Search

During percutaneous microcompression of the gasserian ganglion for the relief of trigeminal neuralgia, a computerized technique for monitoring the pressure inside Meckel's cave was employed in 22 patients. A dedicated transducer connected to a computer records the balloon inflation pressure. Its variations are discernible within tenths of a bar and are plotted in relation to time. The intraoperative pressure inside Meckel's cave is from 0.9 to 2.4 bars. When pressure was low, there was recurrence of pain. The highest values of pressure (1.9-2.4 bars) were observed in most of the patients suffering from untoward side effects. The clinical results seem to be influenced by the level of the intraoperative intracavitary pressure.

Analysis of verbal responses to electrical stimulation of the trigeminal ganglion and rootlets has been the only method available so far to localize the electrode tip in the most appropriate trigeminal division or division segment, prior to thermocoagulation during percutaneous treatment for trigeminal neuralgia. A diversity of factors may lead to unreliable verbal responses, resulting in increased morbidity or even therapeutic failure. In an attempt to enhance the accuracy of electrode localization during Sweet's procedure, we describe an electrophysiological method complementary to clinical responses. Sensory trigeminal evoked potentials (STEPs) induced by separate successive orthodromic cutaneous stimulation of the three trigeminal divisions and recorded by the isolated tip of a transoval thermocouple electrode, together with motor trigeminal evoked potentials (MTEPs) elicited by stimulation of the trigeminal ganglion and recorded in the ipsilateral temporal muscle, were sequentially examined in six patients undergoing percutaneous tic treatment during gradual rostro-caudal electrode withdrawal. STEPs and MTEPs showed appropriate correlation with verbal and clinical motor responses at each electrode site. General anaesthesia failed to affect STEPs. Systematic exploration in the awake patient of both verbal and clinical motor responses, together with STEPs and MTEPs, is therefore recommended prior to the induction of radiofrequency lesions in the course of percutaneous treatment for trigeminal neuralgia.

A bipolar electrode has been designed to assess the possibility of locating accurately the electrode tip position within a nerve pathway prior to its thermal coagulation without having recourse to a wake-up procedure. By electrically stimulating each of the peripheral divisions of the trigeminal nerve and recording the evoked activity pre-ganglionically from the electrode, using an averaging computer, a clear triphasic response is recorded. The amplitude of this wave is largest when the electrode is within the stimulated division, thereby confirming electrically the anatomical location. By incorporating a thermocouple in the tip of the electrode a precisely controlled thermocoagulation can then be achieved using a radiofrequency generator. A preliminary series of 12 patients with trigeminal neuralgia requiring operative treatment were assessed in this study. In eight cases a clear response was obtained, in two the signal-to-noise ratio was too small, in one stimulus artefact obscured the response and in one a blood vessel was hit.

Trigeminal neuralgia may be treated in several ways. In the present study the efficacy of a selective percutaneous radiofrequency neurolysis in the gasserian ganglion was evaluated in 172 patients. A complete result was seen in 96.5% of the patients. The recurrence rate within 2 years amounted to 28.3%. Forty-seven patients underwent several treatments with a maximum of four within this period of time. The recurrence rate in the entire study population after 2 years was 8.1%. The mean follow-up period was 50 months (range 9-90 months). Except for the occurrence of corneal anaesthesia in 4% of the patients no serious complications were encountered.

Trigeminal neuralgia is an exactly defined syndrome with a non-uniform aetiology but an obviously uniform pathogenesis. A subdivision in an idiopathic and a symptomatic type is non-essential. In a part of the cases microvascular compression of the sensory root may be the cause of trigeminal neuralgia but there are some good arguments against this concept. Other causes such as multiple sclerosis, acoustic neuroma or carotid aneurysm are well known. The principle of neurosurgical procedures is either an interruption of the pain-conducting fibres or a non-specific manipulation at the Gasserian ganglion or the sensory root with the result of an interruption of abnormal ephapses and short-circuits which may recur later on. So microvascular decompression should not be considered to be a specific and causal therapeutic approach as well as the therapy of first choice for all cases.

Nineteen patients with trigeminal neuralgia were treated with either trigeminal ganglion glycerolysis or glycerolysis and intracranial microvascular decompression. All had a good degree of pain relief. Of those receiving glycerol alone (group A), 50% subjectively reported a mild reduction of fine tactile sensation. A similar response was reported by those treated with both glycerol and decompression (group B). The degree of sensory loss was so mild that thermal testing was useless as a discriminatory tool. The degree of sensory loss was not greater when both surgical procedures were performed than when the less-invasive trigeminal ganglion glycerolysis alone was used.

We report on diagnosis, treatment and clinical course of a solitary schwannoma of the trigeminal nerve with consecutive metastatic spread in a 45-year-old woman. The patient presented a temporal lobe syndrome with psychomotor seizures. Trigeminal nerve function was intact apart from a transient hypaesthesia in the mandibular branch. Assuming a meningioma the tumor was removed via a temporal approach. Secondary to the definitive histological diagnosis radiation therapy was performed. After that the patient was symptom-free. 4 months later a large recurrent tumor was found involving the cavernous sinus and the pterygopalatine fossa. In a second operation the tumor was resected intra- and extradurally through an infratemporal preauricular approach in cooperation with an oral and maxillo-facial surgeon. At this time multiple pulmonary metastases developed showing no response to polychemotherapy (EVI). The patient died 13 months after onset of the disease. Hitherto, only 5 cases of a primary malignant schwannoma of the trigeminal nerve have been published in the world literature.

Sudden blindness during percutaneous thermocoagulation of the gasserian ganglion occurred in a 72-year-old woman with trigeminal neuralgia. Considered a safe procedure, we highlight the possibility of this serious complication which was probably due to direct damage of the optic nerve.

The authors describe instruments which make it possible to perform retrogasserian thermolesions (RGT), glycerol radiculolysis (GRL) or trigeminal balloon compression (TBC) or possibly a combination of these methods from a single surgical approach. This makes it possible to adjust the selection of the type of lesion to unforeseen conditions any time during the operation. The surgical results are compared in 308 RGT, 50 GRL and 22 TBC. There are no substantial differences and therefore the selection of the type of lesion depends on technical circumstances during operation.

Long-term results (average follow-up, 9.3 years) obtained in 1000 consecutive patients suffering from cryptogenetic ("essential") trigeminal neuralgia treated with percutaneous thermorhizotomy are analyzed. Pain relief was obtained in 95% of the treated patients. Permanent morbidity was as follows: masseter weakness in 105 patients; oculomotor palsies in 5 patients; weakening of the corneal reflex in 197 patients, 6 of whom requested an ocular operation for keratitis; and painful dysesthesia in 52 patients, 15 of whom developed a painful anesthesia syndrome. There was a recurrence rate of 18.1%, and a correlation between postoperative sensory deficit and the cure rate was found. These results are discussed and compared to the results obtained with different techniques.

The treatment of trigeminal neuralgia (TN), which is resistant to medical therapy, has benefited from many surgical techniques. It is not possible, in light of the present level of knowledge, to establish exactly which method is the most suitable. It does, however, seem significant that certain side effects appear, in varying percentages, in all kinds of operations. In 13 years, 2,094 patients suffering from TN have been treated by the authors with percutaneous Gasserian neurolysis, 128 patients with radiofrequency trigeminal neurolysis, and 1,966 with selective ethanolic trigeminal neurolysis (SETN). Our experience treating TN with controlled increments of ethanol by means of a needle introduced through the oval foramen in the Gasserian ganglion is related here. The tip of the needle is accurately placed among the roots desired under fluoroscopic control. The clinical effects on the conscious patient of a prognostic block with local anesthetics are evaluated before producing the neurolysis. Follow-up has been long enough to show that SETN is a highly selective procedure, which shouldn't be underrated in the centers that use it routinely.

The trigeminal neuralgia has to be differentiated from the trigeminal neuropathy in respect of pain character and etiology. The neuralgia is characterized by paroxysmal pain evoked by trigger stimuli. The most frequent cause of this type of pain is a parapontine vascular compression of the trigeminal root without neurological deficits. The symptoms of neuropathy are some sensory loss associated with continuous pain resulting from peripheral damage of the trigeminal nerve. This distinction alleviates the indication for specific operative procedures and is more precise than the subdivision in typical and atypical neuralgia. The results of neurovascular decompression and thermorhizotomy can be much improved if neuropathic pain syndromes are excluded from operation. Out of 180 patients suffering from trigeminal neuralgia 94% were pain-free after neurovascular decompression and 96% of 144 patients following thermorhizotomy. For the treatment of continuous neuropathic pain augmentative electrostimulation of the Gasserian Ganglion via implanted electrodes is recommended.

This study includes 127 patients treated for typical trigeminal neuralgia, 74 of whom underwent a percutaneous microcompression (PMC), 33 a radiofrequency thermocoagulation (RFT) and 20 were explored for microvascular decompression (MVD). A mean follow-up of 24 months was reached by all the groups. Pain relief was evaluated as an 'all or none' effect. At hospital discharge, pain had disappeared in 93.2% of the patients treated with PMC, in 81.8% of those treated with RFT, and in 85% of the MVD group. At 24 months the effect was maintained by 57.2% of the PMC group, 57.6% of the RFT, and by 75% of the MVD group. Marked dysesthesia was reported by 6.7% of the patients treated with PMC, and by 24.2% of those who received a RFT. Impairment of masticatory function was observed in 10% of the PMC patients. Ipsilateral hypoacusia and transient IV nerve palsy in 1 patient was the only major complication after MVD.

A 39-year-old woman had a large benign intracranial schwannoma of the Gasserian ganglion. Thirty-two years previously, she had an embryonal rhabdomyosarcoma of the orbit. She had been treated by enucleation, local excision, and low-dose supplemental irradiation (1,400 rads). This is the longest survival of which we are aware following any treatment modality in such tumors. No correlation between the two tumors has been established.

The results of EEG investigations after Spiller-Frazier's operation for trigeminal neuralgia in 112 patients are reported. Follow-up EEGs were recorded within 1-8 years after surgery; two to three follow-up tracings were available in 53 patients. Two distinct phases of EEG alterations were noted: 1) The immediate postoperative phase characterized by bilateral delta waves of maximal distribution in the frontal-precentral area and in the temporal area on the side of surgery. Such alterations are supposedly due to postoperative edema or associated metabolic disturbances. 2) Several months after surgery focal abnormalities of the temporal lobe develop, which consist of high amplitude alpha-, beta- or theta-waves, sharp waves, spikes and occasional stypical spike-and-wave complexes. These abnormalities are reflected on the contralateral side in approximately one third of the case. Repeated EEGs confirmed the consistency of degree and location of these findings with the exception of a less constant incidence of spikes and sharp waves. Severity of EEG abnormalities and incidence of potentially epileptogenic discharges increases with age. In spite of the precarious location of such focal abnormalities in the temporal lobe only 3 of 112 patients (2.7%) reported seizures with temporal lobe features. The age of the three patients was below the average age of 59.1 years. Seizures occurred sporadically beginning approximately 2 years after surgery. The low incidence of seizures may in our opinion be due to the advanced age of most patients.

owing to an enormous development in the operative technical possibilities, percutaneous surgical methods are available today for both destructive and functional pain interventions, so that the surgical risk can be reduced to a minimum and also patients in a poor general condition and of advanced age can tolerate these interventions at any time.

In the younger patient with trigeminal neuralgia refractory to medical treatment, microsurgical operation is warranted. If a truly significant compressive artery is found in relation to the posterior root, microvascular decompression is carried out. If no convincing evidence of a compressive vascular lesion is found at operation, the posterior root is partially sectioned. Most patients with tic douloureux are elderly and in these, and in all patients who prefer a minor procedure, I favor the simple low morbidity percutaneous radiofrequency technique. In these days of informed consent, patients should preoperatively be made aware of the advantages of both kinds of operations and participate in choosing the procedure which best suits the individual's health and preferences.

The authors report on indications and results of percutaneous surgical treatment of trigeminal neuralgia based on own experiences in 1124 cases. In 912 cases percutaneous thermorhizotomy and in 212 cases percutaneous microcompression have been used. As a conclusion the following considerations have been stressed: I) In both methods slight hypaesthesia appears to obtain good pain relief; II) Percutaneous thermorhizotomy is indicated in third division neuralgias; III) Percutaneous microcompression is indicated for first and second division neuralgias only when the trigeminal cistern is not abnormally dilated; IV) Undesirable side-effects after either thermorhizotomy and microcompression are similar and transitory in most cases; V) Pain recurrence for both procedures are comparable and range at about 25%.

A patient is described with aspergillus flavus granuloma of the trigeminal ganglion. The patient was effectively treated by surgical excision of most of the infected tissue followed by intensive chemotherapy with amphotericin B and flucytosine.

Lesions of the peripheral part of the trigeminal nerve may cause trigeminal neuropathy associated with severe pain. Such pain usually does not respond to carbamazepine and analgesics, and it is continuous and lacks the characteristic paroxysmal character of tic douloureux. These patients often present with complex changes of facial sensibility in the form of dysesthesia, hyperalgesia, and allodynia. The pain sometimes responds favorably to transcutaneous nerve stimulation, but direct stimulation of the trigeminal ganglion and rootlets via an implanted electrode provides a greater likelihood of pain relief. Fourteen patients diagnosed as having painful trigeminal neuropathy received implants of a gasserian ganglion-stimulating electrode. The mean follow-up period is 4 years (range, 1 to 7 years). Eleven of the patients have retained the pain-relieving effect, and 1 had pain disappear without further stimulation. Eight of the patients estimated their pain relief to be complete or very good. There were no serious complications, but in several of the patients the electrode had to be exchanged because the insulation of the lead wires broke. For the selection of patients for permanent electrode implantation, a method has been developed for trial stimulation via a percutaneous electrode introduced into the trigeminal cistern. Temporary trial stimulation can be performed for several days. It is concluded that stimulation of the trigeminal ganglion and rootlets with the aid of an implanted electrode may effectively relieve certain forms of trigeminal pain that are otherwise extremely difficult to manage.

Nerve fibers in the dental pulp of the lower molar teeth of the rat exert fluoride resistant acid phosphatase (FRAP) activity. FRAP-positive axons establish a three-dimensional nerve plexus within the pulp; the individual axons are very fine (calibre less than 1 micrometer) and only their varicosities measure 1...2 micrometer in diameter. Electron microscopically, FRAP-positive amyelinate axons containing lysosomes are partly embedded in Schwann cells. Removal of the cervical superior ganglion does not induce any alteration of FRAP-positive axons, while destruction of the Gasserian ganglion results in Wallerian degeneration. No FRAP-positive nerve fibers were found in rat incisors. Since, in the rat, only molar teeth are equipped with nociceptive terminals while continuously growing incisors lack pain fibers, it is concluded that FRAP-positive varicose axons in the dental pulp represent nerve endings of trigeminal primary nociceptive neurons.

Between 1974 and 1984, 428 trigeminal neuralgia cases were treated by controlled radiofrequency thermocoagulation (RFTC). 29 had recurrent trigeminal neuralgia after intracranial surgery. 26 of the 29 patients were treated by retrogasserian rhizotomy and 3 by posterior fossa exploration. Among the 26 recurrent trigeminal neuralgia following retrogasserian rhizotomy, RFTC was effective in 23 cases (88.5%), and in 3 cases (11.5%) RFTC was effective for a short period. Repeated RFTC was unable to control the pain attacks which were later relieved by posterior fossa exploration and root section. Of the 3 recurrent trigeminal neuralgia following posterior fossa exploration, RFTC was effective in 2 cases (66.6%).

These first ultrastructural studies of the effect caused by thermocoagulation of a ganglion (ganglion inferius nervi vagi) akin to the Gasserian ganglion have shown that selective pain fiber elimination can only be expected from thermocoagulation at temperatures not higher than 50 degrees C/60 s or 60 degrees C/60 s. Even if the results of these animal experiments can only be applicable to clinical practice in the sense of an analogical conclusion, we are nevertheless of the opinion that it can be recommended to begin the thermocoagulation in trigeminus neuralgia at low temperatures (50 degrees C/60 s or 60 degrees C/60 s) and only if found necessary, after checking the sensitivity to pain, to increase it in steps of 5--10 degrees C.

This study determined the cardiovascular effects of percutaneous radiofrequency coagulation of the Gasserian ganglion, performed under neuroleptanalgesia and intermittent ultrashort-acting barbiturate anaesthesia. Twelve ASA physical status class II patients were studied. Highly significant increases in mean heart rate and arterial blood pressure followed the insertion of the cannula electrode into the Gasserian ganglion (p less than 0.001). In six randomly assigned patients severe tachycardia and hypertension also accompanied the progress of the thermal lesion (p less than 0.0001). Three patients developed premature ventricular contractions, and two developed significant ST segment depression. Intravenous nitroglycerin, used during current generation, successfully controlled the hypertensive response in the other six patients. In percutaneous thermocoagulation of the Gasserian ganglion the patient's co-operation is essential. In addition to providing suitable operating conditions for both surgeons and patient, we should also be able to maintain normal and stable cardiovascular haemodynamics. Intravenous nitroglycerin used as an adjunct to light general anaesthesia safely maintained intraoperative normotension. It is also suggested that patients with coronary artery disease be adequately monitored and protected during the procedure.

A case of carotid-cavernous fistula following percutaneous trigeminal ganglion approach is presented. The case was treated by a combination of trapping and embolisation of the carotid artery. Percutaneous approach to the trigeminal ganglion via the foramen ovale was described by Taptas (1911) and Hartel (1914). Since then this procedure has been used in large series, for the injection of alcohol (Harris, 1940), electrocoagulation (Kirschner, 1942) or the injection hot water (Jeager, 1957) to the trigeminal ganglion for the treatment of trigeminal neuralgia. In 1965 White and Sweet used the percutaneous trigeminal ganglion approach for the radio-frequency (R.F.) thermocoagulation of the trigeminal ganglion. This procedure is a simple and safe method. It has been used in large series in the treatment of trigeminal neuralgia. In our department we have performed 252 R.F. thermocoagulation of the gasserion ganglion in 228 patients since 1975. In 252 interventions using the percutaneous trigeminal ganglion approach, via the foramen ovale, we observed only one carotid-cavernous fistula following the procedure. This is the second report in the literature of a carotid-cavernous fistula following the percutaneous trigeminal ganglion approach.

Immunoreactive substance P is present in measurable amounts in pia arachnoid from rat, cat, dog and calf. Levels of substance P in this tissue are comparable to those found in peripheral structures receiving innervation from dorsal root or trigeminal ganglia. Separation and measurement of bovine pia-arachnoid extract by reverse phase high performance liquid chromatography and radioimmunoassay reveals a single peak of activity with a retention time identical to that of substance P. Unilateral lesions of the trigeminal ganglia decrease substance P levels within cat pia arachnoid and accompanying blood vessels ipsilaterally by greater than 50%. These data indicate that most of the substance P surrounding pial blood vessels resides within afferent nerve fibres from trigeminal ganglion cells.

The authors report their experience of the treatment of essential trigeminal neuralgia by percutaneous thermocoagulation of the Gasserian ganglion (400 patients). This method has always been performed on anesthetized patients, using an ultra short acting barbiturate: methohexital. Most often, two or three successive coagulations are needed to obtain the desired analgesia. No complications have resulted, although 30 p. cent of our patients were over 70 years old.

Facilitation of the opiate-mediated system provides relief of excess pain but not of deafferentation pain. Influence on neuronal hyper-activity, which was provoked after the deafferentation of the peripheral trigeminal nerve (deafferentation hyperactivity; DH), by stimulation of the internal capsule (IC), VPM nucleus of the thalamus and by the cerebral sensorimotor cortex, was examined. This experiment demonstrates that a suppressive effect is exerted on the sustained neuronal hyperactivity, which was proved to have a close relationship with deafferentation pain. In the preliminary experiment, it was confirmed that DH was provoked by coagulation of unilateral (left side) Gasserian ganglion in 29 adult cats, who were allowed to survive up to 72 days. DH, sustained high amplitude discharge without any stimuli on the face or neck, was detected in the subnucleus caudalis of the spinal trigeminal nucleus (STNcd) of the denervated side. DH was never suppressed by facilitation of the opiate-mediated system. 87 of 113 neurones identified in the STNcd of the denervated side showed DH in another 18 cats. In 30 of 55 neurones examined, DH was conspicuously suppressed by the stimulation of contralateral (right) side, 11 of 29 neurones by ipsilateral IC. Five of 13 neurones were suppressed by contralateral VPM stimulation, 2 of 3 neurones by ipsilateral stimulation. Stimulation of cortical area, SM1 of MS1, in other 15 cats, considerably suppressed DH in STNcd. Microinjection of wheat-germ-agglutinin in the cerebral cortex revealed in direct projection of the descending fibre from MS1 to STNcd and brain stem reticular formation via IC.(ABSTRACT TRUNCATED AT 250 WORDS)

483 patients were operated on one of the percutaneous method. The radiofrequency thermocoagulation, the application of glycerol to the trigeminal cistern and the balloon compression of the ganglion were used. There are no substantial differences in the results and number of recurrences obtained with any of the different lesions. The choice of the type of lesion is often appointed by technical circumstances. The kind of instrumentarium which permits to perform in a single approach one of the three types of trigeminal lesion or there combination was designed.

A retrospective review of 12 cases of meningioma of Meckel's cave involving the Gasserian ganglion or the trigeminal posterior root (or both) seen at the Mayo Clinic during a 20-year period suggested three clearly defined clinical groups. One group (the largest) had typical trigeminal neuralgia and an excellent prognosis after the removal of the easily detachable mass that was impinging on the ganglion. A second group, with meningiomas en plaque embedded in the ganglion, had a history of atypical trigeminal face pain without neurological deficit, but the prognosis for pain relief was not as good as in the previous group. A third group had a history of face dysesthesias and pain, objective trigeminal sensory loss, and multiple cranial nerve deficit; these patients had meningiomas with histological signs of mitotic activity and a poor prognosis, with return of intractable pain and recurrence of the tumor.

We report about hypertensive crises, cardial arrhythmia and respiratory complications in 47 patients undergoing thermocoagulation of the gasserian ganglion. Therapeutic proposals are discussed.

Among the complications after surgical interventions carried out on the Ganglion semilunare because of a trigeminal neuralgia the reason why Keratopathia neuroparalytica plays a role is the fact that it very frequently leads to partial or total blindness of the affected eye. The pathogenesis of the keratopathy is still being disputed. The appraisal of the various surgical methods in trigeminal neuralgia always includes the frequent occurrence of a keratopathy. Among the 171 patients who were operated on in Halle because of trigeminal neuralgia in the last ten years no keratopathy was observed. In 12 cases a reduction or removal of the corneal reflex was brought about. On 8 patients a postganglionic intradural operation was carried out, all others received an electro-coagulation. The co-operation with the ophthalmologist is indispensable both prophylactically and therapeutically.

Thirty-eight patients with facial pain in the trigeminal distribution have been treated by percutaneous coagulation of the trigeminal ganglion. Although use has been made of radiological criteria, it has been found from the physiological data obtained from stimulation that motor and sensory phenomena provide more information of electrode placement and that good pain relief results when these criteria are met. The advantages of the method are: (i) minimal operative risk; (ii) control of the extent of the lesion created; (iii) small sensibility deficit; (iv) minimal complication rate; (v) short hospitalization; (vi) satisfactory result in more than 90% of patients; (vii) no recurrence of pain to date.

Percutaneous thermocoagulation of the Gasserian ganglion allows a good preservation of facial touch sensation with a complete and immediate regression of the symptomatology in a majority of cases. Neurophysiological bases are the peculiar resistance to the thermal lesion of the large myelinated fibers compared to the relatively smaller fibers. The study of the cortical-evoked responses before and after surgery suggests that the afferent volley travels in preference along these large myelinated fibers.

The development of a facial flush during thermocoagulation of the Gasserian ganglion was monitored in 16 patients with pulse recording techniques and in a further 17 patients with thermography. There was a close association between the development of the facial flush in the distribution of one or more divisions of the trigeminal nerve and the subsequent demonstration of postoperative analgesia. In regions where significant changes took place, vascular pulsations increased 25-233% (mean 96%) and facial temperature rose 0.5-2.0 degrees C. The response persisted for up to an hour postoperatively, and was not diminished in patients with pre-operative analgesia from a previous procedure. Possible mechanisms for the facial flush, including stimulation of an active vasodilator system, the antidromic release of vasoactive substances from trigeminal nerve terminals and the release of tonic vasoconstriction are discussed. A practical application of the pulse recording technique used in the present investigation would be to monitor the distribution of vasodilatation at operation to avoid unwanted first division sensory loss.

Voltage and current within Gasserian ganglion have been measured during a therapeutical high frequency coagulation of the Gasserian ganglion in 25 consecutive cases. From these values, the impedance (Ohm), the work (Watt) and the total energy (Joule) necessary to obtain an analgesia without anesthesia have been calculated. The study has shown that the temperature and the time of coagulation in correlation with the length of the non isolated tip of the electrode are actually the only constancy in the control of the therapeutical lesions.