Intraoperative Neuromonitoring in Surgery of Cauda Equina and Conus Medullaris Tumors.

AIM: To demonstrate the value of special intraoperative neuromonitoring techniques for cauda equina and conus medullaris tumors (CECMT) by describing standard methods used at our center. MATERIAL AND METHODS: Neurophysiological records were retrospectively reviewed for 16 patients (eight females and eight males; age range: 27â€"60 years) who underwent surgery for CECMT at our department between 2016 and 2018. RESULTS: Motor and/or sensorial deficits were preoperatively identified in 10 patients; no patients had bladder or sexual dysfunction. Motor evoked potential (MEP) loss occurred in seven patients with full or partial recovery. No changes were seen in pudendal somatosensory evoked potential (SEP) or bulbocavernosus reflex (BCR), and morphological deterioration and amplitude loss of tibial SEPs were present in four patients. Postoperatively, no new neurological deficits and/or bladder and sexual dysfunction were present. CONCLUSION: Pudendal SEP and BCR are useful tests for monitoring CECMT surgeries. BCR is an easily obtainable modality for preserving sacral functions and recommended as a primary monitoring modality in conjunction with traditional neurophysiological techniques during CECMT surgery.

Electric field stimulation induced neuronal differentiation of filum terminale derived neural progenitor cells.

Adult filum terminale (FT) is an atypical region from where multipotent neural progenitor cells (NPCs) have been isolated. However, poor neuronal differentiation rate of FT-NPCs currently limits their clinical applications. Using custom-designed electric fields (EFs), this study sets up a method to significantly improve neuronal differentiation rate of rat FT-NPCs in vitro. We investigated the influence of EF strength on rat FT-NPCs differentiation. By adding reasonable strength of EF to FT-NPCs, our data shows a significant increase in neuronal differentiation rate. The present innovation provides a novel method of directional differentiation and efficient production of neurons from FT-NPCs in vitro. This improved approach for inducing neuronal differentiation can be applied to future research on autoplastic transplantation.

Magnetic resonance imaging assessment of spinal cord and cauda equina motion in supine patients with spinal metastases planned for spine stereotactic body radiation therapy.

PURPOSE: To assess motion of the spinal cord and cauda equina, which are critical neural tissues (CNT), which is important when evaluating the planning organ-at-risk margin required for stereotactic body radiation therapy. METHODS AND MATERIALS: We analyzed CNT motion in 65 patients with spinal metastases (11 cervical, 39 thoracic, and 24 lumbar spinal segments) in the supine position using dynamic axial and sagittal magnetic resonance imaging (dMRI, 3T Verio, Siemens) over a 137-second interval. Motion was segregated according to physiologic cardiorespiratory oscillatory motion (characterized by the average root mean square deviation) and random bulk shifts associated with gross patient motion (characterized by the range). Displacement was evaluated in the anteroposterior (AP), lateral (LR), and superior-inferior (SI) directions by use of a correlation coefficient template matching algorithm, with quantification of random motion measure error over 3 separate trials. Statistical significance was defined according to P<.05. RESULTS: In the AP, LR, and SI directions, significant oscillatory motion was observed in 39.2%, 35.1%, and 10.8% of spinal segments, respectively, and significant bulk motions in all cases. The median oscillatory CNT motions in the AP, LR, and SI directions were 0.16 mm, 0.17 mm, and 0.44 mm, respectively, and the maximal statistically significant oscillatory motions were 0.39 mm, 0.41 mm, and 0.77 mm, respectively. The median bulk displacements in the AP, LR, and SI directions were 0.51 mm, 0.59 mm, and 0.66 mm, and the maximal statistically significant displacements were 2.21 mm, 2.87 mm, and 3.90 mm, respectively. In the AP, LR, and SI directions, bulk displacements were greater than 1.5 mm in 5.4%, 9.0%, and 14.9% of spinal segments, respectively. No significant differences in axial motion were observed according to cord level or cauda equina. CONCLUSIONS: Oscillatory CNT motion was observed to be relatively minor. Our results support the importance of controlling bulk patient motion and the practice of applying a planning organ-at-risk margin.

The postnatal human filum terminale is a source of autologous multipotent neurospheres capable of generating motor neurons.

BACKGROUND: Neural progenitor cells (NPCs) are undifferentiated and mitotic and can be induced to differentiate into neurons and glia, the building blocks of the nervous system. NPCs have great therapeutic potential for nervous system trauma and degenerative disorders. They have been identified in the mammalian central nervous system, but current sources are difficult to access surgically and come from regions that are critical for normal brain function. OBJECTIVE: To identify and characterize in detail a novel source of human NPCs in the filum terminale (FT), a vestigial structure at the caudal end of the spinal cord, which is easily accessed and plays no functional role in the postnatal nervous system. METHODS: Cells were isolated and cultured in vitro from the FT of terminated fetuses and from children and adolescents who had undergone surgical resections for tethered spinal cords. Cell culture techniques, immunohistochemistry, and immunocytochemistry were applied to examine FT cells. RESULTS: : FT cells gave rise to neurospheres that proliferated over extended periods of time in culture. These neurospheres were positive for neural stem/progenitor cell markers by immunocytochemical staining. The neurospheres were able to be induced to differentiate in vitro into neurons and glial cells, which were confirmed by the use of antibodies against the cell type-specific markers. Moreover, they have been induced to form motor neurons capable of innervating striated muscle in vitro. CONCLUSION: Multipotent NPC cells from the FT are both accessible and expendable. They may allow autologous cell-based transplantation therapy that circumvents immunological rejection.

Paraneoplastic lower motor neuronopathy associated with Hodgkin lymphoma.

INTRODUCTION: Paraneoplastic lower motor neuronopathies have been reported rarely with Hodgkin lymphoma. METHODS: We report a case of rapidly progressive motor neuronopathy preceding the diagnosis of Hodgkin lymphoma. RESULTS: A 31-year-old woman developed subacute rapidly progressive quadriparesis. Electrodiagnostic studies revealed a severe diffuse disorder of motor neurons and their axons. Symmetric enhancement of the cauda equina motor nerve roots was notable on magnetic resonance imaging scan. Further imaging demonstrated an enlarged supraclavicular lymph node, and biopsy revealed Hodgkin lymphoma. A final diagnosis of paraneoplastic motor neuronopathy was made after investigations for alternative causes of motor neuronopathy were unrevealing. Neurological improvement was seen with combined treatment of the underlying malignancy and intravenous immunoglobulin. CONCLUSIONS: Paraneoplastic causes should be considered in the differential diagnosis of subacute motor neuronopathy, as the neurological presentation may precede cancer detection. Combinations of lymphoma treatment and immunotherapy may result in a favorable outcome.

Neurophysiologic monitoring in neurosurgery.

This article focuses on the application of neurophysiologic monitoring in uniquely neurosurgical procedures. Neurophysiologic monitoring provides functional testing and mapping to identify neural structures. Once identified, the functionality of the central and peripheral nervous system areas at risk for neurosurgical injury can be monitored. It discusses the use of motor-evoked potentials, sensory evoked potentials, electromyography and electroencephalography to assess neurologic change.

Conductive neuromagnetic fields in the lumbar spinal canal.

OBJECTIVE: To measure neuromagnetic evoked fields in the lumbar spinal canal. METHODS: Using a newly developed superconducting quantum interference device (SQUID) fluxmeter, neuromagnetic fields of 5 healthy male volunteers were measured at the surface of the lower back after stimulation of the tibial nerves at the ankles. For validation, we inserted a catheter-type electrode percutaneously in the lumbar epidural space in 2 of the subjects and measured cauda equina action potentials after tibial nerve stimulation. RESULTS: Neuromagnetic fields propagating from the intervertebral foramina into the spinal canal were measured, and the latencies of the magnetic fields corresponded largely with those of the cauda equina action potentials. CONCLUSIONS: We successfully measured ascending neuromagnetic fields originating at the nerve root and the cauda equina with high spatial resolution. Future studies will determine whether neuromagnetic field measurement of the lumbar spine can be a useful diagnostic method for the identification of the disordered site in spinal nerves. SIGNIFICANCE: We successfully measured neuromagnetic fields in the lumbar spinal canal, which have previously been difficult to verify. Future studies will determine whether neuromagnetic field measurement of the lumbar spine can be a useful diagnostic method for identifying disorders of spinal nerves.

Sacral nerve function in patients with soiling more than 10 years after low anterior resection for lower rectal cancer.

BACKGROUND/AIMS: To assess the neurological function of the puborectalis muscles (PM) in patients with or without soiling after low anterior resection (LAR) for lower rectal cancer, we examined the sacral nerve terminal motor latency (SNTML) of the PM. METHODOLOGY: The latency of the response in the PM following transcutaneous magnetic stimulation of the cauda equina at the levels from S3 to S4 by SNTML was measured in 24 patients after LAR. They were divided into a group with soiling (10 cases; 8 men and 2 women, aged 55 to 70 years with a mean age of 61.6 years) and one without soiling (14 cases; 10 men and 4 women, aged 50 to 69 years with a mean age of 60.3 years), and results were compared with data obtained from 25 control subjects (16 men and 9 women, aged 48 to 71 years with a mean age of 62.1 years). Postoperative monitoring of patients was initiated after a period of more than 10 years (121-144 months; mean: 128.2 months). RESULTS: 1) Distance of anastomosis from the dentate line measured with rectoscopy: Patients with and without soiling registered respective coloproctostomy distances of 2.5 +/- 0.6 (2-3.8) and 5.1 +/- 1.2 (3.0-6.5) cm, with the former showing a tendency (p < 0.0001) toward shorter distances. 2) Values of the SNTML: Patients with soiling (6.9 +/- 2.1 ms) exhibited significant extensions compared with patients without soiling (4.2 +/- 0.6 ms), and control subjects (3.9 +/- 0.6ms) (p < 0.0001, respectively). Moreover, patients without soiling showed more extended SNTML than control subjects at all sites. The conduction delay of SNTML in the patients with soiling was longest, followed by that in those without any soiling, then that in the control subjects. CONCLUSIONS: Soiling after LAR may be caused by damage to the sacral motor nerves.

Magnetic stimulation of the cauda equina in the spinal canal with a flat, large round coil.

Magnetic round coil stimulation over the spinal enlargement activates the spinal nerves at the neuro-foramina level. However, activation of the cauda equina in the spinal canal has never been described in the literature. This study, for which 40 healthy subjects were recruited, activated the cauda equina using a round 20-cm-diameter coil designated as a Magnetic Augmented Translumbosacral Stimulation (MATS) coil. Magnetic stimulation placing the edge of the coil over the L1 and L3 spinous processes elicited compound muscle action potentials (CMAPs) from the abductor hallucis muscle. The CMAPs were compared with those elicited through high-voltage electrical stimulation. The CMAP latencies to L1 level MATS coil stimulation were not significantly different from those evoked by electrical stimulation at the same level. The CMAP latencies to L3 level MATS coil stimulation were varied in each subject. In fact, the L1 level MATS coil stimulation is considered to activate the cauda equina at the root exit site from the conus medullaris; the L3 level MATS coil stimulation activates some mid-part of the cauda equina or the distal cauda equina by spreading current. The MATS coil facilitates evaluation of spinal nerve conduction in the cauda equina.

Saddle sensation is preserved in a few patients with cauda equina or conus medullaris lesions.

Although saddle sensory deficit seems the most useful clinical sign in the diagnosis of a cauda equina or conus medullaris lesion, findings of previous studies were controversial. The aim of the present study was to try to resolve this issue. The data from the author's series of patients with clinical, electrodiagnostic and radiological findings compatible with a cauda equina lesion were reviewed. Of the 117 patients in the series, 11 (10 men) did not have a saddle sensory deficit. These 11 patients had less severe sacral dysfunction than the others, and none of them needed urgent surgical intervention. They all had electromyographic (EMG) signs of a significant motor fibre lesion, and in seven men the sacral (penilo-cavernosus) reflex was clinically abnormal. The study revealed normal saddle sensation in approximately 10% of patients with cauda equina or conus medullaris lesions. Dissociation between preserved touch sensation and abnormal EMG findings, as well as dissociation between preserved touch sensation and a non-elicitable penilo-cavernosus reflex might be explained by preservation of the thinner sensory nerve fibres, which are more resistant to compression. Although, saddle sensory loss seems to identify patients who might benefit from urgent spinal imaging and surgery, further diagnostic evaluation is also indicated in patients with normal saddle sensation, particularly due to the increased frequency of spinal tumours found in this subgroup.

The effect of cauda equina constriction on nitric oxide synthase activity.

Nitric oxide synthase (NOS) activity was studied in the gray and white matter regions of the spinal cord 2 and 5 days after multiple cauda equina constrictions of the central processes of L7-Co5 dorsal root ganglia neurons. The results show considerable differences in enzyme activity in the thoracic, upper lumbar, lower lumbar, and sacral segments. Increased NOS activity was observed at 2 days after multiple cauda equina constrictions in the dorsal, lateral, and ventral columns of the lower lumbar segments and in the ventral column of the upper lumbar segments. The values returned to control levels within 5 postconstriction days. In the lateral columns of thoracic segments taken 2 and 5 days after surgery, NOS activity was enhanced by 54% and 55% and in the upper lumbar segments by 130% and 163%, respectively. Multiple cauda equina constrictions performed surgically for 2 and 5 days caused a significant increase in NOS activity predominantly in the gray matter regions of thoracic segments. A quite different response was found 5 days postconstriction in the upper lumbar segments, where the enzyme activity was significantly decreased in the dorsal horn, intermediate zone, and ventral horn. No such extreme differences could be seen in the lower lumbar segments, where NOS activity was significantly enhanced only in the ventral horn. The data correspond with a higher number of NOS immunoreactive somata, quantitatively evaluated in the ventral horn of the lower lumbar segments at 5 days after multiple cauda equina constrictions. While the great region-dependent heterogeneity in NOS activity seen 2 and 5 days after multiple cauda equina constrictions is quite apparent and suggestive of an active role played by nitric oxide in neuroprotective or neurotoxic processes occurring in the gray and white matter of the spinal cord, the extent of damage or the degree of neuroprotection caused by nitric oxide in compartmentalized gray and white matter in this experimental paradigm would be possible only using longer postconstriction periods.

Intraoperative urodynamics in spinal cord surgery: a study of feasibility.

Intraoperative monitoring (IOM) of bladder function in spinal cord surgery is a challenging task due to vegetative influences, multilevel innervation and numerous supraspinal modulating factors. Despite routine use of urodynamics in neurosurgery for implantation of bladder stimulators or denervation of nerve fibres in spastic reflex bladders, application of IOM in patients with spinal cord tumours or tethered-cord syndrome is not widespread. Combining urodynamics with sphincter electromyography (EMG) in IOM enables identification of bladder efferents responsible for contraction and continence. We monitored four patients with ependymoma of the Cauda equina, one patient with tethered-cord syndrome and two patients with cervical intramedullary tumours. In all patients undergoing operations of the Cauda equina, identification of bladder efferents responsible for detrusor contraction was possible. There was good correlation between preoperative bladder dysfunction, preoperative urodynamics and intraoperative pressure increase by bladder contraction or latency between stimulation and contraction. This method proved unsuitable for intramedullary tumours where no contraction of the bladder could be observed while stimulating the spinal cord. Intraoperative monitoring of urodynamics is an effective tool for identifying bladder efferents in the Cauda equina. Intraoperative conclusions on bladder dysfunction through registration of pressure increase and latency are possible.

[Magnetoneurographic registration of evoked summation action fields over lumbar vertebrae following transcutaneous tibial nerve stimulation]. / Magnetoneurographische Darstellung evozierter Summenaktionsfelder über der lumbalen Wirbelsäule nach transkutaner N. Tibialis Stimulation.

Goal of this study was the development of a protocol for the registration of evoked magnetic fields over the lumbar spine using off-the-shelf equipment. Three subjects in a sitting position with their torso bent slightly forward were stimulated at the tibial nerve with a commercially available stimulator. Neuromagnetic fields were registered over a circular, 800 cm2 area of the lumbosacral spine using a 61-channel 4D-Neuroimaging biomagnetometer. After appropriate signal processing, dipolar magnetic fields with a field strength 5-17 fT peak-to-peak amplitude were detected in three out of four registrations. Location and orientation of these fields concurred with the expected evoked compound action currents along the course of the nerve fibers.

Cauda equina syndrome.

Single or double-level compression of the lumbosacral nerve roots located in the dural sac results in a polyradicular symptomatology clinically diagnosed as cauda equina syndrome. The cauda equina nerve roots provide the sensory and motor innervation of most of the lower extremities, the pelvic floor and the sphincters. Therefore, in a fully developed cauda equina syndrome, multiple signs of sensory disorders may appear. These disorders include low-back pain, saddle anesthesia, bilateral sciatica, then motor weakness of the lower extremities or chronic paraplegia and, bladder dysfunction. Multiple etiologies can cause the cauda equina syndrome. Among them, non-neoplastic compressive etiologies such as herniated lumbosacral discs and spinal stenosis and spinal neoplasms play a significant role in the development of the cauda equina syndrome. Non-compressive etiologies of the cauda equina syndrome include ischemic insults, inflammatory conditions, spinal arachnoiditis and other infectious etiologies. The use of canine, porcine and rat models mimicking the cauda equina syndrome enabled discovery of the effects of the compression on nerve root neural and vascular anatomy, the impairment of impulse propagation and the changes of the neurotransmitters in the spinal cord after compression of cauda equina. The involvement of intrinsic spinal cord neurons in the compression-induced cauda equina syndrome includes anterograde, retrograde and transneuronal degeneration in the lumbosacral segments. Prominent changes of NADPH diaphorase exhibiting, Fos-like immunoreactive and heat shock protein HSP72 were detected in the lumbosacral segments in a short-and long-lasting compression of the cauda equina in the dog. Developments in the diagnosis and treatment of patients with back pain, sciatica and with a herniated lumbar disc are mentioned, including many treatment options available.

Effects of unilateral suckling on nursing behavior and c-fos activity in the caudal periaqueductal gray in rats.

In rats, suckling elicits kyphosis-the bilaterally symmetrical, upright, humpbacked nursing posture-and maximal expression of the immediate early gene c-fos in a region of the caudal periaqueductal gray (cPAG) that mediates the sensorimotor integration of kyphosis. We determined the effects of prepartum unilateral nipple removal on nursing behavior and c-fos expression during a 60-min mother-litter interaction on Day 7 postpartum. Compared with dams suckled by 6 pups bilaterally, dams suckled unilaterally displayed essentially normal maternal behaviors, including kyphosis. Unilaterally suckled dams, however, showed an increase in the abnormal prone nursing posture, a decrease in proportion of kyphotic nursing of total time over pups, and a 20% higher contralateral/ipsilateral ratio of cPAG neurons expressing c-fos. These results are consistent with an incompletely lateralized neural pathway conveying suckling stimulation to the cPAG and provide a mechanism whereby kyphosis is elicited by unilateral suckling when pups initiate nursing from their supine dam.

[Intraoperative electrophysiological monitoring for functional preservation of the cauda equina during lumbosacral surgery].

Adequate electrophysiological techniques to monitor function of the cauda equina have been proposed for surgery in patients with lumbosacral lipoma or myeloschisis. Motor fibers were identified by electrical stimulation in the operating field with bipolar rectangular impulses of 200 mu sec duration at 2 Hz under 5 mA and compound muscle action potentials (CMAPs) recorded from the leg and anal muscles. By recording CMAPs from the tibialis anterior, the biceps femoris, the gastrocnemius, and the external anal sphincter muscles, all of the roots from the fourth lumbar to the fourth sacral segment were continuously monitored. To spare recording channels, recordings were obtained from the right versus the left side. In our institute, 5 patients have undergone lumbosacral surgery while using this monitoring system, and the results indicated that there was no postoperative neurological exacerbation in any of the cases. According to a combination of the CMAPs produced by stimulation, the segment of the stimulated motor root could be identified electrophysiologically. Monitoring of somatosensory evoked potentials was not performed because this would have required too much time and would have prolonged surgery. However, some sensory fibers, which appeared to be posterior roots of the cauda equina on intraoperative inspection, could be identified indirectly with CMAPs recording because of current spreading from the stimulation to motor fibers.

Tumor necrosis factor alpha and nucleus-pulposus-induced nerve root injury.

STUDY DESIGN: The effects of nucleus pulposus and various treatments to block tumor necrosis factor alpha activity were evaluated in an experimental set-up using immunohistochemistry and nerve conduction velocity recordings. OBJECTIVES: To assess the presence of tumor necrosis factor alpha in pig nucleus pulposus cells, and to see if block of tumor necrosis factor alpha also blocks the nucleus-pulposus-induced reduction of nerve root conduction velocity. SUMMARY AND BACKGROUND DATA: A meta-analysis of observed effects induced by nucleus pulposus revealed that these effects might relate to one specific cytokine-tumor necrosis factor alpha. METHODS: Series-1: Cultured nucleus pulposus cells were stained immunohistologically with a monoclonal antibody for tumor necrosis factor alpha. Series-2: Nucleus pulposus was harvested from lumbar discs and applied to the sacrococcygeal cauda equina in 13 pigs autologously. Four pigs received 100 mg of doxycycline intravenously; five pigs had a blocking monoclonal antibody to tumor necrosis factor alpha applied locally in the nucleus pulposus, and four pigs remained nontreated, forming a control group. Three days after the application, the nerve root conduction velocity was determined over the application zone by local electrical stimulation. RESULTS: Series-1: Tumor necrosis factor alpha was found to be present in the nucleus pulposus cells. Series-2: The selective antibody to tumor necrosis factor alpha limited the reduction of nerve conduction velocity, although in comparison with the control group this was not statistically significant. However, treatment with doxycycline significantly blocked the nucleus-pulposus-induced reduction of conduction velocity. CONCLUSION: For the first time, a specific substance, tumor necrosis factor alpha, has been linked to the nucleus-pulposus-induced effects of nerve roots after local application. Although the effects of this substance may be synergistic with those of other similar substances, the data of the current study may be of significant importance for the continued understanding of nucleus pulposus' biologic activity, and of possible potential use for future strategies in managing sciatica.

Somatosensory evoked potentials recorded from the posterior pharynx to stimulation of the median nerve and cauda equina.

Somatosensory evoked potentials (ppSEPs) in response to stimulation of the median nerve at the wrist and the cauda equina at the epidural space (the L4 level) were recorded from the posterior wall of the pharynx in 15 patients who underwent spinal surgery under general anesthesia, using disc electrodes attached to the endotracheal tube, and compared with segmental spinal cord potentials (seg-SCPs) that were recorded simultaneously from the posterior epidural space (PES). ppSEPs consisted of the initially positive spike (P9) followed by slow positive (P13) and negative (N22) waves. The P13 and N22 of ppSEPs had phase reversal relationship with the P2 and N2 recorded from the PES, respectively. The peak latencies of P9 (9.40 +/- 0.7 ms) (mean +/- SD), P13 (13.1 +/- 0.9 ms), and N22 (22.0 +/- 2.1 ms) of ppSEPs coincided with those of P1, N1 and P2 of seg-SCPs, respectively, ppSEPs were recorded more clearly with a reference electrode on the dorsal surface of the neck than with the reference electrode at the earlobe or back of the hand. The threshold and maximal stimulus intensities were also similar between the ppSEPs and seg-SCPs. Thus, the P9, P13, and N22 components of ppSEPs were thought to have the same origin as the P1, N1 and P2 of seg-SCPs, respectively. Therefore, the P9, P13 and N22 of ppSEPs may reflect incoming volleys through the root, synchronized activities of the interneurons and primary afferent depolarizations (PAD), respectively. ppSEPs in response to cauda equina stimulation showed that the latencies of the two initial components (4.6 +/- 0.4 and 6.4 +/- 0.6 ms) corresponded to those of the SCPs recorded from the PES (4.6 +/- 0.3 and 6.3 +/- 0.5 ms), suggesting that these potentials reflect impulses conducting through the spinal cord, similar to epidurally recorded SCPs.

A new method using neuromagnetic stimulation to measure conduction time within the cauda equina.

Using principles derived from electric field measurements and studies of phrenic nerve in vitro, neuromagnetic stimuli in humans were predicted to excite selective low threshold sites in proximal and distal cauda equina. Physical models, in which induced electric fields were recorded in a segment of human lumbosacral spine immersed in a saline filled tank, supported this prediction. Conclusions from the model were tested and confirmed in normal human subjects. Ipsilateral motor evoked potentials were elicited in lower limb muscles and striated sphincters by magnetic coil (MC) stimulation of both proximal and distal cauda equina. Over proximal cauda equina a vertically oriented MC junction and cranially directed induced current elicited a newly identified compound muscle action potential (CMAP). The F response latency and lack of attenuation when the target muscle was vibrated suggest that the proximal response is a directly elicited M response arising near or at the rootlet exit zone of the conus medullaris. Over distal cauda equina, lumbar roots were optimally excited by a horizontally oriented MC junction, and sacral roots by an approximately vertically oriented MC junction, eliciting CMAPs with similar appearance but shorter latency consistent with the known intrathecal lengths of the lower lumbar and sacral nerve roots. The induced current was usually most effective when directed towards the spinal fluid filled thecal sac. Normal subjects showed stable CMAP onset latencies elicited at proximal and distal cauda equina despite wide variation in amplitude. Thus, cauda equina conduction time can be directly calculated. This new method may improve the detection and classification of peripheral neuropathies affecting lower limbs and striated sphincters.