Validation of whole-slide digitally imaged melanocytic lesions: Does z-stack scanning improve diagnostic accuracy?
Bart Sturm1, David Creytens2, Martin G Cook3, Jan Smits4, Marcory C. R. F. van Dijk5, Erik Eijken6, Eline Kurpershoek4, Heidi V. N Küsters-Vandevelde7, Ariadne H. A. G. Ooms4, Carla Wauters7, Willeke A. M. Blokx8, Jeroen A. W. M. van der Laak1
1 Department of Pathology, Radboud University Medical Center, Nijmegen, The Netherlands
2 Department of Pathology, Ghent University Hospital, Ghent, Belgium
3 Department of Histopathology, Royal Surrey County Hospital, Guildford, United Kingdom
4 Pathan B.V., Rotterdam, The Netherlands
5 Pathology-DNA, Rijnstate Hospital, Arnhem, The Netherlands
6 Laboratory for Pathology East Netherlands (LabPON), Hengelo, The Netherlands
7 Department of Pathology, Canisius Wilhelmina Hospital, Nijmegen, The Netherlands
8 Department of Pathology, University Medical Center Utrecht, Utrecht, The Netherlands
Jeroen A. W. M. van der Laak
Department of Pathology, Radboud University Medical Center, 824, P.O. Box 9101, 6500HB, Nijmegen
Source of Support: None, Conflict of Interest: None
Background: Accurate diagnosis of melanocytic lesions is challenging, even for expert pathologists. Nowadays, whole-slide imaging (WSI) is used for routine clinical pathology diagnosis in several laboratories. One of the limitations of WSI, as it is most often used, is the lack of a multiplanar focusing option. In this study, we aim to establish the diagnostic accuracy of WSI for melanocytic lesions and investigate the potential accuracy increase of z-stack scanning. Z-stack enables pathologists to use a software focus adjustment, comparable to the fine-focus knob of a conventional light microscope. Materials and Methods: Melanocytic lesions (n = 102) were selected from our pathology archives: 35 nevi, 5 spitzoid tumors of unknown malignant potential, and 62 malignant melanomas, including 10 nevoid melanomas. All slides were scanned at a magnification comparable to use of a ×40 objective, in z-stack mode. A ground truth diagnosis was established on the glass slides by four academic dermatopathologists with a special interest in the diagnosis of melanoma. Six nonacademic surgical pathologists subspecialized in dermatopathology examined the cases by WSI. Results: An expert consensus diagnosis was achieved in 99 (97%) of cases. Concordance rates between surgical pathologists and the ground truth varied between 75% and 90%, excluding nevoid melanoma cases. Concordance rates of nevoid melanoma varied between 10% and 80%. Pathologists used the software focusing option in 7%–28% of cases, which in 1 case of nevoid melanoma resulted in correcting a misdiagnosis after finding a dermal mitosis. Conclusion: Diagnostic accuracy of melanocytic lesions based on glass slides and WSI is comparable with previous publications. A large variability in diagnostic accuracy of nevoid melanoma does exist. Our results show that z-stack scanning, in general, does not increase the diagnostic accuracy of melanocytic.