Factors predictive of suboptimal seizure control following selective amygdalohippocampectomy

2002 ◽  
Vol 97 (5) ◽  
pp. 1142-1151 ◽  
Author(s):  
Aviva Abosch ◽  
Neda Bernasconi ◽  
Warren Boling ◽  
Marilyn Jones-Gotman ◽  
Nicole Poulin ◽  
...  
Keyword(s):  
Mr Imaging ◽  
Seizure Control ◽  
Mesial Temporal Lobe Epilepsy ◽  
Class Iii ◽  
Strict Adherence ◽  
Content Type ◽  
Selective Amygdalohippocampectomy ◽  
Postoperative Seizure ◽  
Histopathological Studies ◽  
Fine Print

Object. Selective amygdalohippocampectomy (SelAH) is used in the treatment of mesial temporal lobe epilepsy (MTLE). The goal of this study was to determine factors predictive of poor postoperative seizure control (Engel Class III or IV) following SelAH. Methods. A retrospective study was conducted of 27 patients with poor seizure control postoperatively (Engel III/IV group), in comparison with 27 patients who were free from seizures after surgery (Engel I/II group). The results of electroencephalography, magnetic resonance (MR) imaging, and pathological studies were reviewed, and volumetric MR image analysis was used to compare the extent of the mesial structures that had been resected. In 56% of patients in the Engel III/IV group, significant bitemporal abnormalities were displayed on preoperative EEG studies, compared with 24% of patients in the Engel I/II group (p < 0.05). An analysis of preoperative MR images disclosed five patients (19%) in the Engel III/IV group and no patient in the Engel I/II group with normal hippocampal volumes bilaterally. Thirteen patients in the Engel III/IV group subsequently underwent either extension of the SelAH (six cases) or a corticoamygdalohippocampectomy (seven patients). Three patients from the former and one patient from the latter subgroup subsequently became seizure free (four patients total [34%]). The remaining nine patients did not improve, despite the fact that they had undergone near-total resection of mesial structures. Conclusions. The majority of patients receiving suboptimal seizure control following SelAH did not meet the criteria for unilateral MTLE, based on EEG, MR imaging, and/or histopathological studies. These patients were therefore unlikely to benefit from additional resection of mesial structures. With the benefits of modern imaging, and by strict adherence to selection criteria, SelAH can be predicted to yield excellent postoperative seizure control for nearly all patients with unilateral MTLE. There remains a subpopulation, however, that meets the criteria for MTLE, but does not become free from seizure following SelAH.

Long-term seizure outcomes following amygdalohippocampectomy

2003 ◽  
Vol 98 (4) ◽  
pp. 751-763 ◽  
Author(s):  
H. Gregor Wieser ◽  
Marcos Ortega ◽  
Alon Friedman ◽  
Yasuhiro Yonekawa
Keyword(s):  
Mesial Temporal Lobe Epilepsy ◽  
Outcome Data ◽  
University Hospital ◽  
Seizure Outcome ◽  
Content Type ◽  
Selective Amygdalohippocampectomy ◽  
Class 1 ◽  
Fine Print

Object. Analyses of the results of surgery for epilepsy are hindered by inconsistent classifications of seizure outcome, small numbers of patients, and short postoperative follow-up periods. The authors conducted a retrospective study with a reassessment of the long-term seizure outcomes in patients who underwent selective amygdalohippocampectomy (SelAH) for pharmacotherapy—resistant mesial temporal lobe epilepsy (MTLE) at the Zurich University Hospital from 1975 to 1999. Methods. Year-by-year data and the last available data on seizure outcomes were retrospectively assessed for 369 consecutively surgically treated patients who had participated in a follow-up period longer than 1 year as of 1999 and whose outcomes were classified according to the Engel scale and the proposed new International League Against Epilepsy (ILAE) scale. Patients were grouped into nonlesional and lesional MTLE groups depending on whether they harbored a gross anatomical lesion that caused the MTLE. Differentiation was made between curative and palliative operations. Complications related to surgery are reported for 453 patients who underwent SelAH and participated in more than 3 months of follow-up review. The last available outcome data according to the Engel scale were found to be generally similar to those of the new ILAE classification, with 66.9% of patients free from disabling seizures (Engel Class I) compared with 57.1% who were completely seizure and aura free (ILAE Class 1). The last available data on seizure outcome were not significantly different between patients in the lesional and nonlesional MTLE groups. In the lesional group, seizure outcomes were significantly better when patients underwent surgery early in the course of the disease. Overall, 70% of the patients received reductions in their antiepileptic drug treatment at the time of the last available follow-up review. Complications related to the surgical procedures were rare. Conclusions. The authors conclude that SelAH is a safe and effective surgical procedure for MTLE.

Gamma knife radiosurgery for hypothalamic hamartomas in patients with medically intractable epilepsy and precocious puberty

2000 ◽  
Vol 92 (4) ◽  
pp. 726-731 ◽  
Author(s):  
Frank Unger ◽  
Oskar Schröttner ◽  
Klaus Haselsberger ◽  
Eva Körner ◽  
Robert Ploier ◽  
...  
Keyword(s):  
Mr Imaging ◽  
Gamma Knife ◽  
Precocious Puberty ◽  
Seizure Control ◽  
Gamma Knife Radiosurgery ◽  
Content Type ◽  
Hypothalamic Hamartomas ◽  
Gelastic Epilepsy ◽  
Fine Print

✓ Hamartoma of the hypothalamus represents a well-known but rare cause of central precocious puberty and gelastic epilepsy. Due to the delicate site in which the tumor is located, surgery is often unsuccessful and associated with considerable risks. In the two cases presented, gamma knife radiosurgery was applied as a safe and noninvasive alternative to obtain seizure control.Two patients, a 13-year-old boy and a 6-year-old girl, presented with medically intractable gelastic epilepsy and increasing episodes of secondary generalized seizures. Abnormal behavior and precocious puberty were also evident. Magnetic resonance (MR) imaging revealed hypothalamic hamartomas measuring 13 and 11 mm, respectively. After general anesthesia had been induced in the patients, radiosurgical treatment was performed with margin doses of 12 Gy to 90% and 60% of isodose areas, covering volumes of 700 and 500 mm3, respectively.After follow-up periods of 54 months in the boy and 36 months in the girl, progressive decrease in both seizure frequency and intensity was noted (Engel outcome scores IIa and IIIa, respectively). Both patients are currently able to attend public school. Follow-up MR imaging has not revealed significant changes in the sizes of the lesions.Gamma knife radiosurgery can be an effective and safe treatment modality for achieving good seizure control in patients with hypothalamic hamartomas.

Incidence of seizures after surgery for supratentorial meningiomas: a modern analysis

1996 ◽  
Vol 84 (3) ◽  
pp. 382-386 ◽  
Author(s):  
Bruce S. Chozick ◽  
Steven E. Reinert ◽  
Samuel H. Greenblatt
Keyword(s):  
Mr Imaging ◽  
Seizure Control ◽  
Outcome Variable ◽  
Diagnostic Model ◽  
Seizure Outcome ◽  
Chi Square ◽  
Content Type ◽  
Modern Analysis ◽  
Postoperative Hydrocephalus ◽  
Postoperative Seizure

✓ The authors have assessed the incidence of postoperative seizures in 158 patients with supratentorial meningiomas diagnosed by computerized tomography (CT) and/or magnetic resonance (MR) imaging, which theoretically should lead to early diagnosis and treatment and the potential for improved seizure outcome. Univariate chi-square and logistic regression analyses were performed on 24 independent variables against the outcome variable of occurrence of a postoperative seizure. The median duration of preoperative seizures was 1 month, considerably shorter than that found in studies conducted prior to the advent of CT and MR imaging. Of 63 patients with a history of preoperative seizures, 40 (63.5%) had complete cessation of seizures after surgery. Twelve (92.3%) of 13 patients with one to three postoperative seizures eventually achieved complete seizure control, whereas only four (40%) of 10 patients with more than three postoperative seizures achieved this result. Overall, 88.9% of patients with preoperative seizures achieved complete seizure control postoperatively. Multivariate analysis was used to identify six variables that were predictive of the occurrence of postoperative seizures: preoperative seizure history, preoperative language disturbance, extent of tumor removal, parietal location of tumor, postoperative anticonvulsant medication status, and postoperative hydrocephalus. These variables were incorporated into a diagnostic model designed to predict the risk of a postoperative seizure following meningioma surgery. On the basis of their findings, the authors conclude that earlier detection and treatment of supratentorial meningiomas improve seizure outcome in patients with preoperative epilepsy. Furthermore, an assessment of the risk of postoperative seizures may help guide decisions concerning weaning patients from anticonvulsant medications postoperatively.

Intraoperative hippocampal electrocorticography to predict the extent of hippocampal resection in temporal lobe epilepsy surgery

2000 ◽  
Vol 93 (1) ◽  
pp. 44-52 ◽  
Author(s):  
Guy M. McKhann ◽  
Julie Schoenfeld-McNeill ◽  
Donald E. Born ◽  
Michael M. Haglund ◽  
George A. Ojemann
Keyword(s):  
Temporal Lobe Epilepsy ◽  
Temporal Lobe ◽  
Seizure Control ◽  
Epileptiform Activity ◽  
Neuronal Loss ◽  
Mesial Temporal Lobe Epilepsy ◽  
Mesial Temporal Sclerosis ◽  
Content Type ◽  
Pathological Subtype ◽  
Fine Print

Object. Among the variety of surgical procedures that are performed for the treatment of medically refractory mesial temporal lobe epilepsy (TLE), no consensus exists as to how much of the hippocampus should be removed. Whether all patients require a maximal hippocampal resection has not yet been determined.Methods. At the University of Washington, all TLE operations are performed in a tailored fashion, guided by electrocorticography (ECoG). The amount of hippocampal resection is determined intraoperatively by the extent of interictal epileptiform abnormalities on ECoG recorded from that structure, resulting in a hippocampal resection that is individualized for each patient. Using this approach, the authors prospectively observed 140 consecutive patients who underwent surgery for mesial TLE with pathological diagnoses of either mesial temporal sclerosis with neuronal loss (MTS group) or mild gliosis without neuronal loss (non-MTS group) to determine whether the extent of hippocampal resection correlates with outcome when a tailored approach is used. Additionally, the authors analyzed whether the presence of residual interictal epileptiform activity on ECoG following mesial temporal resection predicts poorer seizure control.With at least 18 months of clinical follow up, 67% of the 140 patients were seizure free or had only a single postoperative seizure. There was no correlation between the size of the hippocampal resection and seizure control in the group as a whole or when stratified by pathological subtype. Using an intraoperatively tailored strategy, individuals with a larger hippocampal resection (> 2.5 cm) were not more likely to have seizure-free outcomes than patients with smaller resections (p = 0.9). Additionally, both MTS and non-MTS patients, in whom postoperative ECoG detected residual epileptiform hippocampal (but not cortical or parahippocampal) interictal activity following surgical resection, had significantly worse seizure outcomes (p = 0.01 in the MTS group; p = 0.002 in the non-MTS group).Conclusions. Intraoperative hippocampal ECoG can predict how much hippocampus should be removed to maximize seizure-free outcome, allowing for sparing of possibly functionally important hippocampus.

Transparahippocampal selective amygdalohippocampectomy in children and adolescents: efficacy of the procedure and cognitive morbidity in patients

2000 ◽  
Vol 93 (3) ◽  
pp. 402-409 ◽  
Author(s):  
Shenandoah Robinson ◽  
T. S. Park ◽  
Lynn B. Blackburn ◽  
Blaise F. D. Bourgeois ◽  
Susan T. Arnold ◽  
...  
Keyword(s):  
Children And Adolescents ◽  
Temporal Lobe ◽  
Seizure Control ◽  
Content Type ◽  
Clinical Variables ◽  
Selective Amygdalohippocampectomy ◽  
Significant Difference ◽  
Temporal Lobe Seizures ◽  
Mesial Temporal Lobe ◽  
Fine Print

Object. Unilateral resection of the hippocampus and amygdala can be used to treat medically intractable mesial temporal lobe seizures. To date seizure outcome and the extent of cognitive morbidity have been unknown in children following the transparahippocampal variation of selective amygdalohippocampectomy (TSA), which prompted the present prospective study.Methods. Preoperative examinations and outcomes in 22 consecutive children and adolescents who underwent TSA were studied. Cognitive and psychological morbidity were assessed using standard neuropsychological instruments. The authors evaluated relationships between seizure control and cognitive morbidity and 13 and nine clinical variables, respectively.Seizure control was achieved in 11 (65%) of 17 patients (> 2 years follow up). Among 13 clinical variables, the only preoperative finding that had a significant bearing on seizure control was the presence of unilateral hypometabolism, which could be observed on [18F]fluorodeoxyglucose—positron emission tomography scans (p < 0.001). Patients with seizure control showed significant improvements in verbal and full scale intelligence quotients (both p = 0.05). Patients with longer preoperative durations of seizures exhibited more cognitive impairment that persisted postoperatively. Cognitive outcome analysis based on nine clinical factors revealed no significant difference in cognitive parameters postoperatively, except that significant improvement occurred in rote verbal memory scores among patients who underwent right-sided TSA (p = 0.01). Individually, 81% of the children achieved significant improvement in at least one of seven cognitive parameters, and 52% had stable or improved scores in all parameters.Conclusions. The results indicate that TSA is a safe effective approach for the treatment of medically intractable mesial temporal lobe seizures in children with minimum effect on cognitive morbidity. Given that the literature suggests that children suffer progressive cognitive morbidity from persistent seizures, the results of this study support early surgical intervention for this group of children.

Surgical management of epilepsy associated with cerebral arteriovenous malformations

1990 ◽  
Vol 72 (2) ◽  
pp. 216-223 ◽  
Author(s):  
Hwa-Shain Yeh ◽  
Shiro Kashiwagi ◽  
John M. Tew ◽  
Thomas S. Berger
Keyword(s):  
Temporal Lobe ◽  
Seizure Control ◽  
Focal Cerebral Ischemia ◽  
Epileptic Activity ◽  
Content Type ◽  
Depth Electrodes ◽  
Medication Side ◽  
Postoperative Seizure ◽  
Fine Print ◽  
Seizure Foci

✓ Between 1982 and 1986, 27 patients with seizure disorders due to cerebral arteriovenous malformation (AVM) were surgically treated by the authors. These patients had no history or clinical manifestation of intracranial hemorrhage. All were treated with anticonvulsant agents by their neurologists but became disabled due to inadequate control of seizures by medication, side effects of the anticonvulsant drugs, or the effects on their professional lives of even infrequent seizures. The age of the patients ranged from 13 to 61 years. There were 13 males and 14 females. The AVM's were smaller than 2 cm in four patients, between 2 and 4 cm in five, and larger than 4 cm in 18. The most frequent location of the AVM's was in the temporal lobe, followed by the frontal, parietal, and occipital lobes. All patients had preoperative electroencephalography (EEG) and intraoperative electrocorticography. Intraoperative recording of the amygdala and the hippocampus by depth electrodes was performed if the AVM's were located in the temporal lobe. Superficial or posterior temporal lobe AVM's often have remote seizure foci that involve the amygdala and hippocampus. All patients underwent craniotomy and total excision of their AVM's. Surgery was carried out under local anesthesia to allow localization by electrical stimulation if the AVM involved the speech area or the sensorimotor cortex. Based on the EEG findings, excision of the epileptogenic lesion in addition to the AVM was performed in 18 patients. In seven patients with AVM's located in the temporal lobe, remote seizure foci were identified and excised. The remote epileptic activity was particularly prominent in AVM's in the temporal lobe and usually involved mesial temporal structures. Microscopic study of excised seizure foci showed gliosis in 26 cases, hemosiderin deposits in 10, and focal hemorrhage in four. There were no operative deaths. Two patients developed a hemiparesis and three suffered temporary dysphasia after surgery. Two patients had visual field deficits. The results of postoperative seizure control during the average follow-up period of 3 years 11 months were excellent in 21 patients, good in three, fair in two, and poor in one. The latter patient, whose epileptic lesion was not completely excised because of its location in the motor cortex, had poor seizure control postoperatively. Another patient required a second operation to remove a remote seizure focus. In this series, proposed mechanisms of seizure associated with cerebral AVM include focal cerebral ischemia secondary to arteriovenous shunting, gliosis of the surrounding brain, and a secondary epileptogenesis in the temporal lobe. Successful seizure control can be obtained with wide excision of the epileptogenic foci surrounding the AVM's. In some circumstances, seizure foci remote from the vascular malformation must be excised.

Multiple subpial transections: outcome and complications in 20 patients who did not undergo resection

2002 ◽  
Vol 97 (1) ◽  
pp. 39-47 ◽  
Author(s):  
Johannes Schramm ◽  
Ales F. Aliashkevich ◽  
Thomas Grunwald
Keyword(s):  
Mr Imaging ◽  
Class Ii ◽  
Class I ◽  
Class Iii ◽  
Content Type ◽  
Surgical Methods ◽  
Over Time ◽  
Class Iv ◽  
Fine Print

Object. The authors describe patient characteristics, surgical methods, complications, and outcome over time in a cohort of patients who underwent multiple subpial transection (MST) without concomitant cortical resection. Methods. Twenty consecutive patients in whom drug-resistant epilepsy had been diagnosed a mean of 16 ± 9 years earlier (mean ± standard deviation [SD]) were treated with MST without cortical resection. The mean follow-up period was 49.3 ± 18.3 months (mean ± SD, median 58 months). At 12 months of follow up, two of the 20 patients were Engel Class I, one was Class II, six were Class III, and 11 were Class IV. At latest follow up, one patient was Engel Class I, one was Class II, seven were Class III, and 11 were Class IV. According to an alternative five-tiered classification system, two outcomes were excellent, seven were good, one was fair, nine were poor, and one was worse. Outcome was found to be better in patients with no lesions observed on magnetic resonance (MR) imaging, and worse in those with large MST areas. Outcome had a tendency to change (this occurred in 13 of 20 cases). Five patients (25%) improved and seven (35%) deteriorated in Engel outcome class, and in one (5%) both developments occurred over time. Most outcome class changes occurred before the end of the 2nd year (nine), and four were observed in the 5th year. There where seven transient neurological deficits and four surgical complications. There was no permanent significant morbidity, and there were no deaths. Conclusions. Forty-five percent of patients achieved a worthwhile improvement after pure MST, if Engel outcome Class III is deemed a worthwhile improvement. The alternative five-tiered classification resulted in 50% with worthwhile improvement (excellent, good, or fair outcome), 45% with poor, and 5% with worse outcome. Lesions that are detectable on MR imaging, and large MST areas are predictive of worse results. Significant intraoperative problems may arise, but this happens infrequently. There is a notable rate of transient morbidity but the rate of permanent morbidity is not significant.

Temporal characteristics of radiosurgical lesions in an animal model

1994 ◽  
Vol 80 (6) ◽  
pp. 1046-1055 ◽  
Author(s):  
David R. Blatt ◽  
William A. Friedman ◽  
Frank J. Bova ◽  
Daniel P. Theele ◽  
J. Parker Mickle
Keyword(s):  
Mr Imaging ◽  
Mass Effect ◽  
Intermediate Stage ◽  
Neurological Deficits ◽  
Blue Dye ◽  
Content Type ◽  
Vascular Proliferation ◽  
Peripheral Areas ◽  
Histopathological Studies ◽  
Fine Print

✓ To characterize the temporal course of radiosurgical lesions, 19 cats were irradiated in an animal linear accelerator radiosurgical device. The animals were followed clinically and, at 3.5, 6, 12, 18, 23, 29, and 63 weeks, were studied with gadolinium-enhanced magnetic resonance (MR) imaging. They were then sacrificed after Evans blue dye perfusion, and gross pathological and histopathological studies were performed. Mild neurological deficits developed between 3.5 and 4.5 weeks, correlating with the onset of mass effect both grossly and radiographically and with the maximum amount of white matter edema on T2-weighted MR imaging and microscopic examination. Clinical improvement occurred within several weeks as these resolved. The lesions were of similar size at all time intervals. Gadolinium-enhanced MR imaging demonstrated lesions with peripheral areas of enhancement and central nonenhancing regions which correlated histologically with areas of vascular proliferation and radiation necrosis, respectively. In the early lesions at 3.5 and 6 weeks, necrosis and edema were predominant. From 12 to 29 weeks, an intermediate stage was observed, with resorption of the necrotic debris as evidenced by progressive cavitation and microglial response and by increased perilesional vascularity. At 63 weeks, resorption was still taking place, but gliosis and diminution of the vascular response were seen.

Gamma knife radiosurgery in the management of cavernous sinus meningiomas

2000 ◽  
Vol 93 (supplement_3) ◽  
pp. 68-73 ◽  
Author(s):  
Pierre-Hugues Roche ◽  
Jean Régis ◽  
Henry Dufour ◽  
Henri-Dominique Fournier ◽  
Christine Delsanti ◽  
...  
Keyword(s):  
Mr Imaging ◽  
Tumor Growth ◽  
Gamma Knife ◽  
Cavernous Sinus ◽  
Gamma Knife Radiosurgery ◽  
Surgical Removal ◽  
Content Type ◽  
Cavernous Sinus Meningioma ◽  
The Mean ◽  
Fine Print

Object. The authors sought to assess the functional tolerance and tumor control rate of cavernous sinus meningiomas treated by gamma knife radiosurgery (GKS). Methods. Between July 1992 and October 1998, 92 patients harboring benign cavernous sinus meningiomas underwent GKS. The present study is concerned with the first 80 consecutive patients (63 women and 17 men). Gamma knife radiosurgery was performed as an alternative to surgical removal in 50 cases and as an adjuvant to microsurgery in 30 cases. The mean patient age was 49 years (range 6–71 years). The mean tumor volume was 5.8 cm3 (range 0.9–18.6 cm3). On magnetic resonance (MR) imaging the tumor was confined in 66 cases and extensive in 14 cases. The mean prescription dose was 28 Gy (range 12–50 Gy), delivered with an average of eight isocenters (range two–18). The median peripheral isodose was 50% (range 30–70%). Patients were evaluated at 6 months, and at 1, 2, 3, 5, and 7 years after GKS. The median follow-up period was 30.5 months (range 12–79 months). Tumor stabilization after GKS was noted in 51 patients, tumor shrinkage in 25 patients, and enlargement in four patients requiring surgical removal in two cases. The 5-year actuarial progression-free survival was 92.8%. No new oculomotor deficit was observed. Among the 54 patients with oculomotor nerve deficits, 15 improved, eight recovered, and one worsened. Among the 13 patients with trigeminal neuralgia, one worsened (contemporary of tumor growing), five remained unchanged, four improved, and three recovered. In a patient with a remnant surrounding the optic nerve and preoperative low vision (3/10) the decision was to treat the lesion and deliberately sacrifice the residual visual acuity. Only one transient unexpected optic neuropathy has been observed. One case of delayed intracavernous carotid artery occlusion occurred 3 months after GKS, without permanent deficit. Another patient presented with partial complex seizures 18 months after GKS. All cases of tumor growth and neurological deficits observed after GKS occurred before the use of GammaPlan. Since the initiation of systematic use of stereotactic MR imaging and computer-assisted modern dose planning, no more side effects or cases of tumor growth have occurred. Conclusions. Gamma knife radiosurgery was found to be an effective low morbidity—related tool for the treatment of cavernous sinus meningioma. In a significant number of patients, oculomotor functional restoration was observed. The treatment appears to be an alternative to surgical removal of confined enclosed cavernous sinus meningioma and should be proposed as an adjuvant to surgery in case of extensive meningiomas.

Thalamic lesions produced by gamma thalamotomy for movement disorders

2002 ◽  
Vol 97 ◽  
pp. 600-606 ◽  
Author(s):  
Chihiro Ohye ◽  
Tohru Shibazaki ◽  
Jie Zhang ◽  
Yoshitaka Andou
Keyword(s):  
Mr Imaging ◽  
Involuntary Movement ◽  
Gamma Knife Radiosurgery ◽  
Target Point ◽  
High Signal ◽  
Thalamic Lesion ◽  
Content Type ◽  
Stereotactic Thalamotomy ◽  
Thalamic Lesions ◽  
Fine Print

Object. The treatment of Parkinson disease and other kinds of involuntary movement by gamma knife radiosurgery (GKS) is presented. This is an extension of previous work. The clinical course and thalamic lesions were the main factors examined. Methods. Seventeen new cases were added to the previously reported 36 cases. The course and results for the whole series of 53 patients were examined. Treatment was undertaken using a single 4-mm collimator shot to deliver 130 Gy to the target. The target was determined in the previously treated patients by using classic methods involved in conventional stereotactic thalamotomy with microrecording. More recently, target localization has been performed by relating the target point to the total length of the thalamus. Points may then be defined as percentages of that length measured from the anterior pole. Targets can then be determined in relationship to the appropriate percentage. Thirty-five patients have been followed for more than 2 years and the longest follow up was 8 years. Two kinds of thalamic lesion were seen after GKS. Volumetric analysis on MR imaging revealed that the larger lesion was 400 to 500 mm3 at the beginning and gradually decreased in size. The smaller lesion occupied approximately 200 mm3 and also shrank over several months. Eighty percent of the treated cases showed good results and no significant complications, with the tremor subsiding at 1 year (Type 1). Several cases deviated from this standard course in four different ways (Types 2–5). If tremor persisted, conventional stereotactic thalamotomy with microrecording was performed. During such operations, normal neuronal activity was recorded from the region adjacent to the GKS thalamotomy target. This was the region showing a high signal on MR imaging. The activity patterns included the rhythmical grouped discharge of tremor rhythm. Conclusions. Gamma thalamotomy for functional disorders is still under development, but because the results with careful target planning are satisfactory, there are grounds for increasing optimism.

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