Imaging biomarkers in the diagnosis of salivary gland tumors: the value of lesion/parenchyma ratio of perfusion-MR pharmacokinetic parameters

Morphologic magnetic resonance imaging (MRI) for characterization of salivary gland tumors has limited utility, and the use of perfusion MRI data in the clinical setting is controversial. We examined the potential of tissue-normalized dynamic contrast-enhanced (DCE) MRI pharmacokinetic parameters of salivary gland tumors as imaging biomarkers for characterization and differentiation between benign and malignant lesions. DCE-MR images acquired from 60 patients with parotid and submandibular gland tumors were retrospectively reviewed. Pharmacokinetic parameters as transfer constant (Ktrans), rate constant (Kep), extracellular space volume (Ve), fractional plasma volume (Vp), and AEC (area of all times enhancement curve) were measured on both the lesion and the normal contralateral salivary gland parenchyma. Lesion/parenchyma ratio (L/P) for each parameter was calculated. Five groups of lesions were identified (reference: histopathology): pleomorphic adenomas(n = 20), Warthin tumors(n = 16), other benign entities(n = 4), non-Hodgkin lymphomas(n = 4), and malignancies(n = 16). Significant differences were seen for mean values of L/PKtrans (higher in malignancies), L/PKep (lower in adenomas than Warthin tumors), L/PVe (lower in Warthin tumors and lymphomas), L/PVp (higher in Warthin tumors and malignancies than adenomas), and L/PAEC (higher in malignancies). Significant differences were found between benign and malignant (non-lymphoproliferative) lesions in mean value of L/PKtrans (0.485 and 1.581), L/PVp (1.288 and 2.834), and L/PAEC (0.682 and 1.910). ROC analysis demonstrated the highest AUC (0.96) for L/PAEC, with sensitivity and specificity for malignancy of 93.8% and 97.5% (cutoff value = 1.038). Lesion/parenchyma ratio of DCE-MRI pharmacokinetic data could be helpful for recognizing the principal types of salivary gland tumors; L/PAEC seems a valuable biomarker for differentiating benign from malignant tumors.