Reproducibility analysis of a new objective method for measuring arteriovenous malformation nidus size at angiography

Currently, no specific method exists to measure arteriovenous malformation (AVM) nidus size, a requirement in assessing the success of treatment. Additionally, the commonly used evaluation provides only a linear one-dimensional measurement of this three-dimensional entity. The purpose of this study was to devise an improved method for measuring AVM nidus size, an irregularly shaped radiologic entity, that provides objective and reproducible results.

The procedure involved digitizing angiograms obtained before and after treatment, making the gray scale uniform, printing images on standard bond paper, delineating the nidus area, measuring the nidus area with a polar planimeter, and finally, correcting for geometric magnification. Three observers made the measurements. The corrected nidus areas were tabulated, and the mean, standard deviation, interobserver variability, and confidence intervals (CIs) were calculated.

On both anteroposterior and lateral views, the Kendall coefficient of concordance (a measure of interobserver variability) was equal to 0.97, signifying excellent agreement. Additionally, these values were within the 95% CIs; this result showed that they were unlikely the result of chance.

Precise measurements of an AVM nidus are required to properly analyze changes in the lesion after endovascular embolization (ie, to evaluate treatment success). Because of the irregular contours of an AVM nidus, measuring an area with planimetry, rather than with the usual linear dimensions, should yield more exact results.