Glycerol neurolysis: neurophysiological effects of topical glycerol application on rat saphenous nerve

Agents Used for Nerve Blocks and Neurolysis

The recognition of pain and the treatments used for it are vital for all practitioners. Many types of pain can be treated in a locoregional fashion, which has significant implications not just for any individual patient but for society as a whole. These treatments are most effective when performed in a minimally invasive, image-guided fashion. Interventional radiologists should play a central role in providing these lifestyle-limiting treatments. This article describes the medications most typically used for spinal and extra-axial treatments in the management of patients in pain.

An experimental animal model for percutaneous procedures used in trigeminal neuralgia

OBJECT

This study describes an experimental rabbit model that allows the reproduction of percutaneous operations that are used in patients with trigeminal neuralgia (TN). Attention was given to an exact anatomical description of the rabbit's middle cranial fossa as well as the establishment of conditions for a successful procedure.

METHODS

Morphometric measurements were taken from 20 rabbit skulls and CT scans. The anatomy of the trigeminal nerve, as well as its surrounding structures, was assessed by bilateral dissection of 13 New Zealand white rabbits (NWR). An ideal approach of placing a needle through the foramen ovale to reach the TG was sought. Validation of correct placement was realized by fluoroscopy and confirmed by dissection.

RESULTS

Precise instructions for successful reproduction of percutaneous procedures in NWR were described. According to morphological measurements, for balloon compression of the trigeminal ganglion (TG) the maximal diameter of an introducing cannula is 1.85 mm. The diameter of an empty balloon catheter should not exceed 1.19 mm, and the length of the inflatable part of the balloon can range up to 4 mm. For thermocoagulation the needle electrodes must not exceed an external diameter of 1.39, mm and the length of the non-insolated tip can range up to 4 mm. Glycerol rhizolysis can be achieved because the trigeminal cistern in the NWR is a closed space that allows a long dwelling time (>10 min) of the contrast agent.

CONCLUSIONS

An experimental NWR model intended for the reproduction of percutaneous procedures on the TG has been meticulously described. This provides a tool that enables further standardized animal research in the field of surgical treatment of TN.

Percutaneous treatments for trigeminal neuralgia

Trigeminal neuralgia (TN) is a neurologic disorder, defined by paroxysmal electric shocklike painful attacks in 1 or more trigeminal nerve branches. Treatment of TN is diverse and includes minimally invasive percutaneous techniques, which consist of balloon compression, glycerol rhizotomy, and radiofrequency thermocoagulation. Although all 3 techniques are generally safe, efficient, and effective, a clear consensus has not been reached regarding their specific indications and degree of efficacy. The aim of this article is to describe the percutaneous treatments available for TN and outline their characteristics, technique, indications and efficacy.

Dose-dependent toxicity of a commercially available demineralized bone matrix material

STUDY DESIGN

A relative risk assessment was performed to determine the safety of three commercially available Grafton demineralized bone matrix quantities used in athymic rats.

OBJECTIVE

To evaluate the possible dose-dependent adverse effects of a commercially available demineralized bone matrix containing glycerol.

SUMMARY OF BACKGROUND DATA

Commercially available Grafton demineralized bone matrix contains glycerol. The toxic effects of glycerol leading to acute renal failure have been documented. The toxicity of this glycerol-containing substance in higher doses has not been reported.

METHODS

Three doses of Grafton putty were implanted in the upper hind limb muscles of athymic nude rats. The rats were observed for adverse effects and early death. Histologic studies were performed.

RESULTS

All eight of the rats implanted with the highest dose of Grafton putty (0.008 mL/g) died, five of them within 12 hours of implantation and three in 48 to 72 hours. One rat with the intermediate dose (0.004 mL/g) died within 12 hours of implantation. By 72 hours after implantation, three of the six rats (50%) with the intermediate dose had died. All six of the rats receiving the lowest dose (0.002cc/g) survived. The median lethal dose of Grafton putty in athymic rats was estimated to be 0.00469 mL/g body weight. Histologic analysis of the animals that received the high dose showed acute tubular necrosis, probably secondary to rhabdomyolysis.

CONCLUSIONS

In athymic rats, large amounts of Grafton putty lead to death in a dose-dependent manner. Because the median lethal doses of Grafton putty (0.00469 mL/g) and glycerol (0.00442 mL/g) are comparable, a potential source of toxicity is the glycerol contained in the material. The results of this study suggest that high doses have the potential to cause acute renal failure. The authors suggest that clinical usage of Grafton putty in humans should be limited to no more than 2 mL/kg body weight of this material.

Indications and Technique of Thoracic(2) and Thoracic(3 )Neurolysis

This article reviews the technique of thoracic (T)(2) and T(3) sympathetic ganglion block and neurolysis. Historic aspects of this technique are described. The concept of radiofrequency thermocoagulation (RFTC) of T(2) and T(3) is discussed and the technique is detailed. This procedure is useful for complex regional pain syndrome (CRPS), vascular compromise, and neuropathic pain syndromes of upper extremities. It is an alternative to stellate ganglion ablation and may be useful for patients with sympathetically maintained pain who have persistent pain after stellate ganglion procedures.

Relief of trigeminal neuralgia after percutaneous retrogasserian glycerol rhizolysis is dependent on normalization of abnormal temporal summation of pain, without general impairment of sensory perception

OBJECTIVE

This study was undertaken to examine the pathophysiological mechanisms of trigeminal neuralgia and the mechanisms underlying pain relief after percutaneous retrogasserian glycerol rhizolysis (PRGR).

METHODS

Quantitative examination of sensory and pain perception was performed in the trigger area and the contralateral nonpainful facial skin area for 39 patients with trigeminal neuralgia who had been previously treated with PRGR and for 14 non-surgically treated patients. In a prospective study, 9 of the 14 patients were examined before and 4 to 6 weeks after PRGR.

RESULTS

In the trigger area of patients who had been previously treated with PRGR for trigeminal neuralgia, we demonstrated increased temperature and tactile thresholds in pain-free patients and in patients with paroxysmal or continuous pain. Abnormal temporal summation of pain (characterized by progressive increases in pain intensity, with radiation of pain and aftersensation) was present in patients with paroxysmal or continuous pain but not in pain-free patients. In the trigger area of non-surgically treated patients with trigeminal neuralgia, we demonstrated significantly increased temperature and tactile thresholds and the presence of abnormal temporal summation of pain. The prospective study showed that pain relief after PRGR was associated with normalization of abnormal temporal summation of pain, without increased sensory loss.

CONCLUSION

Partial deafferentation, with impairment of thin (C/Adelta) and thick (Abeta) fiber-mediated sensations and abnormal temporal summation of pain, is present in the trigger area of patients with trigeminal neuralgia. Relief of pain after PRGR depends on the normalization of abnormal temporal summation of pain, which is independent of general impairment of sensory perception. Assessment of the temporal summation of pain may serve as an important tool to record central neuronal hyperexcitability, which may play a key role in the pathophysiological changes in trigeminal neuralgia.

Influence of previous treatment on outcome after glycerol rhizotomy for trigeminal neuralgia

The aim of the present study was to evaluate the influence of previous treatment on outcome and sensory disturbance after a retrogasserian glycerol injection for trigeminal neuralgia. Ninety-nine patients with trigeminal neuralgia underwent a retrogasserian glycerol rhizotomy. Fifty-three of those patients experienced recurrent pain after the previous treatment. At the 1 year follow-up, the outcome was excellent or good in 83% of patients with no previous treatment, compared with 60 and 75% in those patients with earlier glycerol injections or radiofrequency lesions, respectively. Quantitatively assessed, the sensory impairment was most pronounced in patients who had earlier radio-frequency lesions compared with patients not treated previously. The occurrence of dysesthesia was more frequent in patients who had been surgically treated earlier. A review of the literature showed that the concentration of the glycerol preparation used probably is of great importance in terms of pain relief and sensory sequelae.

Glycerol injection into the trigeminal ganglion provokes a selective increase in human cerebral blood flow

Fourteen patients suffering from idiopathic trigeminal neuralgia (refractory to medication) were treated by injection of glycerol into the trigeminal ganglion. The changes in cerebral blood flow (CBF) after glycerol injection were quantified by intravenous 133Xe emission tomography. There was a significant 11% (P less than 0.01) increase in ipsilateral CBF and an 8% (P less than 0.05) increase in contralateral CBF 1 h after glycerol injection. The interhemispheric difference was significant (P less than 0.05). The increase was significantly greater in the ipsilateral internal carotid territory, in the anterior cerebral artery and middle cerebral artery territories (superficial (P less than 0.05), deep territories (P less than 0.001]. We suggest that these changes are due to the release of substance P and/or calcitonin gene-related peptide, from terminals of the trigeminal-vascular system during glycerol injection.

Ablative neurosurgical procedures for the treatment of chronic pain

This article is devoted to ablative neurosurgical procedures used for the treatment of chronic pain. The authors detail only those procedures that are currently performed. The procedures are classified as those directed to the peripheral nerves, spinal roots and cranial nerves; the dorsal root entry zone; the ascending extra-lemniscal pathways. The authors have analyzed the results of their own series and those published in the literature. They concentrate on the rationale and neurophysiological effects of the operations.

Percutaneous retrogasserian glycerol rhizotomy. Predictors of success and failure in treatment of trigeminal neuralgia

Eighty-five medically intractable trigeminal neuralgia patients treated by percutaneous retrogasserian glycerol rhizotomy (PRGR) were followed for 6 to 54 months. The median time to recurrence of symptoms refractory to medical therapy and requiring further intervention was 3 years (by Kaplan-Meier survival analysis). The median time to recurrence of symptoms requiring some form of medical treatment was 2 years. Following repeat PRGR for recurrent symptoms, the median time to recurrence was 1 year. Univariate log rank statistics and multivariate Cox proportional hazards modeling revealed significant associations between favorable outcome and female sex, absence of atypical features or associated cluster headache symptoms, success of prior carbamazepine therapy, duration of symptoms, and cerebrospinal fluid return during the procedure. A scoring system using prognostic factors has been developed based upon these findings. Assessment of published studies of PRGR and of other treatments for trigeminal neuralgia is made difficult by the variety of outcome measures employed and variable follow-up intervals. The present study attempts to address these issues by definition of endpoints, statistical analysis of the data, and identification of important prognostic factors in a manner useful to the clinician.

Sensory disturbance following percutaneous retrogasserian glycerol rhizotomy

Nineteen patients with tic douloureux were treated with glycerol injection in the trigeminal cistern. Facial sensibility was measured with an electrical stimulator one day before and one day after the glycerol treatment. The thresholds for perception and pain, and the maximal pain tolerance rose by about 50% (p less than 0.01, 0.01, and 0.001, respectively). The hypaesthesia and hypalgesia were most marked just below the eye, whereas the mandibular division showed only slight sensory impairment. In 13 patients a follow-up sensimetry study was done 1-7 months after surgery. Thirteen patients became completely free of pain and one almost completely free from pain (74%). Two had no pain relief. Twelve patients had no subjective complaints of the treatment. Three reported on dysaesthesiae (16%) over the previously painful area. Seven patients (37%) had subjective sensations of diminished or altered sensibility: numbness and hypalgesia in the face. Corneal hypaesthesia was recorded in ten patients (53%). Glycerol has a non-specific neurotoxic effect which is equal for tactile and nociceptive fibres. Sensory impairment may be a conditio sine qua non for a good clinical result.

Percutaneous retrogasserian glycerol rhizolysis in the management of trigeminal neuralgia

Sixty patients with trigeminal neuralgia or atypical facial pain were followed for an average of 1 year after percutaneous retrogasserian glycerol rhizolysis. The procedure was initially effective in relieving pain in 80% of the patients with typical trigeminal neuralgia and symptomatic trigeminal neuralgia secondary to multiple sclerosis. However, life-table analysis indicated that 50% of this group had persistence or recurrence of pain within 18 months after the operation. Percutaneous retrogasserian glycerol rhizolysis was ineffective in relieving atypical trigeminal neuralgia or atypical facial pain. Minor complications occurred in 23% of patients, and major morbidity was seen in 1.6%. Facial sensory loss which persisted for more than 1 month was found in 72% of patients, corneal hypesthesia occurred in 15%, and an additional 7% had corneal anesthesia. The data indicate that the success of percutaneous retrogasserian glycerol rhizolysis in relieving trigeminal neuralgia is directly related to the production of facial sensory loss.

Recurrent trigeminal cistern glycerol injections for tic douloureux

Fourteen of 60 cases (23%) of trigeminal neuralgia underwent a repeat trigeminal cistern glycerol injection for recurrent pain. The mean time to recurrence was 14 months and the mean follow-up time following the last injection 10 months. Measurement of trigeminal cistern volume at the first and second procedure with metrizamide showed a significant decrease in the cistern volume from 0.38 ml to 0.29 ml. Clumping of nerve roots indicative of arachnoiditis was observed in 4 cases. In 2 further cases difficulty was encountered in emptying the cistern of metrizamide. After the repeat injection 2 patients developed painful dysethesia. Six patients showed either new or increased facial sensory deficits. These findings may indicate trigeminal cistern arachnoiditis. The possibility of deafferentation pain developing after trigeminal glycerol rhizolysis should prompt caution in the use of this technique in the younger patient.

Spontaneous activity in afferent and efferent fibers after chronic axotomy: response to potassium channel blockade

Distally propagating spontaneous impulses in acutely and chronically cut rat saphenous nerve were examined to determine (1) the origin(s) of the activity, (2) the fiber types involved, and (3) whether the activity was affected by potassium channel blockade. Under deep pentobarbital anesthesia, six male Sprague-Dawley rats underwent L3 cauda equina section, then unilateral saphenous axotomy. The nerve was then dissected into 30-50 microfilaments and surveyed for spontaneous activity using a modification of the microfilament recording method. Afterward, the nerve was cut back, and a potassium channel blocking agent (gallamine) was administered. The axonal activity was once again surveyed in the same fashion. Twenty-eight rats underwent unilateral saphenous axotomy 1-8 weeks prior to similar recordings, and the neuroma was excised just before microfilament dissection. Spontaneous discharges in these preparations originated from three foci: (1) antidromic activity from in-continuity dorsal root ganglia (DRG), (2) orthodromic activity from sympathetic neurons, and (3) antidromic activation of dichotomizing afferent axons in the peripheral nerve. There was significantly more antidromic activity from DRG in rats with prior axotomies than in control animals (t = 2.38; p less than 0.025), and gallamine produced a significant increase in DRG activity in the chronically lesioned nerve (t = 2.43; p less than 0.005), but not in acutely lesioned controls. However, most of the spontaneous activity in these preparations was from sympathetic efferents. This activity was decreased significantly by chronic axotomy (t = 2.635; p less than 0.01), and it was not affected by potassium channel blockade with gallamine. In two microfilaments, spontaneous antidromic action potentials were observed in conjunction with a clear receptive field on blood vessels in the nearby fascia. Both of these presumably dichotomized axons were found in acutely cut nerve, thus were not the result of retrograde sprouting from a neuroma. It was concluded that (1) chronic axotomy of sensory afferents produced ectopic activity in their respective DRG, (2) gallamine administration increased spontaneous activity from DRG in chronically axotomized rats, (3) ongoing sympathetic efferent activity in rat saphenous nerve was decreased by distal axotomy for up to 8 weeks, and (4) rare branched sensory afferents occasionally exhibit spontaneous activity.

Human trigeminal root evoked potentials during differential retrogasserian thermal and chemical rhizotomy

Human trigeminal root evoked potentials have been recorded using signal averaging techniques during radiofrequency trigeminal rhizotomy and lidocaine blocks in patients with trigeminal neuralgia. Both short and long latency trigeminal root potentials have been recorded which appear to represent fast- and slow-conducting fiber activity respectively. Long latency trigeminal root potentials appear in recordings at the noxious threshold as perceived by the awake patient and are relatively selectively abolished in a reversible fashion by lidocaine block and irreversibly by radiofrequency heat. Evaluation of these trigeminal root potentials provides an objective assessment of the results of pain surgery directed at differential destruction of slow-conducting fiber activity.

Has the amount of spontaneous electrical activity in experimental neuromas been overestimated?

Previous studies of experimental neuromas have indicated that some axons terminating in the neuroma exhibit both spontaneous and mechanosensitive discharges. Since these spontaneous discharges appear to occur in potentially nociceptive axons (A delta and C fibers), it has been speculated that this activity may relate to pain that occurs after peripheral nerve injury. Recent results from our laboratory have revealed several possible sources of error in prior electrophysiological studies of neuromas. Most notably, gallamine, a muscle-paralyzing agent that has been used in the majority of previous studies of experimental neuromas, has profound potassium-channel-blocking properties that may increase spontaneous activity in damaged axons. The present study was conducted to re-evaluate the incidence of spontaneous activity in experimental neuromas, and the fiber types involved in these discharges. A group of 44 male Sprague-Dawley rats underwent unilateral saphenous axotomy 1-8 weeks prior to acute neurophysiological recording experiments, and 6 additional rats underwent acute control recording procedures only. Recording was performed in all animals using a modification of the microfilament recording technique to determine the conduction velocities (CVs) and origins of spontaneously discharging axons. A thorough search for spontaneous discharges was made in each nerve both before and after the administration of gallamine. Spontaneous activity was rare in acutely severed saphenous nerve and was not significantly affected by gallamine administration. In rats with 1- to 4-week-old experimental saphenous neuromas, spontaneous activity was rare but was increased by a factor of 12.75 after gallamine treatment. Gallamine administration produced significantly more of both A alpha beta and A delta activity, compared to control recordings. No spontaneous C-fiber activity was found originating in neuromas either before or after gallamine. C-fiber spontaneous discharges in the apparently isolated saphenous nerve segment had receptive fields in fascia, superficial vasculature, and hairy skin of the medial hindlimb. Our conclusions are as follows: (1) Neuromas exhibit only rare spontaneous discharges unless exposed to potassium-channel-blocking agents; (2) all C-fiber activity recorded in saphenous nerve with a distal neuroma is derived from vascular, fascial, and other receptive fields rather than from the neuroma; (3) these data are consistent with known clinical phenomena in that neuromas are not usually spontaneously painful.