Chemical neurolysis of the inferior hypogastric plexus for the treatment of cancer-related pelvic and perineal pain

South Egypt Cancer Institute, Anesthesia, Intensive care and Pain Management, South Egypt Cancer Institute, Assiut, Egypt Correspondence: Dr Doaa Gomaa Ahmed, Anesthesia, Intensive Care and Pain Management, South Egypt Cancer Institute, Almethaque Street, Manshiet Elomra, PO Box 71516, Assiut, Egypt. Telephone 20-111-360-7950, fax 002-088-234-3268, e-mail doaagomaa78@yahoo.com The inferior hypogastric plexus is the primary autonomic neural coordinating centre in the pelvis. It integrates both parasympathetic and sympathetic output and receives input from the sacral level of the spinal cord (1,2). The inferior hypogastric plexuses are formed by efferent sympathetic fibres from the hypogastric nerves and from pelvic splanchnic nerves, preganglionic parasympathetic fibres from pelvic splanchnic nerves and visceral afferent fibres from pelvic viscera (3). Despite recent refinements in the technique for performing superior hypogastric plexus blocks, the lower pelvic organs and genitalia are innervated by nerve fibres from the presacral inferior hypogastric plexus, and these fibres are not readily blocked using paravertebral or transdiscal approaches (4). The inferior hypogastric plexus block was first described by Schultz (4) for the diagnosis and treatment of chronic pain conditions involving the lower pelvic viscera. It involves using a combination of local anesthetics/steroid and a trans-sacral approach under fluoroscopy. The purpose of the present study was to assess the feasibility, safety and efficacy of a newly introduced neurolytic inferior hypogastric block using phenol administered through the trans-sacral approach for the relief of cancer-related pelvic and perineal pain.

All patients underwent diagnostic blocks using local anesthesia one week before the neurolytic blockade was performed and had successful diagnostic test results (defined as a 50% reduction in pain scores measured using a visual analogue scale [VAS] within 24 h).Patients without successful diagnostic test results were excluded.
All patients were admitted to the hospital ward.An 18-gauge intravenous catheter was fixed, and patients received 1 L lactated Ringer's solution preprocedurally.All patients were then transported to the x-ray room and received conscious sedation using 0.1 mg/kg midazolam and 1 μg/kg fentanyl.Standard monitoring recommended by the American Society of Anesthesiologists were used, including electrocardiography, blood pressure and pulse oximetry measurements.

Procedure
The patient was placed prone on the x-ray table.An anterior-posterior scout view of the sacrum was obtained and the C-arm was tilted cephalad to view the sacral foramina 'end-on' as circles or semicircles on each side of the midline.Using fluoroscopy, an entrance point was marked on the skin surface 1 cm to 2 cm lateral to the lateral edge of the S2 or S3 sacral foramen on the side to be blocked.The foramen that was most easily visible was usually chosen.This block may be performed through S1, S2, S3 or S4, although S2 is usually the preferred access level.After the skin was cleaned, a skin wheal was raised over the entrance site and a path of anesthesia toward the targeted sacral foramen was infiltrated.An appropriately bent 3.5 inch, 25-gauge spinal needle was passed through the anesthetized track and advanced to the lateral aspect of the dorsal sacral foramen until contact with bone was made.The needle was advanced slowly and incrementally under fluoroscopic guidance through the dorsal sacral foramen toward the medial interior edge of the ventral sacral foramen, until contact was made with the medial bony edge of the ventral sacral foramen.When sacral paresthesia was encountered, the needle was retracted and rotated slightly to move past the sacral nerve root.A small, incremental dose of 1% lidocaine (0.1 mL to 0.3 mL) during needle advancement improved patient comfort without creating blockade of sacral nerve roots.The needle was manoeuvred along the medial edge of the ventral sacral foramen to exit the ventral foramen as medially as possible.The needle was advanced anteromedially an additional 1 mm toward the midline presacral plane and the contrast medium was injected under live continuous fluoroscopy to ensure negative vascular uptake.If the needle was in the optimal position, the contrast would spread cephalad and caudad along the presacral plane conforming to the midline, ventral surface of the sacrum.
When proper needle tip position was assured, 6 mL to 8 mL of 10% phenol in saline was injected in each side.If injected contrast and medication spread across the midline from the side of needle placement, then a unilateral block could be sufficient.More commonly, however, contrast spread is primarily unilateral, necessitating a bilateral needle placement to complete blockade of the right and left inferior hypogastric plexuses (Figure 1, Figure 2).
Following the block, the patients were taken to the postanesthetic care unit for the following 24 h.

Parameters assessed
Pain intensity was measured using a 10 cm VAS, ranging from 0 ('no pain') to 10 ('worst imaginable pain').VAS scores were measured before the procedure and at 30 min, 60 min, 2 h, 6 h, 24 h, one week, two weeks, four weeks and two months after the procedure.A failed block was defined as failure to lower VAS scores by 50% of the preprocedural VAS score.Total MST consumption was recorded preprocedurally, at the first 24 h postprocedurally in the postanesthetic care unit and at follow-up visits.The time required to perform the block, any complications during or after the procedure (including transient paresthesia, rectal puncture, vascular penetration of one of the pelvic vessels, hematoma, infection, dural puncture, bowel/bladder dysfunction, pain on injection, hypotension from the sympathetic block or any other complication) and hemodynamic parameters (blood pressure, heart rate, oxygen saturation) before, during and after the procedure for 24 h at the postanesthetic care unit were also examined.The patients were discharged after 24 h and were followed-up for two months, at weeks 1, 2 and 4, and at two months.

Statistical analysis
Statistical analysis was performed using SPSS version 16 (IBM Corporation, USA).Values are presented as mean ± SD, range, percentage and number.Statistical analysis was performed using Wilcoxon signed ranks test to assess the change in VAS scores and morphine consumption from baseline.Differences were considered to be statistically significant at P<0.05.

RESULTS
A total of 20 patients were enrolled in the present study and underwent inferior hypogastric plexus block.Two patients died during the follow-up period and were excluded from the analysis.Demographic data, clinical data and the mean duration of the procedure are presented in Table 1.
The mean (± SD) VAS score of the patients was 7.22±1.31before the block was performed.VAS scores decreased significantly (P<0.05)immediately after injection compared with the preprocedural period and was sustained during all follow-up assessments (Table 2, Figure 3), with maximum reduction (by 43.8% of the baseline VAS score [P<0.05])observed after one week.
All patients were either receiving high doses of MST with inadequate pain control or were limiting their morphine intake despite significant pain relief because of its side effects (sedation, nausea, vomiting and constipation).Mean consumption of MST before the block was 106.67±32.90mg/day, and was significantly reduced at 24 h, one week, two weeks and four weeks after the block (P<0.05),but was not significantly reduced after two months, with maximum  3).
Successful pain relief (VAS score below 50% of the preprocedural measured VAS score) occurred in eight patients (44.4%) based on immediate pain relief and no evidence of complications.One-half of the patients had experienced perineal pain, and the other one-half had experienced either pelvic pain or pelviperineal pain.
No significant changes were observed in hemodynamic variables (blood pressure, heart rate and oxygen saturation) measured during the first 24 h after the procedure.Complications encountered during the procedure are listed in Table 4.

DISCUSSION
The bilateral inferior hypogastric plexuses are interconnected networks of nerves lying within the presacral tissues, which lie along the anterior surface of the sacrum medial to the foramina sacralia on either side of the rectum, ventral to the S2, S3, and S4 spinal segments (3,5).Schultz (4) was the first to describe the inferior hypogastric plexus block through the trans-sacral approach under fluoroscopy, using a local anesthetic/steroid combination, for the diagnosis and treatment of chronic pain conditions involving the lower pelvic viscera.The present study is the first to report the use of phenol for neurolysis of the inferior hypogastric plexus in the treatment of cancer-related pelvic and perineal pain.
Visceral pelvic pain occurs in association with oncological disease (6,7), particularly bladder cancer, which is the most common malignancy among Egyptian men.This has previously been attributed to Schistosoma infection (8).Approximately 25% of patients have an inoperable tumour on presentation (9).This served as motivation for our group to examine the efficacy of the newly described sympathetic axis block using phenol.
Schultz reported a success rate of 73% when performing 15 blocks on 11 patients who suffered from chronic pelvic pain, with mean (± SD) VAS scores of 7.4±2.3and 5.0±2.7 pre-and postprocedure, respectively.We observed a lower success rate (44.4%), with VAS scores reduced from 7.22±1.31preprocedurally to 4.06±1.73postprocedurally.This difference in success rate can be attributed to the density of the surrounding connective tissue (10) and the possible involvement of structures other than visceral by the malignancy (11), which may limit the spread of the phenol.
Transient paresthesia was the most common adverse event encountered during trans-sacral blockade of the inferior hypogastric plexus, occurring in 38.8% of the procedures performed.This occurs mainly because the sacral spinal nerves, with their dorsal and ventral rami, course close to the advancing needle and may be occasionally contacted by the needle tip (4).Transient paresthesia can be minimized with slow and careful advancement of the needle using frequent injections of small volumes of diluted local anesthetic as the needle advances.If paresthesia begins to occur, one can direct the path of the needle around the path of the traversing nerve before advancing further by rotating the bent needle tip slightly, as described in the original report of the technique.Performing the block on patients with pelvic, perineal or pelviperineal cancer-related pain resulted in better pain relief in patients with low pelvic and perineal pain compared with individuals with isolated pelvic pain.
Cancer patients presenting with low pelvic pain combined with perineal pain (anal pain or pain arising from the genitalia) may benefit from inferior hypogastric plexus block rather than superior hypogastric plexus block and ganglion impar block, especially because this area is innervated by nerve fibres from the presacral inferior hypogastric plexus that will not be blocked by the superior hypogastric plexus block, even with the refinement of its techniques to include either paravertebral or transdiscal approaches (4).
Whenever pain is amenable to be treated by an inferior hypogastric plexus block, it is safer to perform this procedure than the superior hypogastric plexus block because it eliminates the risk of injuring the structures overlying the superior hypogastric plexus such as the bowel, bladder or common iliac artery.
The anterior approach to the superior hypogastric plexus block carries a risk of infection when passing through the bowel; furthermore, the transdiscal approach is associated with a potential risk of discitis, disk rupture or disk herniation, and requires preparation with antibiotics.
Regarding the risk of rectal injury during the block procedure, in the case of the inferior hypogastric plexus block, this may occur if the needle is advanced too deeply into the presacral tissue, and it can be easily avoided by careful visualization of the needle depth using the lateral fluoroscopy because the rectum is separated from the ventral surface of the sacrum by >1 mm (4).However, in the case of ganglion impar block involving the conventional transanococcygeal membrane technique, there is a need for continuous rectal examination by the operator with the index finger to prevent rectal perforation (20).
Inferior hypogastric plexus block is a good alternative technique for the treatment of cancer-related pelvic, perineal or pelviperineal pain, with better results in patients with prominent lower pelvic and perineal pain.Better success rates may be achieved if the technique is re-evaluated in selected patients with low pelvic or perineal pain, and if other radiological techniques, such as ultrasonography or computed tomography, are incorporated.

CONCLUSION
The inferior hypogastric plexus block is a good alternative neurolytic technique for the treatment of low pelvic and perineal pain.However, large, well-controlled studies and refinement of the technique using other radiological methods are needed to improve the safety and efficacy of this new neurolytic technique.

Figure 1 )Figure 2 )
Figure 1) Advancement of the needle through the dorsal sacral foramen toward the medial interior edge of the ventral sacral foramen

TABLE 1 Patient characteristics, clinical data and mean duration of procedure Characteristic
Data presented as mean ± SD, unless otherwise indicated