1. Imaging of radiosurgical planning and follow-up of arteriovenous malformations treated by gamma knife: ten years experience. P.David*, N.Massager**, N.Sadeghi*, P.Jissendi*, D.Balériaux*, I. Delpierre*, B.Lubicz*. * Neuroradiology Clinic **Gamma knife Unit Erasme hospital Université Libre de Bruxelles Brussels, Belgium

2. Purpose To define the respective role of conventional MRI (MRI), MR dynamic substracted angiography (MRDSA) and digital substracted angiography (DSA) in the planning and follow-up of AVM treated by gamma knife(GK).

3. Background - Arteriovenous malformations (AVMs) : important indication for radiosurgery - Digital substracted angiography (DSA) “gold standard “ accurate delineation of the nidus - DSA: “gold standard “ for the evaluation of the treatment efficiency - DSA invasive procedure / inherent risks

4. Background - Magnetic resonance angiography (MRA): Time of flight (TOF) / Phase contrast angiography (PCA) → excellent spatial resolution images / no temporal resolution. -Time resolved Magnetic Resonance Digital Substracted Angiography (MRDSA) good temporal resolution. - Usefulness of MRDSA for planning and follow- up of AVMs after gamma knife radiosurgery. - 3D MRSA / 2D MRSA

5. Material and Methods - N=189 - Between January 2000 and December 2009, 189 patients were treated for arteriovenous malformation in our Gamma Knife Centre - Patients were prospectively studied before GK radiosurgery treatment and followed at 12, 24 and 36 months or more by MRI, MRA and 2DMRDSA - Nidus Flow was analyzed - When complete obliteration was suspected by MRDSA during follow-up, DSA was then performed for confirmation of the complete obliteration

6. Results - MRDSA allowed to study both size and dynamic evolution of the flow in the nidus GKS planning : N=189 - Follow-up ( Erasme / ULB MR unit) : N= 65

7. Results - The obliteration rate was 95% - Period of 6 months to 5 years (mean period 2.1 years) - Transient neurological symptoms appeared after treatment in 7 patients (13%) - Permanent neurological worsening was observed in 3 patients (5.7%)

8. Day of treatment

9. 6 Months

10. Year 1

11. Year 2

12. Year 3

13. Day of treatment

14. Year 2,5

15. Discussion - MRDSA : technique derived from Contrast Enhanced Magnetic Resonance Angiography (CE MRA) CE MRA : acquisition of a heavily T1W GE sequence { short TR/TE ( 30°) } precisely timed after a bolus administration of a Gd chelate > strong saturation of the tissue signal while blood T1 is artificially decreased by a Gd injection  vascular hypersignal - With a good temporal resolution of 2 frames/second a real time substraction of a mask image can be applied on 2D or 3D projection images Wang et al, Magn Reson Med 1996

16. Discussion - GK radiosurgery : effective treatment in combination with embolisation in patients with intracranial AVMs - Residual AVMs carry a risk of haemorrhage  follow-up studies are required to confirm complete obliteration - MRI and MRA can be used - to estimate the size of the nidus - to detect radiation-induced changes in patients with intracranial AVMs - 2MRDSA: provides additional hemodynamic information compared to (TOF/PCA/CE) MRA

17. Conclusions MRDSA : non invasive tool - dynamic evolution of the flow - nidus modifications size after GK surgery -2D in our series / 3D in others series of the literature Useful in association with MRI -Can be repeated as long as opacification of the nidus or early venous drainage persists DSA mandatory to confirm the complete occlusion at the end of follow-up