Frozen Section of Parotid Gland Tumours: The Head and Neck Pathologist as a Key Member of the Surgical Team

Abstract

Introduction: The aim of this study was to evaluate the impact of subspecialised head and neck versus general surgical pathologists on the reliability of the histopathologic evaluation during intraoperative consultation. Materials and Methods: The medical records of all patients who underwent a parotidectomy with frozen section between 2006 and 2021 were retrospectively evaluated. The frozen section was evaluated for sensitivity, specificity, accuracy, and predictive value. Assessment by two groups of pathologists (subspecialised head and neck versus general surgical pathologists) was compared, and the nature or types of misdiagnoses compared with final diagnoses on paraffin sections were analysed for the two groups. Results: Our study sample was made up of 669 cases. The mean age of patients was 57.7 years (range: 10−94 years). Of these, 490 patients had a benign lesion (73.2%), whereas 179 patients had a malignant lesion (26.8%). Frozen section had an overall accuracy of 97.6%, sensitivity for malignancy was 91.1%, specificity was 100%, PPV was 100%, and the NPV was 96.8%. The exact histologic subtype in the group of malignant tumours was correctly identified in FS in 89.4% of cases. A comparison of head and neck pathologists versus general surgical pathologists revealed a highly statistically significant difference concerning both overall detection of malignancy (p < 0.001) as well as correct identification of the histologic subtype (p < 0.001). Conclusion: Involvement of subspecialised head and neck pathologists in the intraoperative consultation for salivary gland tumours results in a gain of 19.8% more sensitivity, underlining the importance of specialisation in salivary gland pathology for the optimisation of frozen section quality.

Keywords: accuracy; benign tumour; frozen section; head and neck cancer; malignant tumour; parotid gland; predictive value; sensitivity; specificity.

Figure 1

Performance of frozen section by a subspecialised head and neck pathologist, and performance of frozen section concerning correct identification of malignant tumours and their histologic subtypes over the years (the number of examined cases per year is given next to each year in the x axis of the diagram).

Figure 2

(A) (frozen section) and (B) (permanent section) of epithelial-myoepithelial carcinoma. This rare entity is essentially not reliably distinguishable from pleomorphic adenoma with diffuse ductal component interrupted by myoepithelial cells (interpretative error). This applies frequently to both general surgical pathologists and head and neck pathologists. (C) (frozen section) and (D) (permanent section) of adenoid cystic carcinoma with predominantly encapsulated pattern (stars). This interpretative error is frequently seen in cases seen by general surgical pathologists but not by head and neck pathologists. A focal invasive component (red arrows) was also present in the frozen section (interpretative error). (E) (frozen section) and (F) (permanent section) of cystic and oncocytic mucoepidermoid carcinoma misinterpreted as cystadenolymphoma (“Warthin’s tumor”) by the general surgical pathologist, despite absence of lymphoid tissue and bilayered oncocytes and presence of multifocal mucus cells (interpretative error). Small image: overview showing solid and cystic lesion.