1. Cerebral Arteriovenous Malformations: The Simplicity of Routine MR Imaging & Conventional Angiogram for Follow-Up After Gamma-Knife-Radiosurgery
Carlos F. Weber MD, Linda J. Bagley MD, John Y.K. Lee MD, Michele Alonso-Basanta, Laurie A. Loevner MD, Kim O. Learned MD
University of Pennsylvania Health System
Philadelphia, PA
eEdE-61

2. Introduction
Gamma knife radiosurgery is a well-established option for the treatment of cerebral Arteriovenous Malformations (AVM).
Postradiosurgical MR imaging follow-up oftentimes is a diagnostic challenge due to the uncertainty of nidus obliteration, expected posttreatment change and complications.
We will offer the step-wise analysis and highlights the specifics to representative cases to enable the viewers to navigate through the complex pre- and post- radiosurgical imaging of cerebral AVM with ease.

3. Outline Review of imaging features of brain AVM
Spetzler-Martin Grading System
Principles of gamma knife radiosurgery, and patient selection criteria
Longitudinal follow-up after gamma knife radiosurgery with MR imaging and conventional angiogram
Correlation between the clinical status and/or complications with imaging findings of the irradiated nidus

4. Imaging Diagnosis of AVM
MRI and MRA
Conventional Angiography
“High Resolution MR images, supplemented by cerebral angiography are optimal for dose [and overall management] planning”.
AVM Management depends on the risk of subsequent hemorrhage, which is determined by the anatomical ( MRI, MRA and Angiography), historical and demographic features of the individual patient.
High resolution MR images, supplemented by cerebral angiography are optimal for dose planning. Niranjan, A. Et. al. Stereotactic Radiosurgery guideline for management of patients with intracranial Arteriovenous Malformations. Prog Neurosurg Basel Karger, 2013, vol 27, pp
Niranjan, A Prog Neurolog Surg (2013)

5. AVM: MR imaging
Classic tightly-packed “flow voids” mass best seen on T2
Minimal/no mass effect
Surrounding T2 hyperintense gliosis
Variable hemorrhage
Two differente cases of cerebral AVMs, the superior one has an identifiable nidus (glomerular type) while the inferior one is less defined, (diffuse and/or proliferative).
Carlos, split into 2 slides. May want to replace the FLAIR with T2 weighted to illustrates flowvoid. May need T2/GRE to show hemorrhage
Fig. 1: Axial T2 FLAIR demonstrates a large Grade 5 AVM in the left frontotemporal region (circle) with tightly packed vessels and preserved “flow voids” (arrow).

6. AVM: MR imaging Avid T1 contrast enhancement
Need MRA
Avid T1 contrast enhancement
MRA: depiction of high flow
Fig. 1: Redemonstrated.
Fig. 2: Coronal T1 Postcontrast demonstrate avid contrast enhancement.

7. AVM: MR imaging Diffuse or proliferative: large draining vein
Drawbacks: suboptimal delineation of AVM angioarchitecture
Two different cases of cerebral AVMs, the superior one has an identifiable nidus (glomerular type) while the inferior one is less defined, (diffuse and/or proliferative).
Fig. 3: Axial T2 shows a large serpiginous flow void corresponding to an abnormal vessel.

8. AVM: Angiography Gold Standard for Delineation of Angioarchitecture
Abnormal tangle of blood vessels
Enlarged feeding arteries
Identifiable nidus
Early venous drainage, bypassing parenchymal phase of contrast enhancement
Drawbacks: Invasive procedure, radiation, Iodine contrast nephropathy
Early angiographic phase with early venous opacification , consistent with A-V shunting.
Carlos, for best electronic powerpoint presentation, 1 or 2 images per slide and images should occupy at least half the slide surface, text should be 26
Fig. 4: Frontal right carotid angiography demonstrates a S-M Grade 4 AVM supplied by the MCA with superficial drainage (Yellow arrow).

9. Spetzler-Martin Grading System
Osborn. Diagnostic Imaging Brain
WOW!! ;)
Citation:
There are certain imaging and clinical features that are important in determining the safest treatment modality ( between surgery, embolization and radiosurgery)… however, the complication rate depends largely in the Spetzler-Martin grade: The higher (or lower) the grade , The higher (or lower) the complication rate. Therefore, patients with smaller and cortical-based brain AVMs are likely to benefit the most from surgical resection. Radiosurgery has a high cure rate with relatively low complication rates. However, its major limitation is that radiation is slow to take effect, it may take up to 2 years before any shrinkage of the brain AVM is seen. Therefore, radiosurgery may not be well suited for the treatment of brain AVMs with angiographic risk of haemorrhage.
Approach/Methods:Review of the Spetzler-Martin Grading system for brain AVM, the principles of gamma knife radiosurgery, and patient selection criteria will be highlighted, using clinical cases from a single institution over 10-year period. Postradiosurgical longitudinal imaging follow up of AVM will be discussed, with emphasis on the value of magnetic resonance imaging (MRI), magnetic resonance angiography (MRA) and angiography. The evolution of the treated nidus and the surrounding brain changes, complications and correlation of MR findings with angiogram are illustrated. Finally, the correlation between the clinical status with imaging findings will be included.
Illustration by Carlos F. Weber, MD
The Aneurysm and AVM Foundation -TAAFonline.org

10. Spetzler-Martin Grading System
Conventional Angiogram
High score  High Surgical risk

11. Principles of Gamma Knife Radiosurgery
Gamma Knife Radiosurgery delivers finely focused high dose radiation using radioactive Cobalt sources precisely to its target while causing little or no damage to the surrounding tissue.
The Gamma Knife is an advanced radiation treatment for small – medium size brain tumors and abnormal blood vessels called arteriovenous malformations and other neurological conditions,
Despite the name , GK isn’t a knife but is a machine that delivers a single , finely focused high dose radiation precisely to its target while causing little or no damage to the surrounding tissue.

12. Gamma Knife Radiosurgery for AVM Patient Selection Criteria
Compact lesions < 3 cm
Unfavorable surgical candidates: radiographically (Spetzler-Martin Grade >3) or existing comorbidities
Focal high dose to the nidus minimizes radiation of surrounding normal tissue  beneficial treatment for AVM in deep location, eloquent area
A. Niranjan. Prog Neurol Surg (2013)
Barr. Neurosurg Clin N Am (2012)

13. Left hemisphere AVM SM Grade 4
Location: Eloquent Language left temporal frontal parietal
Nidus Size: > 4 cm
Drainage: superficial (yellow arrowhead) and deep (red arrow)
Carlos, the GRE on the left shows old hemosiderin hemorrhage. I replace it with Flair to show parietal lobe
60-year-old man with end-stage renal disease diabetes hypertension seizure disorder left hemisphere AVM as well as multiple small intracranial aneurysms. The patient is scheduled for Gamma knife radiosurgery.
On left common carotid angiogram, dated 4/9/2008: There is a left-sided arteriovenous malformation supplied by branches of the middle cerebral artery. There is superficial drainage via vein of Labbe and deep venous drainage to the dural venous sinuses. There is an infundibulum at the origin of the branch of the middle cerebral artery seen best on the lateral view. The left A1 segment of the anterior cerebral arteries hypoplastic. There is no supply to the AVM via the left anterior cerebral artery.
Fig. 5: Left common carotid frontal and lateral angiographies demonstrate the AVM Nidus.
Fig. 6: Axial T2 and GRE MRIs demonstrate the S-M Grade 4 AVM (Circle). Notice on the GRE images the hemosiderin deposition from old haemorrhage.

14. Pre Vs Post Gamma Knife Radiosurgery
Pre Gamma Knife
AVM nidus in left sylvian fissure temporal frontal parietal lobe
Post Gamma Knife
Fig. 7: Axial T2 FLAIR and T1 Post C+
Axial FLAIR, axial T1 precontrast
Size: Greater than 4 cm
Location: None eloquent areas.
Venous drainage: Superficial.
S-M grade: 3-4
IMPRESSION: Left-sided temporal parietal lobe AVM supplied by left middle cerebral artery branches with superficial and deep venous drainage.
4-5 mm right ICA bifurcation aneurysm.
3-4 mm before meals ON aneurysm with hypoplastic left A1 segment of the anterior cerebral artery.
On preoperative MRA dated 5/1/2009: Redemonstrated 3.3 x 1.6 x 2.0 cm irregular tangle of vessels representing an AVM nidus centered about the left sylvian fissure involving the left temporal frontal and parietal lobes. It is supplied by an enlarged left middle cerebral artery. Drainage appear to be both deep and superficial into a markedly enlarged basal vein of Rosenthal as well as thin to multiple large cortical veins. It appears to be large venous varix measuring approximately 1.4 cm in the left sylvian fissure. No definite progression of hemorrhage.
Redemonstration of a 4 mm aneurysm in the right internal cerebral artery bifurcation projecting posteriorly, and a 2-3 mm aneurysm in the anterior communicating artery complex at the junction of the right A1 and A2 segments, projecting inferiorly also not significantly changed when compared to previous
Brain MRI dated 8/3/2010:
Redemonstrated is a triangle of flow void centered within the left perisylvian frontal lobe compatible with patient's known intracranial AVM. The nidus is not as clearly demonstrated as when compared to the prior examination dated 4/5/2008 now with significant development of surrounding FLAIR hyperintensities within the white matter extending focally into the overlying cortical gray matter.
Phase contrast MRV demonstrates a cluster of irregular vein centered at the region of the left frontal and the venous malformation. The venous drainage from this nidus appears isolated to the superficial venous system. No definite the venous drainage is identified. Although angiography has higher sensitivity for evaluation of the venous structures.
IMPRESSION: Left frontal arterial venous malformation appears smaller in size with decreased arterial and venous flow when compared to the prior examination. No definite deep venous drainage is identified. Cerebral edema surrounds the left frontal AVM centered within the adjacent white matter with some focal extension to the overlying gray matter cortex.
2 mm left to right midline shift.
Stable 4 mm right internal carotid artery aneurysm
Fig. 8: Axial T2 FLAIR and T2 demonstrate partial nidus regression and moderate surrounding high T2 signal. vasogenic edema, gliosis or hemorrhage.

15. Gamma Knife Radiosurgery for AVM Follow-up
Nidus obliteration
GK is slow to take effect: up to 2 years for shrinkage of the brain AVM
F/U Complications
Clinical and MR imaging follow-up intervals:
6 months for first 2 years after GK
Yearly afterward
Citation:
There are certain imaging and clinical features that are important in determining the safest treatment modality ( between surgery, embolization and radiosurgery)… however, the complication rate depends largely in the Spetzler-Martin grade: The higher (or lower) the grade , The higher (or lower) the complication rate. Therefore, patients with smaller and cortical-based brain AVMs are likely to benefit the most from surgical resection. Radiosurgery has a high cure rate with relatively low complication rates. However, its major limitation is that radiation is slow to take effect, it may take up to 2 years before any shrinkage of the brain AVM is seen. Therefore, radiosurgery may not be well suited for the treatment of brain AVMs with angiographic risk of haemorrhage.
Geiprasert et al. Radiographics 2010; 30: Radiologic Assessment of Brain Arteriovenous Malformations: What the Clinicians need to know.
Illustration by Carlos Weber, MD
Geibprasert Radiographics 2010

16. Follow-up after GK for AVM
Routine MR imaging follow-up is appropriate:
Higher cost-effectiveness
Accessibility and lower invasiveness compared to angiogram
Additional information of the surrounding brain
Conventional angiogram is indicated:
to confirm the obliteration of the nidus when nidus is not evident on MRI
to evaluate AVM recurrence/growth in patients with new clinical seizure, neurological symptoms, and acute hemorrhage
Reference;
Magnetic resonance imaging proved to be an accurate , noninvasive method for evaluating the patency of AVMs that where identifiable on MR imaging after stereotactic radiosurgery. This imaging modality is less expensive, more acceptable to patients and does not have the potential of neurological complications that may be associated with cerebral angiography. B.E. Pollock et al. J. Neurosurg. Vol 85 pp , 1996.
Magnetic resonance imaging is a sensitive in vivo method for detecting cerebral radiation injury. MRI offers a method for evaluating the regression of arteriovenous malformations nidus, but the complete obliteration of the nidus after radiosurgery still relies on the angiogram. “W-Y Guo, et al.”Gamma Knife radiosurgery of cerebral arteriovenous malformations. Int. J. of Radiation oncology Biol. Phys. Vol 25. pp
B.E. Pollock et al. J. Neurosurg (1996).
W-Y Guo et al. Int. J. of Radiation oncology Biol. Phys. (1992).

17. MRI/MRA Follow-up AVM Nidus Evaluation
Nidus obliteration:
Regression to nonvisualization of flow-voids on T2- weighted image and vascular enhancement on enhanced T1-weighted images.
Citation:
MRI was requested for follow up at a 6-month interval for two years after radiosurgery, then yearly until the nidus was shown to be obliterated. Only a few patients underwent MR angiography protocol. (Three dimensional time-of-flight of phase contrast) for a meaningful analysis of this technique to be performed. B.E. Pollock et al. J. Neurosurg. Vol 85 pp , 1996
Findings/Discussion:Magnetic resonance imaging and MRA successfully evaluate the postradiosurgical angioarchitecture of AVM and the surrounding brain parenchyma, providing additional information that reaches outside the scope of conventional angiography. Nidus obliteration was defined on MR by regression to nonvisualization of flow-voids on T2-weighted image and vascular enhancement on enhanced T1-weighted images. Nidus obliteration typically occurs years after radiosurgery. Therefore, angiogram is reserved to confirm/deny obliteration after this period. The parenchymal FLAIR hyperintensity, enhancement and/or mass effect reflect radiation sequela and alteration of local perfusion from post-treatment hemodynamic change. These imaging findings often are present in patients without clinical deterioration. Routine MRI/MRA follow-up is appropriate and conventional angiogram is indicated if there is acute hemorrhage and may be indicated in the setting of neurological decline.
B.E. Pollock et al. J. Neurosurg (1996).

18. Left hemisphere AVM SM Grade 5
Fig. 9: Frontal and lateral left carotid angiography demonstrate a 5 cm AVM nidus (circle) in the left hemisphere with superficial and deep drainage to superior sagittal sinus (arrow) and cerebral Vein of Galen (double arrows).
Fig. 10: Axial MRA Time of flight and T2 MRI demonstrate the AVM nidus (circle) in the eloquent left hemisphere involving language area frontotemporal lobes, insula, and internal capsule and with large flow voids seen in the T2 weighted MRI.
M. Easterling Sayed on right anterior oblique conventional craniocervical arteriography/angiography (pregamma knife) dated 2/8/2013, demonstrates a multifocal arteriovenous malformation with nidus centered about the left frontal and temporal lobes, particularly in the insula. The superior portion of the nidus nidus measures approximately 4.0 x 3.0 x 5.0 cm. The inferior portion of the nidus measures approximately 4.5 x 0.7 x 4.0 cm.. There is enlargement of the left M1 segment and particularly the superior division of the left middle cerebral artery along with multiple left insular branches which supply the arteriovenous malformation. There are multiple and passage vessels. There is also prominent enlargement of the lateral lacunar striate vessels. There appears to be enlargement of the anterior choroidal artery which also appears to supply the inferior portion of the nidus with this smaller branches arising from the left middle cerebral artery and from the left posterior indicating artery are also likely supplying the inferior portion of the nidus. Drainage and is into multiple markedly enlarged venous varices which displaced the left medial cerebral artery branches. There is both superficial and deep deep venous drainage with drainage into the basal vein of Rosenthal and left internal cerebral vein. There is a suggestion of narrowing of the junction of the vein of Galen and the straight sinus. There are multiple dilated cortical veins suggesting venous hypertension.

19. Post Gamma Knife MRA Follow-up Nidus Obliteration by MRA
Fig. 11: Pre Gamma Knife
Axial T2 and Coronal T1 Weighted MR images demonstrate the 5.0 cm left insular and frontotemporal AVM.
Fig. 12: Post Gamma Knife
Coronal and Sagittal 3-D Time of Flight MRA images reveal no flow within the previously described nidus.
Axial T2-weighted FLAIR and coronal T1-weighted postcontrast images dated 6/22/2013 status post, knife radiosurgery demonstrate a large AVM in the left insula within it is measuring approximately 5.0 x 2.5 cm, presumably measuring 5.0 x 3.0 cm. MRA of the circle of Willis using sagittal and coronal 3-D time-of-flight images, there is no evidence of acute ischemia or intraparenchymal hemorrhage.

20. Pre Vs Post Gamma Knife Radiosurgery
Pre Gamma Knife
AVM nidus in left sylvian fissure temporal frontal parietal lobe
Post Gamma Knife
Surrounding vasogenic edema and mass effect
Nidus regression
Fig. 13: Axial T2 FLAIR and T1 Postcontrast
Axial FLAIR, axial T1 precontrast
Size: Greater than 4 cm
Location: None eloquent areas.
Venous drainage: Superficial.
S-M grade: 3-4
IMPRESSION: Left-sided temporal parietal lobe AVM supplied by left middle cerebral artery branches with superficial and deep venous drainage.
4-5 mm right ICA bifurcation aneurysm.
3-4 mm before meals ON aneurysm with hypoplastic left A1 segment of the anterior cerebral artery.
On preoperative MRA dated 5/1/2009: Redemonstrated 3.3 x 1.6 x 2.0 cm irregular tangle of vessels representing an AVM nidus centered about the left sylvian fissure involving the left temporal frontal and parietal lobes. It is supplied by an enlarged left middle cerebral artery. Drainage appear to be both deep and superficial into a markedly enlarged basal vein of Rosenthal as well as thin to multiple large cortical veins. It appears to be large venous varix measuring approximately 1.4 cm in the left sylvian fissure. No definite progression of hemorrhage.
Redemonstration of a 4 mm aneurysm in the right internal cerebral artery bifurcation projecting posteriorly, and a 2-3 mm aneurysm in the anterior communicating artery complex at the junction of the right A1 and A2 segments, projecting inferiorly also not significantly changed when compared to previous
Brain MRI dated 8/3/2010:
Redemonstrated is a triangle of flow void centered within the left perisylvian frontal lobe compatible with patient's known intracranial AVM. The nidus is not as clearly demonstrated as when compared to the prior examination dated 4/5/2008 now with significant development of surrounding FLAIR hyperintensities within the white matter extending focally into the overlying cortical gray matter.
Phase contrast MRV demonstrates a cluster of irregular vein centered at the region of the left frontal and the venous malformation. The venous drainage from this nidus appears isolated to the superficial venous system. No definite the venous drainage is identified. Although angiography has higher sensitivity for evaluation of the venous structures.
IMPRESSION: Left frontal arterial venous malformation appears smaller in size with decreased arterial and venous flow when compared to the prior examination. No definite deep venous drainage is identified. Cerebral edema surrounds the left frontal AVM centered within the adjacent white matter with some focal extension to the overlying gray matter cortex.
2 mm left to right midline shift.
Stable 4 mm right internal carotid artery aneurysm
Fig. 14: Axial T2 FLAIR and T2

21. AVM Gamma Knife Complication Risks
The probability of developing postradiosurgery changes depends mostly on marginal dose (Gy) and treatment volume.
The location of the lesion does not seem to affect the risk of developing imaging changes/complications, but has a marked effect on whether or not these changes are associated with symptoms.
Niranjan. Prog Neurol Surg (2013) .

22. Post Gamma Knife for AVM Radiation Sequela
Radiation-induced T2 hyperintensity:
Transient or permanent signal change in about 29% patients, 2.7% permanent, 9.4% symptomatic
Predictors: prior hemorrhage, large nidus, >24 Gy
Radiation sequela and alteration of local perfusion from post-treatment hemodynamic change
T2 signal. Enhancement and/or mass effect
These imaging findings are not uncommonly seen in patients without clinical problem.
Post gamma complication/outcome based on JNS 2015 Stereotactic radiosurgery for cerebral arteriovenous malformations: evaluation of long-term outcomes in a multicenter cohort Robert M. Stark
Stark. J Neurosurg (2016)

23. Post Gamma Knife MRI Follow-up Radiation Change
Before Gamma Knife
12-month Follow up
24-month Follow up
Figs. 15: Axial FLAIR images show postradiation change with surrounding high T2 signal (arrow) at 12 month and eventual nidus obliteration and near complete resolution of local T2 prolongation on 24-month Follow Up.

24. Left cerebellar AVM SM Grade 2
Fig. 16: Axial T2 and T2 GRE demonstrate flow voids of AVM in left cerebellum
Fig. 17: Frontal and lateral left vertebral artery angioraphies reveal 3 cm left cerebellar AVM supplied by the left PICA (arrow) and PCA (arrowhead), venous drainage into the torcula and transverse sinus (double arrows)

25. Left cerebellar AVM SM Grade 2
Fig. 18: 6 month follow up: Axial T2 FLAIR and Coronal T1 reveal nidus regresson with residual T2 flow void (arrows) and T1 enhancing treated nidus.
M. Finley (pre-gamma knife radiosurgery) dated 3/26/2010, conventional cerebral/cerebellar angiography reveals an approximately 2.8 x 2.7 x 2.2 cm left cerebellar hemisphere arteriovenous malformation which is supplied by the branches of the left superior cerebellar artery, left PICA and possibly the left PICA. The lesion contains intranidal aneurysms and drains into the torcula. Findings during the conventional angiography technique reveal, or are suggestive of intracranial, cerebellar venous hypertension.
Axial T2 FLAIR and coronal T1-weighted postcontrast images(Dated 2/21/2011) reveal interval reduction in size of the left cerebellar venous malformation a decrease around enlarged feeding and draining vessels with 2.5 cm residual enhancing treated nidus. The prominent cerebellar the laryngeal vessels enhancement remains, which was treated on prior angiogram as delayed drainage of venous hypertension. Interval increase in perinatal vasogenic edema without evidence of parenchymal hemorrhage, reflecting treatment change/radiation necrosis and possibly venous congestion.
No evidence of acute ischemia, or evidence of acute/recent intracranial hemorrhage.

26. Post Gamma Knife MRI Follow-up Nidus Regression & Postradiation Change
Fig. 18: 6 month follow up: Axial T2 FLAIR and Coronal T1 post C+ show T2 hyperintensity post radiation change and enhancement of the treated nidus
Fig. 19: 2 year follow up: Axial T2 FLAIR and Coronal T1 Post C+ reveal further nidus regression to obliteration with loss of flow voids and decreased T1 post contrast gliosis (arrows).
T2-weighted FLAIR and coronal T1-weighted postcontrast images dated 3/11/2013 reveal further decrease in the previously described left superior cerebellar arteriovenous malformation now measuring approximately 2.0 x 1.5 x 1.3 cm, previously 2.4 x 1.4 x 1.7 cm. There is no evidence of restricted diffusion (not shown) and there is no evidence of acute, recent cerebral infarctions or intraparenchymal hemorrhages. The ventricular size is now normal. T2-weighted FLAIR images reveal increased surrounding signal intensity in the left posterior fossa. Flow voids within the major cerebral and cerebellar vessels are preserved.
3/26/2010-3/11/2013

27. Post Gamma Knife for AVM Hemorrhage Complications
Annual risk of 1.1% during the latency period
Patients with a history of hemorrhage were more likely to have post-gamma-knife hemorrhage
No hemorrhages in patients with angiographic confirmation of obliteration.
Post gamma complication/outcome based on JNS 2015 Stereotactic radiosurgery for cerebral arteriovenous malformations: evaluation of long-term outcomes in a multicenter cohort Robert M. Stark
Stark. J Neurosurg (2016)

28. Right temporal AVM SM grade 3
Fig. 20: Frontal view left vertebral artery angiography reveals a <3 cm S-M Grade 3 right medial temporal AVM (circle) supplied by the right PCA and draining into the basal vein of Rosenthal (Deep venous drainage).
Fig. 21: Gamma Knife Planning MRI: Axial 3-D CISS and 3-D T1 Gd images reveal a cluster of flow voids nidus in the Right medial temporal lobe (circle).

29. 12-Month Follow Up MRI Hemmorrage
- 12 months after radiosurgery the patient presents with an episode of syncope.
Fig. 22: 12- Month Follow up Axial T2 and FLAIR MRIs performed after GK radiosurgery reveal a intraparenchymal haemorrhage (arrow) in the previously treated AVM with moderate surrounding vasogenic edema (circle).

30. Post Gamma Knife Complication Hemmorrhage
6 Months Post GK
The patient returns to the clinic with increasing headaches.
Fig. 23: Same date visit follow up MRI MRA:
Axial T2 and T2 FLAIR and Coronal and Sagittal 3D Time of Flight MRA reveal interval appearance of a small left intraparenchymal haemorrage (arrows) and mild surrounding edema (arrowhead)
MRA of the circle of Willis performed using Coronal and sagittal views3-D time-of-flight imaging, Status post gamma knife radiosurgery Dated 2/26/2014 which demonstrate a interval appearance of a large left frontotemporal intraparenchymal hemorrhage measuring approximately 1.2 x 0.4 cm. There is early venous filling of some residual superficial deep veins noted indicating AV shunting.. Compared to 6/22/2013 there is interval decrease in the previously described AVM with residual AV shunting. Interval development of signal abnormality surrounding the AVM, most likely post radiosurgical sequela with superimposed posthemorrhagic changes.

31. Post Gamma Knife Complication Resolution of Hemmorrhage & Edema
The patient recovered from headache with supportive care. Fig. 23 MRI Post GK Follow up at 6- months. Fig. 24: MRI Follow up at 12-month Axial T2-weighted FLAIR and coronal T1-weighted postcontrast images reveal decrease edema and hemorrhage with residual gliosis and old blood product. Obliteration of nidus.
Axial T2-weighted FLAIR and coronal T1-weighted postcontrast images dated 5/29/2015 reveal interval moderate decrease in hemorrhage associated with left frontal parietal AVM with marked decrease in surrounding signal abnormality. There is stable size and appearance of a small residual AVM in the anterior aspect of the previously treated left frontal temporal AVM. However, compared to the prior MRI. Adjacent enhancement has substantially decreased. Increased ex vacuo ventricular dilation of the left lateral ventricle are consistent with changes related to evolving hemorrhage.
Anteroposterior view of a conventional cervicocranial left common carotid angiography dated 10/27/2015 compared to a coronal T1-weighted postcontrast MRI in which both demonstrate a residual arteriovenous malformation with AVN nidus located in the left frontal parietal region, Conventional angiography demonstrates no identifiable nidus. Overall stable appearance since the previous brain MRI dated 5/29/2015 and without evidence of acute Intraparenchymal hemorrhage.

32. Follow-up Angiography Confirmation of nidus obliteration
Fig. 25: 12- Month Follow Up Frontal and Lateral Left Common Carotid Craniocervical Angiography after the previous hemorrage displays nidus obliteration and no evidence of contrast extravasation or “Blush”.

33. Summary / Conclusion
Routine brain MRI-MRA represents an acceptable imaging modality to follow AVM patients after radiosurgery.
It is a widely available, noninvasive modality to assess the AVM nidus and post therapeutic appearance and/or complications.
Summary/Conclusion: Routine brain MRI-MRA represents an acceptable imaging modality to follow AVM patients after radiosurgery. It is a widely available, noninvasive modality to assess the nidus and post-therapeutic complications.

34. References:
Starke RM, Kano H, et al. Stereotactic Radiosurgery for cerebral arteriovenous malformations: Evaluation of long term outcomes in a multicenter cohort. J Neurosurg Mar 4:1-9
Barr JC. Ogilyy CS. et al. Selection of treatment modalities or observation of arteriovenous malformation. Neurosurg Clin N Am Jan;23(1):63-75.
Niranjan A, Lunsford LD. et al. Stereotactic Radiosurgery Guideline for the Management of Patients with Intracranial Arteriovenous Malformations. Prog Neurol Surg. Basel, Karger, 2013
Geibprasert, S, Pongpech S, et al. Radiologic Assessment of brain arteriovenous malformations: What the clinician needs to know. Radiographics 2010, 30:
Guo WY, Lindquist C, et al. Gamma Knife Surgeryof cerebral Arteriovenous Malformations: Serial MR imaging studies after radiosurgery. Int. J. Radiation Oncology Biol Phys. 1992, 25:
Hamm KD, Klisch J, et al. Special Aspects of Diagnostic Imaging for Radiosurgery of Arteriovenous Malformations. Neurosurgery : A44-A52
Lang SS, Beslow LA, et al. Follow-Up Imaging to detect Recurrence of Surgically Treated Pediatric Arteriovenous Malformations. J Neurosurg Pediar. 2012, 9(5):
Pollock BE, Kondziolka, D, et al. Magnetic Resonance Imaging: an accurate method to evaluate Arteriovenous Malformations after stereotactic Surgery. J. Neurosurg. 1996, 85: