Spectral phonon scattering from sub-10 nm surface roughness wavelengths in metal-assisted chemically etched Si nanowires.

Frequency dependence in phonon surface scattering is a debated topic in fundamental phonon physics. Recent experiments and theory suggest such a phenomenon, but an independent agreement between the two remains elusive. We report low-temperature dependence of thermal conductivity in silicon nanowires fabricated using a two-step, metal-assisted chemical etch. By reducing etch rates down to 0.5 nm/s from the typical >100 nm/s, we report controllable roughening of nanowire surfaces and selectively focus on moderate roughness scales rather than the extreme scales investigated previously. This critically enables direct comparison with perturbation-based spectral scattering theory. Using experimentally characterized surface roughness, we show that a multiple scattering theory provides excellent agreement and explanation of the observed low-temperature dependence of rough surface nanowires. The theory does not employ any fitting parameters. A 5-10 nm roughness correlation length is typical in metal-assisted chemical etching and resonantly scatters dominant phonons in silicon, leading to the observed ~T(1.6-2.4) behavior. Our work provides fundamental and quantitative insight into spectral phonon scattering from rough surfaces. This advances applications of nanowires in thermoelectric energy conversion.

[Cerebral cavernomas, epilepsy and seizures. Natural history and therapeutic strategy]. / Cavernomes intracrâniens, épilepsie et crises d'épilepsie. Histoire naturelle et modalités thérapeutiques.

PURPOSE: To review, from a retrospective series of 48 patients presenting with seizures associated with one or more supratentorial cavernoma(s), the natural history of the seizures and outcome according to medical and surgical treatment. METHODS: Patients were divided into two groups: group A included patients presenting with a single seizure or rare seizures (n=21), and group B patients having intractable epilepsy (n=27). All received antiepileptic drugs and 35 were operated on (12 in the group A and 23 in the group B). Stereo-EEG was performed in 8 patients in group B. Surgery included lesionectomy alone (n=16), resection of the cavernoma and perilesional tissue (n=7) or tailored corticectomy including the cavernoma (n=12). RESULTS: The natural history of seizures was different in the two groups: mean age at seizure onset was 25 years in group B and 33 years in group A (p<0.05), seizures were partial in all patients in group B and 8 patients in group A (p<0.05). Seizure frequency and periodicity also varied. Prolonged seizure-free periods were observed. The cavernoma was temporal in 17 patients in group B and 4 patients in group A (p<0.01). In group A, seizure outcome was favorable following surgery or with antiepileptic medication only (7 patients out of 12 operated were seizure-free, as were 5 out of 7 non-operated). In group B, seizure outcome was better after surgery than with medication only (17 patients out of 23 operated were in Engel's Class I, while 3 patients of 4 non-operated patients had persisting seizures despite antiepileptic polytherapy). CONCLUSION: Variations in seizure severity in patients harboring cavernomas suggest different therapeutic approaches. In case of unique or rare seizures, surgical resection of the cavernoma is appropriate, but benefits of surgery over antiepileptic medication in terms of seizure control remains unclear. Intractable epilepsy associated with cavernomas is better controlled after surgery rather than with medication only. In these patients, a detailed preoperative work-up is necessary and should be followed by wide resection associated or not with corticectomy, especially in the temporal lobe. Evaluation of outcome after surgery should consider the surgical strategy, antiepileptic medications and the patient's seizure history.

[Hemorrhage in arteriovenous malformations: clinical and anatomic data]. / L'hémorragie dans les malformations artério-veineuses cérébrales.

BACKGROUND AND PURPOSE: Potential severity of hemorrhage often leads to treat a cerebral arteriovenous malformation. Consequences can be very various and serious. Our first purpose is to define the different types of hemorrhage. Our second purpose is to appreciate more precisely individual hemorragic risk of a cerebral arteriovenous malformation with the study of his angioarchitecture. We performed a prospective study in order to validate a logistic model and a classification previously described. PATIENTS: and method. From the whole series of 705 patients, 57% (n=394) suffered a parenchymal, subarachnoid or ventricular hemorrhage. Logistic model and classification of the hemorrhagic risk were prospectively tested on a consecutive population of 78 patients. Comparisons of theorical (calculated hemorrhagic risk) and real (hemorrhage or not) were performed by non parametric tests. RESULTS: Characteristics and clinical consequences of the hemorrhage were analyzed. Results of the prospective study confirmed data of the classification and showed a hemorrhage risk increasing with the grade: grade Ia 0%, grade Ib 30%, grade II 44%, grade III 57%, grade IV 88%. CONCLUSION: The study of the angioarchitecture of a cerebral arterio-venous malformation allowed to assess with accuracy his individual hemorrhagic risk. However, this precision may be improved by the study of other parameters of intracranial arteriovenous malformation.

[Characteristics of epileptic seizures associated with cerebral arteriovenous malformations]. / Caractéristiques des crises d'épilepsie associées aux malformations artério-veineuses cérébrales.

PURPOSES: The purpose of this study is to analyze the characteristics of epileptic seizures associated with cerebral arteriovenous malformations treated by radiosurgery. PATIENTS AND METHODS: Seven hundred and two patients are studied (406 men, 296 women) with a mean age of 33 when radiosurgery was performed. 210 patients had epileptic seizures; those seizures either uniquely revealed the arteriovenous malformation or were associated with other clinical signs. Seizures occurring after an hemorrhage were excluded from the study. We studied the age category upon seizures occurrence, the malformation localization, type of seizure (partial, generalized, or partial secondary generalized), the history related to the epileptic seizures, the clinical topographical correlation, the number of seizures, their duration prior to the radiosurgery, antiepileptic treatment provided, electroence-phalographic characteristics, angiographic characteristics, prior endovascular or surgical treatment, and factors associated with severe seizure. RESULTS: Epileptic seizures revealed the arteriovenous malformations in 30% of the cases; they predominated between 10 and 40 years (80.5%) with a peak between 20 and 30 years. The malformation localization most frequently associated with seizures were temporal and rolandic for partial seizures, whereas frontal or sylvian localization were predominantly associated with generalized seizures. The type of seizure was, in all cases, related to the malformation localization because of the initial signs seizure. 47.6% of the patients showed a limited number of seizures (between 2 and 20), 27.6% showed only a single seizure, and 24.7% suffered from severe epilepsy. Generalized seizures are unique in the majority of cases (61.8%) whereas partial seizures were severe in 47.6% of the cases. The majority of patients are under a single-drug therapy (79%). The EEG patterns showed a small increase of slow and sharp localized waves in patients presenting seizures compared with the global population (27% and 15% respectively). Severe seizures predominated between 10 and 19 years of age; seizures were exclusively partial in 59.6% of the cases and secondary generalized in 40.4%, their frequencies were between 1 to 4 per month in the majority of cases (59.1%), the delay was often more than 10 years (57.7%), status epilepticus was rare (5.8%), temporal and rolandic localization were predominant, social and professional insertion of the patient was preserved in 87.5% of the cases, and seizures did not provoke any death. The angiographic characteristics associated with seizures were: superficial localization, volume, superficial venous drainage, recruitment and venous divergence. CONCLUSION: Anatomic and topographic characteristics of cerebral arterio-venous malformations may provide information on the features of seizures associated with them.

[Characteristics of headache associated with cerebral arteriovenous malformations]. / Caractéristiques des céphalées associées aux malformations artério-veineuses cérébrales.

BACKGROUND: and purposes. The purpose of this study was to identify the specific characteristics of headaches associated with cerebral arteriovenous malformations in order to differentiate them from other known entities of headaches such as migraine, cluster headache, and trigeminal neuralgia. This differentiation allows an early diagnosis of cAVM and a treatment to be administrated before any cerebral hemorrhage. PATIENTS AND METHODS: The study included 700 patients with cAVM and treated by radiosurgery. Out of this series, only 109 (48 males, 61 females, mean age of 33) presented with headaches. Headaches were studied as a possible revelation mode of a cAVM, either as an isolated sign, preceding an epileptic seizure, a cerebral hemorrhage, or associated with a neurological deficit. Analysis concerned 13 clinical parameters and 30 anatomic parameters based on angiography. RESULTS: Headaches were found in 15.6%; they were isolated in 6%. They preceded a cerebral hemorrhage in 12.6%, constituting an early alarm signal when increasing in intensity, frequency and duration. They were associated with seizures or a neurological deficit in 9.6%. We found a predominant female sex-ratio (0.78) and occurrence at a young age (72.3% between 10 and 40 years). Headaches were non-pulsating in 95.3%; nausea, vomiting, light or sound phobia were only found in 4.7%. Headaches were unilateral and homolateral to the malformation in 80%, corresponding to the malformation topography in 97.4% in posterior location and 80% in anterior location. Associated neurological symptoms existed in 20.2%; related to the malformation and lasting 5 to 30 minutes. Duration of pain episodes was less than 3 hours in 77% with a frequency of 1 to 2 per month in 82.5%. Pain was mild and responded to simple analgesics. A family migraine was found in only 3 patients. The angiographic characteristics of the malformations were meningeal afferences, superficial venous drainage and posterior location. CONCLUSIONS: Headaches associated with cerebral arterio-venous malformations form a distinct category that can be determined from specific characteristics; this should help an early diagnosis of cerebral arterio-venous malformations in order to start a treatment before the occurrence of cerebral hemorrhage.

[Progressive neurological deficits in cerebral arteriovenous malformations]. / Les déficits neurologiques progressifs dans les malformations artério-veineuses cérébrales.

Progressive neurological deficits are uncommonly associated with cerebral arteriovenous malformations. We present 25 cases (3.54%) from our series of 705 patients treated by radiosurgery. Common characteristics were preferentially: large cerebral arteriovenous malformations, arterial steal, arterial recruitment, venous reflux and deep location. After multivariate analysis, only arterial steal was significantly associated with neurological deficits. Course after treatment was variable and correlated with cerebral arteriovenous malformations regression. Different pathophysiologic hypotheses and their therapeutic consequences are discussed.

[Hemorrhage after radiosurgery of cerebral arteriovenous malformations]. / Hémorragie après radiochirurgie des malformations artério-veineuses cérébrales.

BACKGROUND AND PURPOSE: Obliteration is progressive after radiosurgery of cerebral arteriovenous malformations. Thus the hemorrhage risk still remains until obliteration. Purposes of this study are to appreciate severity of post-radiosurgery hemorrhages, actuarial risk of hemorrhage and parameters associated with it. PATIENTS: and method. Over 705 patients treated, 46 (6.5%) had one or several hemorrhages. Clinical, anatomic, dosimetric parameters and obliteration rates before hemorrhage were studied. Then, actuarial risks per patient and per hemorrhage were calculated. Correlations between parameters and risk were searched by uni and multivariate analysis by drawing hemorrhage-free survival curves (limit-product Kaplan-Meier) and Cox model. RESULTS: Except one pure ventricular hemorrhage causing death of one patient, only parenchymal hemorrhages were associated with morbidity (80% of cases with 45% of permanent deficits). Overall mortality rate by hemorrhage was 6.5%. Overall morbidity rate was 34.8% and 13.6% for permanent deficit. Mean obliteration rate before hemorrhage was 25%. Actuarial hemorrhage rate were 2.98% per patient and 3.24% per hemorrhage. Actuarial rate per patient increased from 1.46% first year to 5.95% 4(th) year after radiosurgery. Parameters correlated with hemorrhage risk were in univariate analysis size (p=0.01), Spetzler and Martin's grade (p<0.001), dose to reference isodose (p=0.03), Dmin (p=0.08), intra or paranidal aneurysms (p<0.001), and recoverage (p<0.001). After multivariate analysis, only intra or paranidal aneurysms, recovering and Dmin were significantly associated with hemorrhage-free survival after RS. CONCLUSIONS: Post-radiosurgery hemorrhages are often sum of hemorrhage risk factors of the cerebral arteriovenous malformation and factors predicting low rate of obliteration. They can be in some cases foreseen but rarely avoided.

[Evolution of epileptic seizures associated with cerebral arteriovenous malformations after radiosurgery]. / Evolution des crises d'épilepsie associées aux malformations artério-veineuses cérébrales après traitement par radiochirurgie.

The goal of this study is to evaluate the response of epileptic seizures associated with cerebral arteriovenous malformations following radiosurgery and determine the factors associated with a positive outcome. The series included 210 patients (123 men, 87 women) with a mean age of 33. One hundred seventy three patients out of 210 were controlled after radiosurgery. Seizures completely disappeared in 58% of cases and decreased in 18%. Anti-epileptic treatment was stopped in 44%. Sex and age upon seizure appearance were not found as determining factors in patients whose seizures disappeared after radiosurgery. Generalized seizures disappeared following radiosurgery in 90.7%, partial secondary generalized seizures in 53.5%, and partial seizures in only 39.6%. Frontal or temporal malformations are associated with a better response after radiosurgery than sylvian or rolandic location. Seizure disappearance was maximal in case of isolated seizure prior to the radiosurgery (84.4%), was reduced to 61.2% when seizures were limited to 2 to 20, and disappeared in 21.4% in severe seizures. Epilepsy present less than 3 years prior to radiosurgery disappeared in 71.9%; was reduced to 45% when the delay was over 3 years. Seizures disappeared in 64.4% when the malformation was obliterated, they were reduced to 46.9% when malformations persisted. The persistence of severe seizures following radiosurgery was linked to persistence of the malformation. On the other hand early seizures occurred in 3.3% during the first 48 hours following radiosurgery; they disappeared in 72.2% after that period. De novo seizures also occurred in 1.7% and disappeared in all these cases. In conclusion, seizures associated with cerebral arteriovenous malformations respond well to radiosurgery; the malformation obliteration evokes its association with the seizure; the seizure disappearance in spite of persistence of the malformation evokes the positive effect of radiotherapy on epileptic seizures.

[Course of headaches associated with cAVMs after radiosurgery]. / Evolution des céphalées associées aux malformations artério-veineuses cérébrales après radiochirurgie.

The purpose of this study is to evaluate the response of headaches associated with cerebral arteriovenous malformations following radiosurgery and determine the factors that are associated with a positive outcome. From our series of 700 patients whose cAVM was treated by radiosurgery, this study includes 109 patients (48 males, 61 females) with a mean age of 32 when radiosurgery was performed. Headaches resolved in 37 patients (53.7%), decreased in 14 patients (20.3%), persisted in 16 patients (23.2%), and even increased in frequency in 2 (2.9%). Headaches disappeared 2 years following radiosurgery in the majority of patients (31 out of 37: 83.3%). The disappearance rate of headaches was better when it was the only sign of the malformation (64%) or preceded an epileptic seizure (60%) with respect to the case when it preceded cerebral hemorrhage (34.8%). Headaches having the best response were those with 1 to 2 episodes per month (64.9%) and whose episode duration was less than 3 hours (67.6%). Unilateral headaches accounted for 86.5% of resolved headaches whereas bilateral headaches were only 8.1% and even less were the diffuse ones (5.4%). The best evolution was obtained for those associated with a parietal location of the cerebral arteriovenous malformation, followed by rolandic (respectively 55.5% and 50%). Occipital malformation was associated with headache disappearance in 38.1% and temporal with 34.3%, whereas frontal location was associated with headache disappearance in only 25% of the cases. Headache disappearance was often correlated with cerebral arteriovenous malformation outcome after radiosurgery (64.9% of disappearance in case of complete obliteration). However, in 24.8%, headaches disappeared prior to the malformation obliteration and were associated with a decrease of the flow, of the nidus volume or with the nidus disappearance with the persistence of a precocious venous drainage. Headaches disappeared in spite of the malformation persistence in 5.4% of the cases. We found de novo headaches in one patient one year following RS. Another patient presented an episode of headache 12 hours following RS. The course of headaches associated with cerebral arteriovenous malformations after radiosurgery is positive in the majority of cases and correlated to the malformation outcome. This correlation suggests a link between cerebral arteriovenous malformations and headaches and the equal benefit of radiosurgery on both of them.

[Parenchymal changes after radiosurgery of cerebral arteriovenous malformations. Clinical and MRI data]. / Réactions parenchymateuses après radiochirurgie des malformations artério-veineuses cérébrales. Données cliniques et IRM.

BACKGROUND AND PURPOSE: Purposes of this study are to describe different parenchymal changes seen after radiosurgery of cerebral arteriovenous malformations and the clinical symptoms which can be associated, and risk factors correlated with them. PATIENTS: and method. From the whole population of 705 patients with a cerebral arteriovenous malformations treated by radiosurgery between 1984 and 1998, clinical from 615 patients and post radiosurgery MRI data from 367 patients were reviewed. Neurological deficit occurred in 5.37% of cases and was still persistant in 1.46% of cases. Delay of occurrence of deficits ranged from 6 to 83 months (mean: 27 months, median: 15 months). Parenchymal changes seen in MRI were classified in 4 grades: 1 without parenchymal changes, 2 hypersignal in sp T2, 3=2 with homogenous enhancement with gadolinium, 4 with hyposignal in spT1 and annular irregular enhancement. Several parameters (size, volume, angioarchitecture of the cerebral arteriovenous malformation, dosimetric parameters) were studied and correlations were searched by uni and multivariate analysis with occurrence and delay of occurrence of deficits or parenchymal changes. RESULTS: In multivariate analysis, only size was significantly correlated with occurrence of parenchymal changes (p=0.0016); only size of the malformation was significantly correlated with delay of occurrence of parenchymal changes (p=0.0082); only grade 4 was correlated with occurrence of neurological deficit (p<0.00001). However, when only "a priori" parameters (known before radiosurgery) are introducted in logistic model, size taille (p=0.02) and hypoplasy of a sinus (p=0.0049) are significantly correlated with occurrence of neurological deficit. Only parenchymal changes grade 4 was significantly correlated with delay of occurrence of a neurological deficit (p<0.00001). However, when only a priori parameters (known before radiosurgery) are introducted in logistic model, only arterial steal (p=0.054) was significantly correlated with delay of occurrence of a neurological deficit. CONCLUSION: Parenchymal changes are various in expression, signification and clinical symptoms associated with them. They must be known and recognized for better prevention and symptomatic treatment as well.

[Radioanatomy of cerebral arteriovenous malformations]. / Radioanatomie des malformations artérioveineuses cérébrales.

New imaging modalities permit detailed knowledge of the anatomy of cerebral arteriovenous malformations. Magnetic resonance imaging (MRI) provides morphological data, size and topography of the nidus, anatomic relationship, as well as dynamic information particularly with the use of MR angiography. Selective and hyperselective cerebral angiography provide information about the angioarchitecture and search for associated vascular abnormalities such as aneurysms. It is therefore possible to distinguish malformations associated with a high risk of hemorrhage and to define the indications for radiosurgery.

[Stereotaxic radiotherapy of cerebral arteriovenous malformations: the role of neuroradiology]. / Radiothérapie stéréotaxique des malformations artério-veineuses cérébrales: place de la neuroradiologie.

The therapeutic approach to cerebral arteriovenous malformations has been modified with the availability of stereotactic radiosurgery, initially, the main indications of radiosurgery were limited, non surgical arteriovenous malformations. Indications are now much more diverse. Imaging plays an important role in the radiosurgical management of arteriovenous malformations and its evaluation. In this review, the different roles of neuroimaging are discussed; characterization of malformations, choice of the best indications, role of embolization, delimitation of the target, evaluation of results and complications of radiosurgery.

Parenchymal changes after radiosurgery of cerebral arteriovenous malformations. Preliminary report of a proposed classification.

Radiosurgery of cerebral arteriovenous malformations (cAVM) can induce parenchymal changes seen on MRI. The purpose of this study was to classify these changes and to correlate them to clinical outcome and obliteration of the cAVM. 142 patients with cAVM underwent radiosurgery with a linear accelerator between 1994 and 1995. 60 clinical records, MR images, and postradiation angiograms were reviewed. Signal abnormalities and contrast enhancements were correlated with clinical deterioration and size decrease of the AVM. The Spearman nonparametric test was used for statistical correlation. MR findings allowed to differentiate between four grades: grade 1 = no parenchymal changes; grade 2 = hypersignal on T2-weighted sequences, grade 3 = grade 2 + contrast enhancement on T1-weighted sequences; grade 4 = grade 3 + central hyposignal (necrosis-like) + peripheral hyposignal surrounding the AVM on T1-weighted sequences. Grade 4 was significantly related (p < 0.001) to clinical deterioration (deficit, seizures, increased intracranial pressure). All grade 4 patients, and only them, had clinical symptoms. Most of these symptoms regressed with corticoid treatment. Grade 4 was also related to the proportion of obliteration of the cAVM at 1 year after radiotherapy: mean proportion of obliteration was 12.5% for grade 2, 25% for grade 3 and 82.2% for grade 4 (p < 0.01). The size of T2-weighted MR images was related to clinical symptom appearance (p < 0.001). Finally, contrast enhancement was not predictive of the occurrence of the clinical symptoms. This proposed classification allows one to differentiate between the various MR images, and seems to predict clinical complications and response to radiotherapy of the cAVM.

Inter-ictal brain SPET in frontal epilepsy: correlations with stereo-electroencephalography.

Single photon emission tomography (SPET) imaging holds promise for localization of the site of extratemporal seizures, but limited data currently exist; in particular, correlations with stereo-electroencephalography (S-EEG) have not been made. Ten patients aged 14-44 years (mean 25 years) with a proven frontal or central epilepsy by S-EEG and post-surgical follow-up were studied retrospectively: 7 patients had frontal cortectomy and one patient had a callosotomy for bifrontal epilepsy. All patients underwent clinical, inter-ictal and ictal video-EEG, computed tomography scan and/or magnetic resonance imaging, SPET and S-EEG examinations. SPET was performed inter-ictally, while on usual epileptic medications, using 99Tcm-HMPAO (n = 4) or 123I-IMP (n = 6) as the perfusion tracer. The SPET images were evaluated independently by two observers, blind to any data other than the diagnosis of frontral or central epilepsy. Localization of inter-ictal SPET hypoperfusion was compared with the epileptogenic (EZ), irritative (IZ) and lesional (LZ) zones, as defined by S-EEG. Six patients showed structural frontal abnormalities. One patient had normal SPET and one had a contralateral hypoperfusion. Therefore, concordance of sides was found in 8 of 10 patients (including one with bilateral SPET and S-EEG abnormalities). The hypoperfusion was equal to or larger than the EZ + IZ + LZ in 6 patients (5 had a frontal lesion). SPET hypoperfusion was smaller than the EZ in one patient, and different from the EZ, IZ and LZ in two patients. Although this was a retrospective study, it provides qualitative data regarding the significance of inter-ictal SPET abnormalities in frontal or central epilepsy.(ABSTRACT TRUNCATED AT 250 WORDS)