6/16/2016 IOM APPROACHES TO THE PUDENDAL NERVE TEAL TAYLOR, REEGT/REPT/CNIM EVOKES, LLC A SENSITIVE SUBJECT: I DON T WANT TO WEAR A DIAPER

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1 IOM APPROACHES TO THE PUDENDAL NERVE TEAL TAYLOR, REEGT/REPT/CNIM EVOKES, LLC A SENSITIVE SUBJECT: I DON T WANT TO WEAR A DIAPER In IOM we continuously work to protect the Sensory and Motor Function of the Limbs for our patients But what about the more sensitive subjects: I can t control my urine output it dribbles I have no control of my bowels I can t get and erection, or orgasm or enjoy sex anymore The pudendal and lower sacral nerves play an important role in the daily function of a person IOM monitoring and protection of the pudendal nerves that assist in controlling all of the above functions is possible! WHY IS THE PUDENDAL NERVE IMPORTANT The Pudendal Nerve is responsible for important daily activities Sensation to the external genitalia and anus in both sexes Motor supply to the various pelvic muscles including Anal Sphincter and Urethral Sphincter Damage to the Pudendal Nerve may cause: Sensory loss to musculature Urinary or fecal incontinence Sexual Reproduction Issues 1

2 PUDENDAL NERVE The pudendal nerve has both motor and sensory functions. It does not carry parasympathetic fibers, but does carry sympathetic fibers. Sympathetic Fibers: allows for muscles to relax, longer pathway and slower system Parasympathetic Fibers: allows for muscle contraction, shorter neurons and faster system The pudendal nerve is responsible for the afferent component of penile/clitoral erection; is also responsible for ejaculation. Branches also innervate muscles of the perineum and pelvic floors As it functions to innervate the External Urethral Sphincter it is responsible for the tone of the sphincter mediated via acetylcholine release. THE PUDENDAL NERVE Major branch from the sacral plexus Paired Nerve Derived from the ventral rami S2-S4 Nerve divides into 3 branches: Inferior rectal nerve Perineal nerve Dorsal nerve of the penis (in males) or the Dorsal nerve of the clitoris (females) The pudendal nerve may vary in its origins Pudendal nerve may actually originate off of the sciatic nerve therefore damage to the sciatic nerve can affect the pudendal nerve as well. Sometimes dorsal rami of the first sacral nerve contribute fibers to the pudendal nerve, and even more rarely S5 Typical Orientation of Pudendal Nerve Fibers S2: 60.5% Fibers S3: 35.5% Fibers Single Root: 18% Single Unilateral Nerve Root: 7.6% PUDENDAL NERVE ANATOMY Pudendal Motor Neurons on Onuf s Nucleus lodge within the ventral gray near the distal tip of the conus medullaris Proximate to the midline filum terminale, efferent/afferent roots (S1), S2-S4 descend in close apposition to the sacral parasympathetic fibers within the cauda equina Ventral Rami of the somatic fibers exit foramen to for mixed PN And of course: A Video is Even Better! Virtual Pudendal Nerve 2

3 PELVIC FLOOR ANATOMY REVIEW: MALE PELVIC FLOOR ANATOMY REVIEW: FEMALE CLINICAL TESTING OF PUDENDAL NERVE DYSFUNCTION The bulbocavernosus reflex (BCR) or "Osinski reflex" is a polysynaptic reflex that is useful in testing for spinal shock and gaining information about the state of spinal cord injuries Procedure The test involves monitoring internal/external anal sphincter contraction in response to squeezing the glans penis or clitoris, or tugging on an indwelling Foley catheter.. This reflex can also be tested electrophysiologically, by stimulating the penis or vulva and recording from the anal sphincter. Trauma The reflex is spinal mediated and involves S2-S4. The absence of the reflex in a person with acute paralysis from trauma indicates spinal shock whereas the presence of the reflex would indicate spinal cord severance. Typically this is one of the first reflexes to return after spinal shock. Lack of motor and sensory function after the reflex has returned indicates complete Spinal Cord Injury. Absence of this reflex in instances where spinal shock is not suspected could indicate a lesion or injury of the conus medullaris or sacral nerve roots. 3

4 THE CLINICAL BCR FOR CLINICAL EVALUATION IONM METHODS FOR MONITORING THE PUDENDAL NERVE Somatosensory Recording Pudendal SSEP Stimulates the Dorsal Nerve and Records from the somatosensory cortex Averaged Response ( Avg) Bulbocavernosus Reflex (BCR) Polysynaptic Reflex Testing Like a MEP recording Single or Double train Stimulation Records a single polyphasic wave or double polyphasic wave dependent upon stimulation setup Stimulate from the dorsal nerve and records from the anal sphincter Direct Pudendal Stimulation Useful is dorsal rhizotomies Direct Stimulation to lower roots to identify the roots associated with pudendal nervefunction PUDENDAL NERVE MONITORING: PUDENDAL SSEP W Morphology Positive (+) initial phase with a latency of 40 (+/- 2 milliseconds) Amplitude roughly equal to that of the P37 response in PTN Stimulation Averaging Clinically over 100 averages IOM typically resolve in Averages (Echer 2014) Longer averaging typically does not resolve a present and replicating response Pudendal SSEP at Varying Stimulation Top Line: 2mA Middle Line: Stimulation Threshold Bottom line: 2x Above Sensory Threshold 4

5 PUDENDAL NERVE MONITORING: PUDENDAL SSEP MALE SET-UP Electrode Placement Stimulating Electrodes Electrode Placement Recording Electrodes Fz Reference 2 cm posterior to Cz =Cathode =Anode PUDENDAL NERVE MONITORING: PUDENDAL SSEP BILATERAL FEMALE SET-UP Electrode Placement Stimulating Electrodes Cathode placed adjacent to the clitoris on the left and on the right, respectively, at 3 and 9 o clock positions. The anode was placed between the labia minora and labia majora on the same side. Electrode Placement Recording Electrodes Fz Reference 2 cm posterior to Cz =Cathode =Anode PUDENDAL NERVE MONITORING: SSEP PARAMETERS Stimulation Delivery square wave pulses 0.5ms in duration frequencies of 4.7 hertz (Hz) Stimulation 15-25mA Recording Parameters Filters: Hz Avoid: LFF greater than 50Hz and HFF Less than 3000Hz Averages: In most cases, if it is not present after 100 Averages it is not a true response Waveform of Interest: P40 Maximal at Cz(Guerit and Opsomer- 1991) Multiphasic W morphology 5

6 PUDENDAL SSEP STUDY COHEN 1991 Pudendal SSEP utilized in IOM for Orthopedic surgeries below S1 154 Patients 1 False Positive due to loosening of electrodes 1 True Positive due to traction on the nerve or sacral roots causing a 3ms latency shift In general, a wider population of procedures and testing is needed to validate the use of SSEPs in IOM FUTURE OF PUDENDAL SSEP IN IOM Tibial Nerve SSEPs monitors S1 and Above Pudendal SSEP allows for monitoring of nerve roots S2/3 and above Could help detect cauda equina injuries that PTN SSEPs can not detect Pudendal Nerve SSEPs may serve as a substitute when PTN SSEP are unobtainable due to: Limb amputation, Peripheral Neuropathy, Lack of Response from PTN or Peroneal Nerve Stimulation Adequate and easily added modality for monitoring dorsal column of spinal cord UNILATERAL OR BILATERAL STIMULATION OF PUDENDAL NERVE: THE STIMULATION ARGUMENT Lateralization Nothing published that significantly indicates importance of lateralizing stimulation and recordings in all pudendal nerve monitoring modalities. Most authors conclude that stimulation activates bilateral pudendal nerves Anode vs Cathode Stimulation Authors report utilizing either anode or cathodal stimulation with similar results Cathodal Stimulation appears prominent is most research reviewed No papers found to review which approach is most efficacious 6

7 WHAT IS A BULBOCAVERNOSUS RESPONSE? In Clinical Studies, the Bulbocavernosus Response (BCR) is elicited by squeezing the glans penis and digitally palpating the contraction of the bulbocavernosus (BC) muscle. Bors and Blinn (1959) first used this reflex for examination of the neurogenic bladder. In intraoperative monitoring the (BCR) is an evoked response to stimuli at the dorsal nerve of the penis or clitoris and is recorded from the anal sphincter muscle that innervates the pudendal nerve. This test has been demonstrated to correlate with Erectile Dysfunction and is recordable in all patients despite conditions like: Diabetic neuropathy Multiple sclerosis with conus demyelination Alcoholic neuropathy Spinal cord injured patients with sacral cord involvement This test serves to estimate the integrity of the somatic part of the pudendal nerve along its entire course through the peripheral and central nervous system. PUDENDAL NERVE MONITORING: BCR Bulbocavernosus Response (BCR) Oligosynaptic Reflex Neural conduction pathway interrupted by only a few synaptic junctions that is made up of a sequence of only a few nerve cells Typical Latency of 33ms Polysynaptic Responses at 55ms In women, more sensitive to BCR testing IOM than Clinically Successfully recorded in all age patients, including Neonates THE REFLEX ARC 7

8 PUDENDAL NERVE MONITORING: MALE BILATERAL BCR SET-UP =Cathode =Anode = Recording Paired Sphincter electrodes placed left or right in respect to stimulation side Electrode Placement Stimulating Electrodes PUDENDAL NERVE MONITORING: FEMALE BILATERAL BCR SET-UP Cathode placed adjacent to the clitoris on the left and on the right, respectively, at 3 and 9 o clock positions. The anode was placed between the labia minora and labia majora on the same side. Electrode Placement Recording Electrodes Anal Sphincter Muscle =Cathode =Anode = Recording Paired Sphincter electrodes placed left or right in respect to stimulation side Unilateral Set-up: PUDENDAL NERVE MONITORING: BCR UNILATERAL SET-UP Verifies integrity of Pudendal Nerve Unilaterally Recorded from Bilateral Sphincter Response typically stronger on side of Stimulation Electrode Placement Recording Electrodes Anal Sphincter Muscle =Cathode =Anode = Electrodes can be placed either hemisphincter or bilaterally; discussed later in PPT 8

9 PUDENDAL NERVE MONITORING: BCR PARAMETERS Stimulation Parameters Recording from Dorsal Nerve Stimulation Monophasic Constant Current 5-30mA 0.1msec duration from 0.2-2Hz Train Stimuli 4 (1Hz) Pulses, Pulse Duration 0.5ms Recording Parameters: Filters: LFF 2-30Hz HFF- 1,000-3,000Hz IPI 3ms Double train Stimuli msec ITI PUDENDAL NERVE MONITORING: BCR Unilateral Stimulation activating Bilateral BCR Response Note: Smaller Response on Left to Right Sided Unilateral Stimulation Note: Initial Response after First Train and Polysynaptic Response after 2 nd Train Stimulation PUDENDAL NERVE MONITORING: BCR BCR Change Intraoperatively: Low Amplitude Response on Right 9

10 PUDENDAL NERVE BCR TECHNIQUES Skinner and Vodusek, 2014 Amplitudes were significantly higher when a hemi-sphincter needle was referred to a distant reference Compared to paired needles 1-2cm apart in each hemisphincter In one study with unilateral recording only BCR was recorded in 57/70 (81%) in Men BCR was Recorded in 3/24 (13% in Women Recording only from hemisphincter Another Recent Study 100 patients (60 female; 40 Men) Double Train Stimuli BCR Recording 86/100 with 2/2 hemisphincter recording BCR recording 8/100 with 1/.2 hemisphincter recording BCR Recording 6/100 with 0/2 Hemisphincter recording Recordings unobtainable due to dislodge stim electrodes; Pre-op LMN Pathology, and questionable neurogenic bladder dysfunction PUDENDAL NERVE BCR ALARM CRITERIA No settled alarm criteria When anesthesia and perfusion remains constant: Disappearance of response should be regarded as an alarm Especially when associated with risky surgical process Diminished waveform Complexity May forewarn that signal disappearance imminent May indicate incomplete block within reflex circuit Suggest Reporting to Surgeon Like MEP s Occasional False Positives of lost BCR are inevitable PUDENDAL NERVE MAPPING: WHAT ROOTS? Distribution of Pudendal Nerve Fibers are referenced to Nerve Roots S2, S3, and S4 18% of patients found to have Pudendal Nerve afferents in Single Segmental Level 7% of individuals one single dorsal root on one aside was found to carry all pudendal afferents Therefore, injury to that single root could result in significant pudendal afferent dysfunction and loss of sphincter function Becomes even more challenging in patients with cerebral palsy and spasticity with unevenly distributed nerve roots. Mapping of Sensory Nerve Roots may be essential to protection of the pudendal nerve 10

11 PUDENDAL NEUROGRAM SACRAL ROOT SENSORY NERVE ACTION POTENTIALS Involves mapping the sensory roots of the cauda equina Mapping out Rootlets demonstrating sensory function and sparing these rootlets may assist in: Bladder Control Postoperatively Normal Sexual Function in Maturity PUDENDAL NEUROGRAM SACRAL ROOT SENSORY NERVE ACTION POTENTIALS Dorsal Nerve Stimulation 0.2ms Square Wave Pulses Recording Ascending Sensory Volley is recorded from a bipolar probe held by surgeon Roots and Rootlets can be separated out to identify Sacral Roots S1, S2 and S3 100 Averages stimulation delivered through soft tissue PUDENDAL NEUROGRAM SACRAL ROOT SENSORY NERVE ACTION POTENTIALS Case Review 114 Children undergoing Dorsal Rhizotomy for Spacticity in Cerebral Palsy Substantial subset of roots contain NO demonstrable sensory responses by this measure (Huang 1997) Responses vary per subject Recordable responses in all 3 roots in 25% population 1 root level in 18% Less than 50% have symmetrical distributed responses at each level small number 7.6% have recordable potentials in only 1 root of 6. Reported no urinary dyscontrol in 104 patients that this technique could be successfully executed Previous Report (Lang 1994) shows that inclusion of the S2 Roots markedly improved rate of spasticity reduction Utilizing this Neurogram to spare only those with sensory function seems reasonable 11

12 IOM ELECTRODE SELECTION FOR PUDENDAL NERVES Recording Electrodes Silver-Silver Chloride Cup Electrodes Deletis, 1992 Requires Skin Preparation, utilized skin prep gel More preferred for clinical testing Subdermal Needle Electrodes Slimp, 2008 No skin Preparation Stimulating Electrodes Subdermal Needle Electrodes Concerns for iatrogenic injury in males due to vascularity Difficult to Adhere Adhesive Tab Electrodes or Saddle Surface Electrode Cohen, 1991 Requires Skin Preparation, utilized Alcohol ANESTHESIA AND PUDENDAL NERVE MONITORING Mapping for Pudendal Nerve Roots TIVA Optimal No Paralytics SSEP TIVA Optimal Inhalational Anesthetic Under 1 MAC In SSEP s changes to P40 waveform affected similarly to PTN SSEPs BCR TIVA Optimal Difficult to obtain with inhalational agents Better results with double train stim if inhalation agents used No Paralytic SURGERIES WHERE PUDENDAL NERVE MONITORING CAN BE UTILIZED Orthopedic Surgeries S1 or below Cauda equina syndrome Tethered Cord Surgeries of the Prostate Nerve Sparing Rhizotomy Surgeries at or near conus medullaris Surgeries where LSEPs are unobtainable by any recording method Any surgery where patient is Experiencing Bowel or Bladder Incontinence as symptom 12

13 REFERENCES Cohen BA, Major MR, Huizenga BA. Pudendal nerve evoked potential monitoring in procedures involving low sacral fixation. Spine 1991;16(suppl 8): S375 S378. Deletis V, Vodusek DB, Abbott R, et al. Intraoperative monitoring of the dorsal sacral roots: minimizing the risk of iatrogenic micturition disorders. Neurosurgery 1992;30: Kothbauer KF, Novak K. Intraoperative monitoring for tethered cord surgery: an update. Neurosurg Focus 2004;16:E8. Lang FF, Deletis D, Cohen HW, et al. Inclusion of the S2 dorsal rootlets in functional posterior rhizotomy for spasticity in children with cerebral palsy. Neurosurgery 1994;34: Opsomer RJ, Guerit JM, Wese FX, van Cangh PJ. Pudendal cortical somatosensory evoked potentials. J Urol 1986;135: Slimp J. Somatosensory evoked potential monitoring with dermatomal stimulation. In: Nuwer MR, ed. Intraoperative monitoring of neural function: handbook of clinical neurophysiology. Amsterdam: Elsevier, 2008;8: Vodusek DB. Pudendal SEP and bulbocavernosus reflex in women. Electroencephalogr Clin Neurophysiol 1990;77: Vodusek DB, Deletis V. Sacral roots and nerves, and monitoring for neurologic procedures. In: Nuwer MR, ed. Intraoperative monitoring of neural function: handbook of clinical neurophysiology. Amsterdam: Elsevier, 2008;8: