AVM Morphological Characteristics Protocol

The comprehensive protocol for data quality management is available in eMethods 1 in Supplement 1. Demographic information, including sex, age, and modified Rankin Scale Score (which measures degree of disability or dependence after a stroke) at hospital admission, was recorded. Radiographic variables describing AVM morphological characteristics, including nidus location, size, diffuseness, venous drainage (drainage patterns, stenosis, and venous aneurysms), feeding arteries (number, dilation, multiple sources, and perforating arteries), associated aneurysm, and hemorrhagic presentation, were collected. Radiological information was determined via digital subtraction angiography and MRI.
The nidus location was regarded as deep if the lesion exclusively involved the brain stem, cerebellum, basal ganglia, thalamus, corpus callosum, or insular lobe. The definition of eloquent regions (ie, sensory, motor, language, or visual cortex; hypothalamus or thalamus; internal capsule; brain stem; cerebellar peduncles [superior, middle, or inferior]; and deep cerebellar nuclei) was based on the Spetzler-Martin Grading Scale.^{5 (link)} The size of AVMs was dichotomized into small and large based on whether the maximum nidal diameter was less than 3 cm or 3 cm or greater. Ventricular system involvement was determined via MRI based on whether the nidal border was adjacent to the cerebral ventricular system. Feeding arteries were considered dilated when their diameter was at least twice that of the same blood vessel segments. Venous aneurysm was defined as the focal aneurysmal dilation of the proximal drainage vein.^{18 (link)} Hemorrhagic presentation was defined as hemorrhage that could be ascribed to AVM rupture before or at admission.