).
Complications and Side-effects
Hypotension is very common after lumbar sympathetic blocks, especially if bilateral, due to intense vasodilation in the lower extremities and pelvis. Bleeding and soreness at the site of injection are typically transient. Groin pain and/or paresthesia may signify genitofemoral neuralgia or nerve injury, as the genitofemoral nerve is particularly vulnerable at the L4-5 level where it emerges from the psoas major muscle and lies anterior to the fascia in close proximity to the sympathetic chain. A genitofemoral nerve block may present as weakness and numbness in the groin, anterior thigh, and quadriceps. Damage to the viscera may occur if the needle penetrates retroperitoneal organs (urethra, kidney) or enters the peritoneum. Failure to ejaculate and impotence (especially with bilateral blocks), intravascular, epidural, or intrathecal injections, and allergic reactions may occur as well.
Superior Hypogastric Plexus Block[52]
Specific Indications
Chronic visceral and neuropathic pelvic pain caused by trauma/surgery, endometriosis, postoperative adhesions, inflammatory disease, interstitial cystitis, sympathetically mediated pelvic and/or rectal pain, post-prostatectomy penile and urethral pain, and malignant pain of the pelvic and/or rectal viscera unresponsive to conservative treatment.
Technique
The superior hypogastric plexus is located retroperitoneally, anterior to the L5–S1 vertebral body junction. The common and internal iliac arteries and veins are located on either side of the plexus.
The hypogastric plexus block is typically performed prone using a paraspinous technique, but other techniques have also been described. The transdiskal approach to superior hypogastric block appears to be equally effective as the classic posterior paraspinal approach. The anterior approach may be easier to perform and may reduce the risk of accidental neurologic injury as the needle would not be in close proximity to the nerve roots, but involves significant risk of organ and vasculature perforation (bowel, bladder, and/or pelvic vessels).[53]
Regardless of technique, strict sterile procedure and standard monitoring must be utilized throughout. Using the classic prone paraspinous approach, the patient should be positioned prone, and a pillow should be placed under the pelvis to flex the lumbar spine. The L4-L5 interspace is identified, and needle insertion sites are marked bilaterally 5 cm to 7 cm lateral of midline at L4–L5 interspace level. After anesthetizing the skin, a long spinal needle is inserted and advanced at about a 30-degree oblique angle and 30 degrees caudad toward the anterolateral part of the L5–S1 interspace. If positioned correctly, the AP radiographic view should reveal the tip of the needle at the junction of the L5-S1 vertebrae, with contrast spread in the midline region. In the lateral view, the needle tip lies just beyond the anterolateral margin of the L5 vertebral body, and contrast should spread anterior to the vertebral body. Assuming negative aspiration and appropriate contrast spread, 6 mL to 10 mL of local anesthetic and/or neurolytic agent is injected.
Complications and Side-effects
Possible complications include injury to the nerve roots or spinal cord, bleeding, retroperitoneal hematoma, perforation of pelvic viscera (including the ureters), intravascular, epidural, and intrathecal injections, infection, or dislodgement of an atherosclerotic plaque from the punctured vessel. Recall that the hypogastric nerves lie in close proximity to the iliac vessels. As the superior hypogastric plexus provides the major innervation to the urogenital system, blocking the plexus may cause retrograde ejaculation, which is usually transient. Trauma to the intervertebral disk and diskitis is possible with the transdiskal approach.
Ganglion Impar Block (Blockade of the ganglion of Walther)[13]
Specific Indications
Sympathetically mediated sacral, rectal, anal, genital, vulvar, and perineal pain (i.e., malignancy or postherpetic neuralgia), coccydynia, or pain secondary to endometriosis or proctalgia fugax.
Technique
The ganglion impar, as the name implies, is the solitary ganglion marking the end of the two sympathetic chains. It is a midline, retroperitoneal structure that is the most caudal ganglion of the sympathetic chain and is located anterior to the sacrococcygeal junction. It supplies partial sympathetic innervation to the genitals and the pelvic viscera.
The ganglion impar block may be performed via a prone technique or the transcoccygeal technique. Sterile technique and appropriate monitoring should be utilized throughout.
Using the prone technique, the patient is positioned prone, and a manually bent 22 gauge 3.5-inch spinal needle is inserted just anterior to the tip of the coccyx (through anococcygeal ligament) using AP and lateral fluoroscopic views with the concavity oriented posteriorly and advanced along the midline toward the sacrococcygeal junction. After negative aspiration, contrast is injected to confirm proper positioning, with a retroperitoneal spread of contrast. On the lateral view, contrast should be visualized to spread anterior to the coccyx in the precoccygeal space. Assuming negative aspiration, 4 mL to 8 mL of anesthetic and/or neurolytic agent is administered.
Using the transcoccygeal technique, the patient is positioned prone, and AP and lateral fluoroscopic views are used to identify the junction between the 1 and 2 coccygeal bones. The needle is advanced at this junction until the needle lies just anterior to the coccyx. Then, after negative aspiration, contrast is injected as described above, as is the chosen medication.
Complications and Side-effects
Proximity to the rectum can lead to visceral trauma and infection if the intestine is perforated. Furthermore, if this occurs, contamination may be tracked along the needle path upon needle removal, leading to fistula formation. Sacral nerve root injury, bladder, rectal and erectile dysfunction, periosteal injection are possible, though very rare.
Sympathetic Nerve Block