Sacral nerve stimulation (SNS) also termed sacral neuromodulation (SNM), is a minimally invasive surgical procedure in which a device (pulse generator) is implanted in the body. The device delivers mild electrical pulses, resulting in continuous electrical stimulation of the sacral spinal nerves (usually sacral spinal nerve 3). It is an example of neuromodulation. Sacral nerve stimulation is used to treat various pelvic disorders, including urinary incontinence, urinary urgency, urinary frequency, urinary retention, overactive bladder, fecal incontinence, constipation, and low anterior resection syndrome.
Indications SNS may be indicated if non surgical treatments do not work. SNS has been used for many different pelvic conditions. Sometimes more than one indicated condition coexists. For example, pelvic pain might be combined with bladder, bowel, or sexual dysfunction.
Bladder dysfunction Urinary incontinence Overactive bladder. Urinary urgency Urinary frequency Urinary retention. Voiding dysfunction. Bowel dysfunction Fecal incontinence Constipation. Low anterior resection syndrome. This condition often occurs after low anterior resection surgery and radiotherapy for rectal cancer. It may be caused by different factors such as sphincter injury, fibrosis, and nerve damage. The symptoms are varied, including stool fragmentation, fecal urgency, and fecal incontinence. Hirschsprung's disease. Chronic pelvic pain. Bladder pain syndrome. Interstitial cystitis. Levator ani syndrome. Pudendal nerve entrapment / pudendal neuralgia.
Bladder dysfunction SNS is used for several types of neurogenic bladder disorders such as multiple sclerosis, meningomyelocele, and spinal cord injury. It is used for overactive bladder which is non responsive to non surgical treatment. SNS is also indicated for non-obstructive urinary retention, i.e., inability or difficulty emptying the bladder for reasons other than physical blockage of the urinary tract.
Bowel dysfunction Originally, SNS was used in cases of moderate or severe fecal incontinence where the person had a limited defect of the sphincter or an intact external anal sphincter. Later, SNS started to be used for people who had sphincter defects. SNS has been used for Hirschsprung's disease. SNS is sometimes used in combination with cecostomy.
Chronic pelvic pain SNS has been used for a variety of chronic pelvic pain conditions, such as interstitial cystitis, bladder pain syndrome, functional anorectal pain, endometriosis, pudendal neuralgia, and post-surgical, obstetric, and idiopathic pelvic pain (of unknown cause).
Contraindications Urinary obstruction. Active infection in pelvic region. Severe or rapidly deteriorating neurologic disease. Patient not able to operate the device.
Technique There are two main approaches: one stage SNS and two stage SNS.
Trial period In two stage SNS, a trial period is conducted first to test what the effects of SNS would be for individuals being considered for implantation of a permanent implantable pulse generator device. Permanent SNS is an expensive process, and the implantation procedure is slightly more invasive. The trial period is sometimes termed temporary percutaneous nerve evaluation (PNE). There is some variation in the technique for the trial period. The placement of the leads may be carried out under general anesthesia, local anesthetic with sedation, or local anesthesia alone. The trial period can be basic with 1-2 temporary unipolar leads, or more advanced with a tined lead. A tined lead has small, flexible "tines" (or barbs) which anchor the lead in place and reduce the risk of migration (moving out of position). The temporary unipolar stimulation lead and electrode are placed percutaneously (through the skin). The electrode is connected to an external pulse generator. A trial period can also be carried out with a quadripolar lead, which has 4 electrodes at the end. PNE has a slightly higher failure rate, but the quadripolar lead has a slightly higher risk of infection. The trial period usually lasts 1–2 weeks, sometimes 3 weeks. If the trial period has positive results, then permanent SNS is possible. According to some reports, the results of the trial period do not predict the long term outcome of permanent SNS.
Permanent implantation There are different techniques for permanent SNS. The pulse generator is implanted to the side of the sacrum, below the level of the iliac crest. The lead is normally placed through the S3 foramen (transforaminal). Sometimes the leads are placed via a lumbar epidural puncture, via the sacral hiatus, or using laparoscopic approach. Sometimes a tined quadripolar lead is used. Sometimes a single lead is used. The leads may be placed on only one side, or on both sides. Usually the electrical stimulation is applied to the S3 nerve, but sometimes S4 in addition, or even more rarely in combination with S1 and S2.
Device (implantable pulse generator) The implanted devices in SNS are termed implantable pulse generators. Smaller, rechargeable devices are now available. Smaller devices may be more comfortable for thinner individuals, and may be less likely to cause pain at the site of implantation. The Interstim II pulse generator is approximately the size of a cardiac pacemaker. This size seems to be suitable for most patients. Indeed, smaller devices may be more difficult to implant in obese individuals. The battery life of rechargeable devices is approximately 15 years. It is likely that a surgical procedure for other reasons, e.g. lead replacement, would be required before the battery life ran out. The battery in the InterSim II lasts 5–7 years. Rechargeable pulse generators require recharging every 1–2 weeks with a recharger. The device may heat up slightly during recharging. Recharge free devices are more suitable for individuals who would have poor compliance with recharging and programming the device for dexterity, cognitive, or motivation reasons. Some available pulse generators are:
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