Until now, many articles have been published to declare that apparent diffusion coeficient calculation (ADC) by diffusion-weighted imaging (DWI) is a helpful method for differantiating malignant from benign parotid gland tumors. Habermann et al. in 2005 described that diffusion-weighted echo-planar MRI seems to be a valuable tool for differentiating benign from malignant primary parotid gland tumors in fifty consecutive patients (1). We read with interest the recent article of the same group in the January 2009 issue of the AJNR (2). The authors reached one different conclusion in one hundred thirty-six patients with parotid tumors. They claimed that, DWI has the potential to differentiate only pleomorphic adenoma and myoepithelial adenomas from other parotid tumor types and state that “…in contrast to most other studies, an overlap regarding the ADC values from Warthin tumors and three different malignant subtypes of parotid gland lesions…” is present.

We would like to draw the authors’ attention to our report that is previously published in 2007 (3). We had already determined that DWI appears to be useful for distinguishing pleomorphic adenomas from other types of parotid gland tumors and calculating ADC values did not help to differentiate Warthin tumors from malignant parotid tumors. We are pleased that the good designed study with large patient population by Habermann and coworkers supports our results.

In our experience, morphologic criteria such as irreguler border, invasion of the mass and heterogeneous hypointense signals on T2-weighted images are still valuable in diagnosing malignant parotid tumors.

References

1. Habermann CR, Gossrau P, Graessner J, et al. Diffusion-weighted echo-planar MRI: a valuable tool for differentiating primary parotid gland tumors? Rofo 2005;177:940-5.
2. Habermann CR, Arndt C, Graessner J. Diffusion-Weighted Echo-Planar MR Imaging of Primary Parotid Gland Tumors: Is a Prediction of Different Histologic Subtypes Possible? AJNR Am J Neuroradiol published 8 January 2009, 10.3174/AJNR.A1412
3. Yerli H, Agildere AM, Aydin E, et al. Value of apparent diffusion coefficient calculation in the differential diagnosis of parotid gland tumors. Acta Radiol 2007; 48: 980-7.