Gamma Knife Radiosurgery For AVM: Evaluation Of Different Prognostic Factors

Alberto Franzin1, Piero Picozzi, MD2, Francesco Scomazzoni3, Silvia Snider3, Carlo Serra3, Micol Valle3, Davide Milani3, Claudio Righi3, Franco Simionato3, Pietro Mortini3

1Milano, Italy 2Department of Neurosurgery, IRCCS San Raffaele 3IRCCS S. Raffaele, Milano/ Italia

Keywords: gamma knife, vascular malformation, arteriovenous malformation, outcome, radiosurgery

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     To assess the predictive prognostic factors for the closure of an AVM in patients undergoing stereotactic radiosurgery with Gamma Knife.
     A total of 127 patients were included in the study. The AVM were classified on the basis of neuroradiological data: Spetzler-Martin Degree I in 20 cases (15.7%), Degree II in 45 (35.4%), Degree III in 50 (39.4%) and Degrees IV-V in 9 (7.1%). The AVM occupied the deep structures (nuclei of the base, thalamus, brainstem) in 16.5% of patients.
     The peripheral prescription dose (periphery dose) was between 16-30 Gy, with an average dose of 22.3 Gy, using a prescription isodose of 50%. The volume of AVM varied, with an average level of 2.7 cc (0.1-13 ml).
      The average follow-up of patients undergoing cerebral angiography control was 44.9 months (median: 47.0 range 3-83). In 68 cases out of 104 (65%), the brain MRI or cerebral angiography showed a closure of the AVM. In 54 patients out of 90 (60%) complete obliteration was achieved (average closure time for the nidus, according to the angiographic exam was 48.5 months, range of 43.9-53.1 months).  In the univariate regression analyses, the presence of deep venous drainage correlates with a greater hemorrhagic risk at the beginning (p = 0.02). Most patients who experienced bleeding (8 out of 10 cases, 80%) had deep venous drainage. The age of patients was not statistically significant, the volume and the deeper seat gave a border-line value (p=0.07, p=0.08 respectively). The volume of the nidus ( p=0001), the dose (p0.004), the classification by Pollock-Flickinger in 2002 (p=0.031), considering the age, volume and location of the AVM, and his last revision in 2008 (p=0.025) were statistically significant in predicting the outcome (of the AVM closure). In the multivariate analysis after considering the age, type of venous drainage (superficial versus deep), the onset of bleeding, deep seat, only the volume of the AVM nidus was statistically significant (p0.01). Early and permanent complications were rare, according to the literature: radionecrosis (4.9%), permanent neurological deficits (6.6%), cystic formations (1.6%).
     This is a retrospective study.
     The high rate of obliteration, the low incidence of complications and haemorrhagic episodes encourage the use of radiosurgery in carefully selected cases.
     The volume of the nidus significantly influences the outcome of radiosurgery treatments and the Pollock-Flickinger classification system reflect greater accuracy in predicting the AVM closure in patients who are candidates for stereotactic radiosurgery.


Project Roles:

A. Franzin (), P. Picozzi (), F. Scomazzoni (), S. Snider (), C. Serra (), M. Valle (), D. Milani (), C. Righi (), F. Simionato (), P. Mortini ()