An algorithm for preoperative differential diagnostics of parotid tumours on the basis of their dynamic and diffusion-weighted magnetic resonance images: a retrospective analysis of 158 cases

Background: To verify the usefulness of a new algorithm for preoperative differential diagnostics of parotid tumours on the basis of their dynamic and diffusion- -weighted magnetic resonance imaging (MRI). Materials and methods: The retrospective analysis included 158 consecutive surgical patients with parotid tumours. Aside from ultrasound-guided fine needle biopsy, the protocol of preoperative evaluation included dynamic and diffusion-weighted MRI. According to the new diagnostic algorithm, the result of fine needle biopsy was considered only in the case of lesions with time to peak enhancement (Tpeak) > 60 s and washout rate (WR) ≤ 30% on dynamic MRI and apparent diffusion coefficient (ADC) ≤ 1.7 × 103 mm/s2 on diffusion-weighted MRI, or those presenting with concomitant lymphadenopathy. The accuracy of this algorithm was verified against final histopathological diagnoses. Results: The new algorithm gave 10 true positive and 2 false positive results, as well as 132 and 14 true and false negative results, respectively. Its sensitivity and specificity (41.7% and 98.5%, respectively) were the same as in the case of fine needle biopsy alone. None of the 59 tumours that were qualified as benign solely on the basis of preoperative MRI turned out to be malignant on postoperative histopathological examination. Conclusions: Interpreted together, dynamic and diffusion-weighted MRIs provide the same accuracy in preoperative differential diagnostics of parotid tumours as fine needle biopsy. This substantiates the use of diagnostic algorithms in which biopsy would serve mostly as a secondary test to verify selected ambiguous radiological diagnoses. (Folia Morphol 2018; 77, 1: 29–35)