# Interventional Techniques for Cancer Pain

## Introduction

Despite optimal pharmacologic management following the WHO analgesic ladder, approximately 10-20% of cancer patients experience refractory pain that is inadequately controlled or limited by intolerable opioid side effects. Interventional techniques serve as the proposed fourth step of the analgesic ladder, offering targeted analgesia that can dramatically reduce systemic opioid requirements, improve quality of life, and restore function in selected patients. Early referral for interventional evaluation should be integrated into comprehensive cancer pain management rather than reserved as a last resort.

## Neuraxial Analgesia

### Epidural Analgesia

Epidural analgesia is indicated for localized or regionalized cancer pain in the thoracic, abdominal, pelvic, or lower extremity distributions that has proven refractory to systemic opioids, or when opioid dose escalation is producing dose-limiting side effects. A percutaneous epidural catheter is placed at the vertebral level corresponding to the relevant pain dermatomes and tunneled externally for prolonged use. The medications infused are typically combinations of a low-concentration local anesthetic (bupivacaine 0.0625-0.125%) and an opioid (hydromorphone 10-50 mcg/mL or fentanyl 2-5 mcg/mL). The synergistic interaction between these two drug classes reduces the dose requirements of each agent.

Epidural analgesia offers several advantages: rapid onset, flexible dose titration, reversibility, and the ability to trial the approach before committing to a more permanent intrathecal pump. Its limitations include catheter migration, infection risk (including epidural abscess), dural puncture, and fibrosis around the catheter tip that can reduce efficacy over weeks to months. It also requires an external pump and regular dressing changes. Epidural analgesia is typically appropriate for patients with a life expectancy of weeks to a few months; for longer durations, intrathecal drug delivery is preferred.

### Intrathecal Analgesia

Intrathecal analgesia is indicated for cancer pain refractory to systemic opioids, epidural analgesia, or other interventional techniques. When life expectancy exceeds 3-6 months, an implantable pump is favored; for shorter prognoses, an externalized catheter may suffice. The intrathecal catheter is placed via a percutaneous or surgical approach and connected to a programmable implantable pump (such as the Medtronic SynchroMed II), which is housed in a subcutaneous abdominal pocket.

The Polyanalgesic Consensus Conference (PACC) guidelines recommend morphine or ziconotide as first-line monotherapy. Morphine is FDA-approved for intrathecal use and remains the most commonly used agent. Ziconotide, an N-type calcium channel blocker, is a non-opioid alternative that is also FDA-approved for intrathecal delivery. Hydromorphone is widely used off-label, and adjuvants such as bupivacaine and clonidine (particularly useful for neuropathic pain) can be added for refractory cases.

The advantages of intrathecal delivery are substantial. The intrathecal-to-oral morphine ratio is approximately 1:300, meaning dramatic reductions in systemic opioid exposure. Dosing is programmable, systemic side effects are reduced, and the pump reservoir is refilled percutaneously every 1-6 months. Complications include catheter-tip granuloma formation (especially with high-concentration morphine), pump pocket seroma or infection, catheter migration or fracture, post-dural puncture headache, and the risk of overdose or underdose from programming errors.

<image>Medical illustration showing a cross-sectional view of the thoracic spine with both epidural and intrathecal catheter placements, demonstrating the epidural catheter tip in the dorsal epidural space and the intrathecal catheter tip within the subarachnoid space surrounded by cerebrospinal fluid, with labeled anatomy including dura mater, arachnoid mater, spinal cord, and nerve roots, plus an inset showing the implantable intrathecal pump in the subcutaneous abdominal pocket connected to the spinal catheter</image>

## Celiac Plexus Neurolysis

### Indications and Anatomy

The primary indication for celiac plexus neurolysis is visceral abdominal pain from pancreatic cancer, which has the strongest evidence base. It is also used for gastric, hepatobiliary, and other upper abdominal malignancies. The celiac plexus is the largest autonomic plexus in the body, located retroperitoneally at the T12-L1 level, anterior to the aorta and surrounding the origin of the celiac trunk. It receives sympathetic input from the greater (T5-T9), lesser (T10-T11), and least (T12) splanchnic nerves.

### Technique

Several approaches are available. The classic posterior paravertebral approach uses bilateral needle placement at L1. An anterior CT-guided transgastric approach is available for patients who cannot lie prone. Endoscopic ultrasound (EUS)-guided neurolysis is increasingly preferred for pancreatic cancer because of its direct visualization and single-session integration with diagnostic procedures. The most commonly used neurolytic agent is absolute alcohol (50-100%), with phenol (6-10%) as an alternative, typically using 15-20 mL per side. Guidance modalities include fluoroscopy with contrast, CT, or EUS. Splanchnic nerve neurolysis, which targets the splanchnic nerves at T11-T12 posterior to the diaphragmatic crura, is an alternative approach that may have a more favorable safety profile.

### Evidence and Outcomes

Celiac plexus neurolysis achieves significant pain relief in 70-90% of patients. Meta-analyses demonstrate reduced opioid consumption and improved quality of life compared to pharmacologic management alone. Importantly, evidence supports early neurolysis -- at the time of diagnosis in patients who already have pain -- rather than waiting for pharmacologic failure. The Wyse et al. (2011) randomized controlled trial showed that early EUS-guided neurolysis provided superior pain control and tended toward improved survival. Complications include transient diarrhea (44%) and orthostatic hypotension (38%), both resulting from the sympathectomy effect. Rare but serious complications include paraplegia (less than 1%, from injury to the artery of Adamkiewicz), retroperitoneal hemorrhage, and pneumothorax.

## Superior Hypogastric Plexus Block

The superior hypogastric plexus block targets visceral pelvic pain from cervical, endometrial, ovarian, bladder, rectal, or prostate cancer. The superior hypogastric plexus is a retroperitoneal structure at the L5-S1 level, anterior to the L5 vertebral body, situated between the common iliac vessels. The standard approach is posterior paramedian under fluoroscopy or CT guidance, with bilateral needle placement anterior to the L5-S1 disc. A diagnostic block with local anesthetic is performed first; if effective, neurolysis with alcohol or phenol follows. A transdiscal approach using a single midline needle through the L5-S1 disc is technically simpler but carries a risk of discitis.

Uncontrolled studies report 60-70% pain reduction in pelvic cancer pain. Randomized controlled trial data are limited, and the procedure is commonly used based on clinical experience and expert consensus. Complications include vascular injury to the iliac vessels, discitis (with the transdiscal approach), transient lower extremity weakness, and rare bladder or sexual dysfunction.

<image>Anatomical illustration showing a sagittal view of the retroperitoneum with the celiac plexus at the T12-L1 level surrounding the celiac trunk anterior to the aorta, and the superior hypogastric plexus at the L5-S1 level between the common iliac arteries, with needle trajectories for both neurolytic procedures shown from the posterior approach, and labeled structures including the aorta, inferior vena cava, vertebral bodies, diaphragmatic crura, and splanchnic nerves</image>

## Cordotomy

Cordotomy is the ablation of the lateral spinothalamic tract in the anterolateral spinal cord, which eliminates contralateral pain sensation below the level of the lesion. It is indicated for unilateral, somatic cancer pain below the C5 dermatome that has been refractory to all other measures, and is most commonly used for mesothelioma and Pancoast tumor pain. The procedure is performed percutaneously at the C1-C2 level under CT guidance using radiofrequency ablation, with the patient under local anesthesia to allow real-time neurologic monitoring. Impedance measurement confirms that the electrode is positioned in the anterolateral cord.

Initial pain relief is achieved in 80-95% of patients, though efficacy may diminish over 6-12 months due to neuroplasticity and the development of mirror-image pain. Complications include ipsilateral motor weakness (from proximity to the corticospinal tract), respiratory dysfunction (from reticulospinal tract injury, which is particularly hazardous with bilateral cordotomy and can produce "Ondine's curse"), dysesthesia, and bladder dysfunction. Because of diminishing efficacy over time, cordotomy is typically reserved for patients with a life expectancy of less than one year. Bilateral cordotomy is avoided because of the respiratory risk. The procedure is available at only a limited number of specialized centers, and its use has declined with advances in intrathecal drug delivery, though it remains a valuable option for carefully selected patients.

## Intrathecal Drug Delivery for Refractory Cancer Pain

### Patient Selection

Appropriate candidates for intrathecal drug delivery are those who have failed systemic opioid optimization, who experience intolerable side effects from systemic opioids (cognitive impairment, myoclonus, severe constipation), or whose pain requires interventional management with a life expectancy exceeding 3 months. An intrathecal catheter trial lasting 1-3 days is typically performed to confirm efficacy and tolerability before pump implantation, although some practitioners proceed directly to implantation in cancer patients with clear indications. The Smith et al. (2002) landmark randomized controlled trial demonstrated that intrathecal drug delivery combined with comprehensive medical management provided superior pain relief, fewer drug toxicities, and improved survival compared to comprehensive medical management alone.

### Drug Selection (PACC Guidelines)

| Line | Recommended Agents | Notes |
|------|-------------------|-------|
| Line 1 | Morphine monotherapy OR Ziconotide monotherapy | Both FDA-approved for intrathecal use |
| Line 2 | Morphine + bupivacaine OR Hydromorphone ± bupivacaine | Hydromorphone widely used off-label |
| Line 3 | Morphine/hydromorphone + bupivacaine + clonidine | Clonidine particularly useful for neuropathic pain |
| Line 4 | Sufentanil, fentanyl, or other combinations | Reserved for refractory cases |

The PACC guidelines organize intrathecal drug selection into a tiered system. Line 1 recommends morphine monotherapy or ziconotide monotherapy. Line 2 includes morphine plus bupivacaine, hydromorphone monotherapy, or hydromorphone plus bupivacaine. Line 3 adds clonidine to the regimen, typically as morphine or hydromorphone combined with bupivacaine and clonidine. Line 4 encompasses sufentanil, fentanyl, or other combinations. Ziconotide deserves special mention as a non-opioid option that carries no risk of respiratory depression, tolerance, or dependence, though it requires slow titration because of CNS side effects including dizziness, nausea, and psychiatric symptoms. In many protocols, ziconotide cannot be combined with intrathecal opioids.

### Pump Management

Initial dosing is based on trial results, with gradual titration and reassessment at each refill visit. Refill frequency depends on reservoir volume (20 or 40 mL) and infusion rate, typically ranging from every 1 to 6 months. End-of-life planning is essential: the pump management plan must be communicated to the patient's palliative care and hospice teams, because abrupt discontinuation of intrathecal opioids can cause life-threatening withdrawal.

## Clinical Pearls

Early referral for interventional cancer pain management improves outcomes; waiting until all pharmacologic options are exhausted is a disservice to the patient. Celiac plexus neurolysis should be considered early in the management of pancreatic cancer pain, since the evidence supports superior outcomes with early intervention. Intrathecal drug delivery is the only interventional cancer pain technique supported by a randomized controlled trial demonstrating improved survival (Smith et al., 2002). Percutaneous cordotomy remains a powerful but underutilized tool for unilateral somatic cancer pain, requiring specialized expertise and careful patient selection. Coordination of intrathecal pump management with the patient's hospice or palliative care team is non-negotiable to prevent catastrophic withdrawal at the end of life.

## References

1. Smith TJ, Staats PS, Deer T, et al. Randomized clinical trial of an implantable drug delivery system compared with comprehensive medical management for refractory cancer pain: impact on pain, drug-related toxicity, and survival. *J Clin Oncol*. 2002;20(19):4040-4049.
2. Wyse JM, Carone M, Paquin SC, Usatii M, Sahai AV. Randomized, double-blind, controlled trial of early endoscopic ultrasound-guided celiac plexus neurolysis to prevent pain progression in patients with newly diagnosed, painful, inoperable pancreatic cancer. *J Clin Oncol*. 2011;29(26):3541-3546.
3. Deer TR, Pope JE, Hayek SM, et al. The Polyanalgesic Consensus Conference (PACC): recommendations on intrathecal drug infusion systems best practices and guidelines. *Neuromodulation*. 2017;20(2):96-132.
4. Kanpolat Y, Savas A, Bekar A, Berk C. Percutaneous controlled radiofrequency trigeminal rhizotomy for the treatment of idiopathic trigeminal neuralgia: 25-year experience with 1600 patients. *Neurosurgery*. 2001;48(3):524-534.