A comparison of cervical histopathology variability using whole slide digitized images versus glass slides: Experience with a statewide registry

Whole slide imaging is increasingly used for primary and consultative diagnoses, teaching, telepathology, slide sharing, and archiving. We compared pathologist evaluations of glass slides and corresponding digitized images within the context of a statewide surveillance effort. Cervical specimens collected by the New Mexico HPV Pap Registry research program targeted cases diagnosed between 2006 and 2010. Two samples of 250 slides each were digitized with the ScanScope XT (Aperio, Vista, CA) microscope and reviewed with Aperio ImageScope reader. (1) A "random set" had a distribution of community diagnoses: 70% from cases of cervical intraepithelial neoplasia grade 2 or higher, 20% from cases of cervical intraepithelial neoplasia grade 1 and 10% from negative cases. (2) A "discrepant set" was represented by difficult cases where 2 study pathologists initially disagreed. Within the regular workflow of the New Mexico HPV Pap Registry, 3 pathologists read the slides 2 to 3 times each without knowledge of clinical history, previous readings or sampling scheme. Pathologists also read each corresponding image twice. For within- and between-reader comparisons we calculated unweighted κ statistics and asymmetry χ² tests. Across all comparisons, slides and images yielded similar results. For the random set, almost all within-reader and between-reader Kappa values ranged between 0.7 and 0.8 and 0.6 and 0.7, respectively. For the discrepant set, most within- and between-reader κ values were 0.4 to 0.6. As cervical intraepithelial neoplasia diagnostic terminology changes, pathologists may need to re-read histopathology slides to compare disease trends over time, eg, before/after introduction of human papillomavirus vaccination. Diagnosis of cervical intraepithelial neoplasia differed little between slides and corresponding digitized images.