Bilateral synchronous and multifocal Warthin's tumor mimicking metastases from lung cancer: A rare cause of false positive flourodeoxy glucose positron emission tomography/computed tomography

Sir,

Several benign and inflammatory etiologies are known to produce false positive results on positron emission tomography/computed tomography (PET/CT) study done using flourine-18-flourodeoxy glucose (F-18 FDG) as tracer. Warthin's tumor (WT) is one such common benign tumor of the salivary gland, which although infrequently can be seen synchronously with other malignancies, can mimic metastasis by virtue of its avid FDG uptake. We report the case of a 43-year-old male smoker, diagnosed with lung cancer who underwent a pre-treatment whole body staging FDG PET/CT study. The maximum intensity projection image [Figure 1] revealed increased tracer uptake in the chest corresponding to the primary tumor in the right lung. In addition, multiple FDG avid foci were seen bilaterally in the neck. Intense FDG uptake was also seen in multiple soft tissue nodules in both the parotid glands. The PET/CT findings [Figure 2] suggested a possibility of parotid metastasis from the primary tumor in the right lung. However, the nodules demonstrated a well-defined outline on CT images, a finding that is frequently seen in benign lesions;[1] also metastases to the parotid from a primary tumor in the lungs are exceedingly rare with only one case reported in a recent study of 178 parotid metastases.[2] This prompted a correlation with an ultrasound-guided cytological examination of the avid parotid nodules that revealed bilateral multifocal WT.

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Figure 1

Flourine-18-flourodeoxy glucose (F-18 FDG) positron emission tomography/computed tomography maximum intensity projection image showing increased tracer uptake in the chest (curved arrow) corresponding to the primary tumor in the right lung. Multiple flourodeoxy glucose avid foci are also seen bilaterally in the neck (arrows)

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Figure 2

Axial positron emission tomography images (b and e) showing intense flourodeoxy glucose uptake (maximum standardized uptake SUV_max 12.8) in the parotid region corresponding to multiple soft tissue nodules in both the parotid glands seen on axial computed tomography (CT) (a and d) and fusion PET/CT images (c and f) (arrows)

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Papillary cystadenoma lymphomatosum or WT is the second most common benign salivary gland tumor, with an incidence peak in the sixth decade, affecting males slighter more than females.[3] Commonly, WT presents unilaterally as a unifocal tumor. Multifocal WT, though seen infrequently, is unilateral in most cases.[45] Also, the occurrence of multifocal disease is generally metachronous.[6] However, a combination of bilateral, synchronous, and multifocal WTs as found in our patient is a rare occurrence.[7] There is limited work on FDG PET in salivary gland tumors, but WT, though of benign nature, has been shown to concentrate FDG avidly, with uptake often falling in the range of its malignant counterparts, thereby lowering the sensitivity of PET in separating benign and malignant salivary tumors.[8] Our case is an extrapolation of the results of the above study,[8] and serves to uncover the confounding effect of variable and often intense FDG uptake in WT on interpretation of PET/CT studies. The rare occurrence of bilateral, synchronous, and multiple WT showing intense FDG uptake can thus be a potential cause of false positive results when PET studies are performed for evaluation of salivary tumors or for metastatic work-up of other malignancies as demonstrated.