[Accuracy of frozen section diagnosis: an analysis of 1695 consecutive cases].

BACKGROUND: The intraoperative frozen section is a well established procedure for rapid diagnosis that helps in making therapeutic decisions. AIM: Assessment of the accuracy of frozen section diagnosis and analysis of the causes of its discordance. METHODS: A retrospective review of 1695 surgical specimens performed in 1207 patients between January 2002 and April 2005. Frozen section results were compared with the final diagnoses in paraffin sections. RESULTS: The frozen section diagnosis was benign in 84.2%, malignant in 10.2% and borderline in 0.4% of all cases. The frozen section result was deffered to permanent section in 5.2%. The sensitivity, specificity, positive and negative predictive values were 84.6%, 99.8%, 98.2% and 97.8% respectively. Overall diagnostic agreement was 97.5% (Kappa=0.88). Frozen section diagnosis was incorrect in 2.5% of cases. Most of the discrepancies were false negative cases frequently due to sampling errors and misinterpretation. False positive cases were always related with misinterpretation. CONCLUSION: The frozen section evaluation is highly accurate and reliable. However, the surgeon and the pathologist must be aware of its limitations.