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The treatment of small to medium sized vestibular schwannomas (VS) with Gamma Knife (GK) stereotactic radiosurgery is a well-documented treatment alternative to surgical resection, with prospective nonrandomized trials demonstrating facial nerve and hearing preservation rates favoring GK over microsurgery 1,2 . Tumor control rates have been described upwards of 94% in recent literature, with acceptable complication rates 3 when compared to microsurgery. Long term actuarial resection-free control rates have been documented at 98.3% [4][5][6] , emphasizing the lasting effect post-GK. Larger VS pose a difficult clinical challenge, with many authors favoring surgical resection due to concerns around radiation dosing and side effects. Differing recommendations currently exist in the literature in terms of the degree of resection. Recently, the suggestion of sub-total resection in order to reduce the volume to one more amenable to GK has arisen. ABSTRACT: Object: To review our institutional experience with Gamma Knife (GK) stereotactic radiosurgery in treating large vestibular schwannomas (VS) of 3 to 4 cm diameter. Methods: We conducted a retrospective cohort review of all patients treated with GK for VS at our institution between November 2003 and March 2012. Data on age, sex, VS volume, location and maximal diameter, House-Brackmann (HB) facial nerve scores pre and post-GK, Gardner-Robertson (GR) hearing score pre and post-GK, GK treatment parameters, VS response time, complications and clinical outcome was recorded Results: A total of 28 patients during the defined time period were identified. Three patients were lost to follow-up. Mean follow-up was 34.5 months. Tumor control occurred in 92%, and was maintained in 85.7% at two years. Facial nerve or hearing preservation occurred in all treated compared to pre-GK status, as per HB and GR grading. Transient complications occurred in 80%. Temporary vestibular dysfunction occurred in seven patients (28%). One patient (4%) had the permanent complication of worsening pre-GK hemifacial spasm. Four patients (16%) developed hydrocephalus post-GK. Conclusion: GK stereotactic radiosurgery as a primary treatment modality for large VS can provide acceptable tumor control rates with good facial nerve and hearing preservation, and low complication rates.RÉSUMÉ: Radiochirurgie par scalpel gamma dans les schwannomes vestibulaires de grande taille. Objectif : Le but de l'étude était de revoir notre expérience institutionnelle de l'utilisation de la radiochirurgie stétéotaxique par scalpel gamma (SG) dans le traitement des schwannomes vestibulaires (SV) de grande taille, soit de 3 à 4 cm de diamètre. Méthode : Nous avons effectué une revue rétrospective de cohorte de tous les patients traités par SG pour un SV dans notre institution entre novembre 2003 et mars 2012. Les données sur l'âge, le sexe, le volume du SV, sa localisation et son diamètre maximal, les scores à l'échelle de House-Backmann (HB) pour le nerf facial avant et après traitement par le SG, le score à l'échelle de Ga...

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Intracerebroventricular (i.c.v.) administration of human atrial natriuretic factor (ANF), fragment 1-25, in the dose range 3 to 20 micrograms/kg did not alter resting arterial pressure or heart rate in rats anesthetized with chloralose/urethan (60:600 mg/kg i.p.), while angiotensin II (ANG II), 1 microgram/kg, produced a significant increase in arterial pressure after i.c.v. application. This pressor effect induced by ANG II was abolished by simultaneous administration of ANF (3 micrograms/kg i.c.v.). In isolated strips of rabbit aorta preconstricted with ANG II (10 nM), ANF caused a dose-dependent relaxation. In intact rats, the increase in blood pressure following intravenously administered ANG II (0.1 and 1 microgram/kg) was not altered by the highest dose of ANF (20 micrograms/kg) given intracerebroventricularly. These results suggest that atrial peptides may play an important role in the regulation of blood pressure by interacting with both the central and peripheral actions of ANG II. Inhibition of the central pressor action of angiotensin by ANF appears to be independent of any direct peripheral effect of the atrial peptides.