Salivary gland lesions: diagnostic reliability and challenges of fine needle aspiration cytology

Abstract

Fine needle aspiration cytology (FNAC) is a valuable, safe and widely used method for preoperative diagnosis of salivary gland lesions. The diagnostic accuracy of FNAC is dependent on the quality and yield of the aspirate, as well as the experience and knowledge of the cytopathologist. 247 cases of FNAC of salivary gland lesions were performed in our 4-year retrospective study. FNAC diagnoses were divided into non-neoplastic lesions, benign and malignant neoplasms. Histopathologic confirmation was done in 101 cases. The cases with discrepancies between the FNAC and histopathologic results were reviewed to establish possible reasons for discordance. The measures of diagnostic validity of FNAC in diagnosing non-neoplastic, benign and malignant lesions were evaluated. Of the 247 FNAC samples, 135 cases were diagnosed as benign neoplasms, 15 as malignant neoplasms, and 97 as non-neoplastic lesions. Out of the 101 cases with histopathologic confirmation, discordant results between cytologic and histopathologic diagnosis were observed in 15 cases. Our study showed no false positive and 4 false negative results for cancer. Cystic presentation of a lesion was a common reason for diagnostic pitfall. Sensitivity of FNAC in various types of salivary gland lesions ranged from 75%-100%, specificity 81-100%, diagnostic accuracy 85-96%, PPV 31-100% and NPV 60-96%. FNAC is a highly sensitive and specific method for diagnosis of most salivary gland lesions. Despite the fact that histopathology remains the gold standard, preoperative FNAC should be considered for preliminary investigation. Due to the diagnostic pitfalls, FNAC should be used in conjunction with clinical information, physical examination, and radiologic findings to reach the right diagnosis.

Keywords: Salivary gland lesions; cytopathology; diagnostic validity; fine needle aspiration cytology; histopathology.

Figure 1

Receiver operator characteristic (ROC) curve analysis: (A) ROC curve with malignancy on surgical follow-up as end point, (B) ROC curve with benign neoplasm on surgical follow-up as the end point, (C) ROC curve with non-neoplastic lesion on surgical follow-up as the end point.

Figure 2

Cytologic (A) and histologic (B) findings of a basal cell adenoma case misdiagnosed as cyst. The FNAC smear (A) shows proteinaceous material with macrophages (H&E, ×400), and histologically (B) a trabecular pattern of growth of basal cell adenoma is observed (H&E, ×100).

Figure 3

Adenoid cystic carcinoma case showing diagnostic discrepancies. A case, diagnosed as basal cell adenoma, shows in FNAC smear (A) nests of cells with hyperchromatic nuclei, no nucleoli, and scant cytoplasm (H&E, ×400). Histopathology (B) reveals tubular and cribriform architecture of adenoid cystic carcinoma with perineural invasion (arrow) (H&E, ×100).

Figure 4

Diagnostic pitfalls in mucoepidermoid carcinoma case which was diagnosed as Warthin tumor by FNAC. Cytologic (A) findings reveal groups of oncocytic cells and crushed lymphoid tangles in the proteinaceous material (H&E, ×200), while histopathology (B) shows occasional oncocytic change and inflammatory reaction in mucoepidermoid carcinoma area (H&E, ×200).

Figure 5

Cytologic (A) and histologic (B) findings of epithelial-myoepithelial carcinoma misdiagnosed as an undetermined benign neoplasm. The cytology smear (A) displays monomorphic epithelial cells without overt cytologic features of malignancy in nests and dispersion and psammoma bodies (H&E, ×200). Histopathology (B) shows islands of epithelial and myoepithelial cells with mild nuclear pleomorphism and numerous psammoma bodies (H&E, ×200).