Comparing Whole Slide Imaging and Light Microscopy to Identify Tumor in en face Frozen Sections

To assess accuracy of whole slide imaging (WSI) in the interpretation of permanent and frozen sections in surgical pathology and the identification of tumors in cutaneous en face frozen sections.

Twenty glass slides containing cutaneous en face frozen sections were selected from twenty cases of keratinocyte carcinomas treated with Mohs micrographic surgery. Ten slides contained tumor and ten did not. A blinded dermatologic surgeon used traditional light microscopy (LM) to assess physical slides for tumor presence and type, while noting the confidence (scale 1-10) and time (min) in making the determination. After a seven-day washout period, the surgeon repeated this process using WSI of the same slides, each de-identified and scanned at 20x using the Aperio AT2 (Leica Biosystems).

Percent agreement between LM and WSI was 100%, with Cohen's kappa of 1.0. The average time taken to determine tumor presence was significantly greater using WSI than LM. Similarly, the surgeon was significantly more confident using LM than WSI.

This proof-of-concept study suggests that diagnostic concordance is excellent between LM and WSI in the evaluation of Mohs frozen sections. However, WSI was cumbersome to use, not ergonomic, and required significantly more time.