Evaluation of frozen section diagnosis in 721 parotid gland lesions

Sir: We compared the diagnosis obtained by frozen section (FS) and the final histological diagnosis (FD) in the largest series of parotid tumours ever assembled (721 cases over 30 years). We will neither debate the usefulness of FS versus or in combination with fineneedle aspiration (FNA), nor discuss how FS diagnosis influences surgical decision making, but we will demonstrate the reliability of FS diagnosis in comparison with FD and point out the difficulties encountered by the pathologist. Diagnosis of the lesions was made according to the World Health Organization classification and they were classified into the following categories: true positive, false positive, true negative and false negative. On FD, 124 patients (17.2%) had a malignant tumour, whereas 597 patients (82.8%) had a benign lesion. Sensitivity and specificity of FS were 74% and 99%, respectively. On FD, 91 cases (93.8%) were truly malignant and six cases revealed false positivity (Table 1). The 97 malignant cases on FS were considered as carcinoma (n 1⁄4 79), lymphoma (n 1⁄4 15) and metastatic melanoma (n 1⁄4 3). Of the 79 lesions diagnosed as carcinoma on FS, 73 were truly malignant and corresponded to carcinoma (n 1⁄4 69), lymphoma (n 1⁄4 1), myogenic sarcoma (n 1⁄4 2) and metastatic melanoma (n 1⁄4 1). On FS, 597 benign lesions were considered to be adenoma (n 1⁄4 481), cyst (n 1⁄4 62), lymph node (n 1⁄4 24), inflammatory lesion (n 1⁄4 11), benign lymphoepithelial lesion (n 1⁄4 9), haemangioma (n 1⁄4 3), haematoma (n 1⁄4 1), lipoma (n 1⁄4 4), leiomyoma (n 1⁄4 1) and schwannoma (n 1⁄4 1). On FD, 573 of these 597 cases (96%) were truly benign lesions, whereas 24 were malignant (false negative) (Table 1). The 481 cases considered to be adenoma on FS examination were further classified intraoperatively as pleomorphic adenoma (n 1⁄4 313), Warthin’s tumour (n 1⁄4 123), basal cell adenoma (n 1⁄4 14) and adenoma not otherwise specified (n 1⁄4 31). The diagnosis of pleomorphic adenoma was established on FD in 292 of 313 cases. The remaining 21 cases were diagnosed as Warthin’s tumour (n 1⁄4 1), adenoma (n 1⁄4 2), basal cell adenoma (n 1⁄4 5), oncocytoma (n 1⁄4 2), adenoid cystic carcinoma (n 1⁄4 2), carcinoma ex mixed tumour (n 1⁄4 5), adenocarcinoma (n 1⁄4 1), mucoepidermoid carcinoma (n 1⁄4 2) and lymphoma (n 1⁄4 1). The diagnosis of Warthin’s tumour was ascertained on FD in 119 of 123 cases. The remaining four lesions were diagnosed as mucinous cystadenoma (n 1⁄4 1), cyst (n 1⁄4 2) and intraductal papilloma (n 1⁄4 1). Results regarding soft tissue, lymphoid tissue and cystic lesions on FS examination are presented in Table 2. Fifteen cases were suspect on FS (Table 3). Twelve cases were inconclusive. Clinical and radiological findings are of great value in defining the location and anatomical extent of a parotid tumour but, in some cases, lack specificity in determining its nature. The preoperative diagnosis of parotid gland lesions is nowadays accomplished with FNA biopsy, which changes the therapeutic approach in up to 35% of cases, allowing the avoidance of surgery in some patients. In fact, FS in parotid gland surgery is useful because it allows for evaluation of the margins, but its accuracy for histological diagnosis is variable and debated in the literature. The sensitivity of FS for the diagnosis of malignancy Table 1. Incorrect frozen section diagnoses