[Role of diffusion weighted MR in the diagnosis of parotid tumours].

To evaluate the contribution of sequences of diffusion for the diagnosis of nature of the tumours of the parotid.Retrospective study based on 29 patients all operated of a parotid tumour They had a MRI in conventional acquisition (T1, T1 Gadolinium, T2) and in sequences of diffusion. An ADC cartography (apparent coefficient of diffusion) and an ADC ratio between the tumoral area and the healthy controlateral parotid were successively analyzed by two experienced radiologists. We calculated the effectiveness of these MRI sequences, focusing more particularly on the diagnosis of the malignant tumours. We also determined the sensitivity and the specificity of the sequences of diffusion, with their positive and negative predictive values.On the 7 malignant tumours, 3 had been classified wrongly like benign thanks to the only cartography of diffusion. We obtained a sensitivity of this examination for the diagnosis of malignity of 57%. Out of the 22 benign tumours, 1 only was classified wrongly like malignant. The specificity of the diffusion for the diagnosis of malignity thus rose with 95%, its positive predictive value with 80% and its negative predictive value to 87%. It should be noted that all the malignant tumours had an ADC ratio lower or equal to 1.8.The histological characteristics of the malignant tumours of the parotid are very variable. Generally, they have large nuclei associated with a hypercellularity involving a decrease of the ADC. The results of this MRI sequence are encouraging even if they remain not very reliable in front of cystic or necrotic tumours.