Sensitivity of Fine-Needle Aspiration and Imaging Modalities in the Diagnosis of Low-Grade Mucoepidermoid Carcinoma of the Parotid Gland

Objective: To determine the diagnostic accuracy of fine-needle aspiration (FNA) and imaging modalities for low-grade mucoepidermoid carcinoma (MEC) of the parotid gland. Methods: Retrospective chart review of patients diagnosed with low-grade MEC of the parotid gland following surgical excision between January 2010 and June 2018. Imaging from patients with MEC were randomly mixed with imaging from patients with benign pathology and reviewed in a blinded fashion. Main outcome measure was sensitivity. Results: A total of 24 patients were confirmed to have had low-grade MEC on final pathology, with a total of 31 FNAs performed between them. Twelve of 31 FNAs were positive for low-grade MEC, with a sensitivity of 39%. A total of 27 imaging studies were reviewed, which included 16 patients with low-grade MEC and 11 patients with benign pathology. Of these 27 imaging studies, 10 were declared indeterminate. Of the remaining 17 imaging studies, 13 were reviewed as malignant (11 true positive and 2 false positive) and 4 as benign (4 true negative). Overall magnetic resonance imaging (MRI) sensitivity for low-grade MEC was 100% (9/9) with 95% CI (0.66-1.0) when considering indeterminate results as positive for malignancy. Conclusion: This study reaffirms that for low-grade MEC, sensitivity of FNA is poor. MRI provides an important diagnostic tool in the evaluation of salivary gland neoplasms, due to its increased sensitivity for low-grade MEC when considering indeterminate results as positive. This provides confidence in the diagnosis of benign tumors and allows appropriate counseling of all options to the patient, including observation. Imaging and low threshold of excision should be considered despite an inflammatory or benign FNA.