Radiological imaging in primary parotid malignancy

In a retrospective analysis of the preoperative imaging of patients presenting with primary malignant parotid disease, all relevant images were collected and reviewed by two experienced head and neck radiologists, blinded to the diagnosis. Forty-two patients (25 male, 17 female), median age 67.5 years (range 15-86), were included in the study of which 32 had undergone CT scanning, nine MR and three ultrasound. Forty tumours (93%) were correctly diagnosed as malignant when compared with histology. The two false negatives arose in a patient who had received an ultrasound scan only and in a patient with lymphoma, whose CT scan was reported as a pleomorphic adenoma. Neither had undergone prior radiotherapy. A poorly defined tumour boundary was the most consistent observation for both MR and CT images for the malignant tumours examined. Local infiltration was correctly correlated with pathological findings in eight of the nine MR scans, however, CT proved less reliable, correct in 14 of 24 cases (p=0.01). No correlation was identified between any of the imaging features examined and the final histological diagnosis. A poorly defined tumour boundary with evidence of local invasion was the best indicator of malignancy and was reported more frequently from MR scans than from CT. Imaging alone, however, proved unreliable in the prediction of final histological diagnosis or grade of tumour.