Warthin's tumor in the era of hybrid imaging with SPECT-CT and PET-CT: Features, indications and value of different functional and anatomical modalities

Learning Objectives 1. Evaluation of Warthin's tumors. 2. An FDG avid parotid lesion is not always malignant as Warthin's can frequently be FDG avid. 3. Accuracy, simplicity and easy reproducibility of salivary gland scintigraphy. 4. Multimodality imaging with expert opinion can be useful.

Various imaging techniques have been used to guide clinical and surgical management in salivary gland lesions. We propose to review different imaging techniques used in the evaluation of a suspected Warthin’s tumor. Warthin's tumor is the second most common benign parotid tumor. It usually occurs in older patients (6-7th decade of life). It most commonly presents incidentally on CT studies and nowadays on PET scans as well as in the work up of other processes involving the head and neck. This leads to a diagnostic dilemma. Is the parotid mass benign or malignant? Salivary gland imaging with 99mTc-labeled sodium pertechnetate (Na[99mTcO4-]) has been utilized to diagnose Warthin’s tumors with high accuracy: 87% (sensitivity: 78%, a specificity of 91%); in addition, this test is also simple to perform [1}. Other modalities have been used to evaluate salivary gland pathology including 123Iodine, 131Iodine, 67Gallium or 18F-FDG (PET-CT), as well as ultrasound, CT, and MRI. Ultrasound has been described as a modality which can identify a Warthin’s tumor based on echostructure, margins and vascularity. CT utilizes structure, margins, number of lesions, pattern of enhancement, washout time-frames and attenuation coefficients to differentiate between various parotid tumors. The current role of MRI is predominantly in the pre-surgical delineation of facial nerve anatomy. Many investigators have attempted to use quantitative parameters in the evaluation of parotid masses including peak signal intensities, washout patterns, apparent diffusion coefficient (ADC) cutoffs, and lesion-to-muscle magnetization transfer ratios