Arteriovenous Malformation Scores

Table.  Predictive grading systems for procedural risk in the endovascular treatment of brain AVMs.Capture


Buffalo score best predicts procedural risks, although predictive value is modest (AUC ~0.7).



Pulli, B., Stapleton, C., Walcott, B., Koch, M., Raymond, S., & Leslie-Mazwi, T. et al. (2019). Comparison of predictive grading systems for procedural risk in endovascular treatment of brain arteriovenous malformations: analysis of 104 consecutive patients. Journal Of Neurosurgery, 1-9. doi: 10.3171/2019.4.jns19266


The Buffalo Score (AVM)

The Buffalo Score is a new grading system for the endovascular treatment of cerebral AVMs.  It is a 5-point system, and higher scores is associated with higher complication rates.  This new score was created because components of the Spetzler Martin Grading scale, while useful for determining suitability of surgical treatment of cerebral AVMs, may not be relevant in determining suitability for endovascular treatment.

For example, the diameter and number of arterial pedicles supplying the AVM nidus is an important factors to consider in endovascular intervention, since smaller vessels are more prone to injury with catheterization, and a greater number of arterial pedicles produces more risk with each embolization.  The actual size of the AVM nidus and venous drainage pattern is important when considering surgical resection, but is less important during endovascular embolization.

Points for Buffalo Score:

  • number of arterial pedicles
    • 1 point for 1–2 pedicles
    • 2 points for 3–4
    • 3 points greater than 5
  • arterial pedicle diameter
    • 1 point for less than 1 mm
    • 0 points for more than 1 mm
  • eloquence of the location
    • 1 point for eloquent location
    • 0 point for non-eloquent location




Buffalo System Vs. Spetzler Martin Grading System:


*arterial pedicles for Buffalo and draining veins for Spetzler Martin (black lines); nidus (black shading);  deep drainage (dashed lines)

  • Buffalo system = # arterial pedicles (N), diameter of pedicles (D), and eloquence (E)
  • Spetzler–Martin system = venous drainage (V), size (S), eloquence (E)



  1. Measurement of arterial pedicle diameter is made at a distal segment of the arterial pedicle, within 1 cm of the AVM nidus.
  2. Eloquent location is determined based on the nidus location and is defined according to the grading system of Spetzler-Martin.
  3. Any portion of AVM nidus located within motor or sensory cortex, language and vision, and deep eloquent areas (hypothalamus, thalamus, brainstem, cerebellar peduncles) is considered eloquent in location.
  4. This system has not been applied or validated yet.



Levy, EladI et al. “A Proposed Grading System For Endovascular Treatment Of Cerebral Arteriovenous Malformations: Buffalo Score”. Surgical Neurology International 6.1 (2015): 3.


Aneurysms in Arteriovenous Malformations


This figure illustrates the types of aneurysms that are associated with a brain AVM

  • A. distal flow-related aneurysm
  • B. distal flow-related aneurysm
  • C. nidal aneurysm
  • D. proximal flow-related aneurysm
  • E. non-flow-related aneurysm



  • Aneurysms – saccular luminal dilatations of the parent feeding vessel
  • Flow-related aneurysm – an aneurysm that lies on a pathway of an artery supplying the AVM
  • Nidal aneurysm – aneurysm that is contiguous with the vascular mass include in the AVM size measurement
  • Proximal aneurysms – located on the vessel or branch points of the circle of Willis or proximal to it (i.e. ICA, ACA, PPCA, A1 or P1, VA or BA)
  • Distal aneurysms – more distal locations beyond the circle of Willis.



“Reporting Terminology For Brain Arteriovenous Malformation Clinical And Radiographic Features For Use In Clinical Trials”. Stroke 32.6 (2001): 1430-1442. Web.

Determining AVM Size

Size of brain AVMs is measured on the pre-treatment MRI in the 3 views which includes the AVM’s largest diameter.



Measure AVM size in 3 dimensions from pretreatment angiogram in lateral and anteroposterior projections (see Figure above) or from the MRI axial cuts.  From these dimensions, a calculation can be made to estimate AVM volume in mL with the ABC/2 formula.


“Reporting Terminology For Brain Arteriovenous Malformation Clinical And Radiographic Features For Use In Clinical Trials”. Stroke 32.6 (2001): 1430-1442. Web.

Spetzler and Martin Grading for AVM



AVM Grading System

Spetzler-Martin grading system

  • stratify morbidity risk in patients following complete microsurgical resection of brain AVM to help inform treatment decision
  • AVM size (largest diameter of nidus)
    • < 3 cm = 1 point
    • 3-6 cm = 2 points
    • > 6 cm = 3 points
  • deep venous drainage = 1 point
    • deep veins include internal cerebral veins, basal veins, precentral cerebellar vein
    • all veins in posterior fossa are deep except for cerebellar hemispheric veins that drain into straight sinus transverse sinus
  • AVM adjacent to eloquent brain areas = 1 point
    • eloquent indicates identifiable neurological function and disabling neurological deficit if injured
    • includes sensorimotor, language, and visual cortices; hypothalamus and thalamus; internal capsule, brainstem, cerebellar peduncles, and deep cerebellar nuclei
  • grade = sum of scores (total score range 1-5 points)
  • major postsurgery deficits (0% mortality)
    • hemiparesis
    • long-term increase in aphasia
    • homonymous hemianopsia
    • severe deficit (including presumed normal perfusion pressure breakthrough) with major aphasia and hemiparesis

Postsurgery Outcomes Stratified by SM Grade:


AVM Validation

AVM Notes AVM Eloquent AVM morbidity  AVM factors AVM 08 AVM 01 AVM 02 AVM 03 AVM 04 AVM 05 AVM 06 AVM 07



Postsurgery Outcomes Stratified by SM Grade:




Spetzler, Robert F., and Neil A. Martin. “A Proposed Grading System For Arteriovenous Malformations”. Journal of Neurosurgery 65.4 (1986): 476-483. Web.