Parotid Lesions
The majority of FDG-avid parotid lesions are benign (80%), nearly always representing Warthin’s tumors or pleomorphic adenomas.
There is considerable debate on how to best report the incidental finding of an FDG-avid parotid nodule. Some radiologists simply recommend biopsy in all cases, reflexively reporting that “malignancy cannot be excluded.”
We favor interpretation in the context of the malignancy and the specific presentation of the case at hand (“Oncologic Plausibility”, discussed here).
For example, in a head and neck cancer with multiple hypermetabolic cervical nodes and a hot parotid nodule, we suggest that the parotid lesion may be metastatic:
“While this FDG avid right parotid soft tissue nodule may represent a benign Warthin’s tumor or pleomorphic adenoma, it is moderately suspicious for a metastatic lymph node in this patient with a history of right tonsillar cancer.”
If on the other hand, if it seems more likely to be an incidental finding (e.g. sigmoid cancer primary without evidence of other metastatic disease), we strongly favor a benign parotid lesion:
“While a malignant lesion cannot be entirely excluded, this typically represents either a benign Warthin’s tumor or pleomorphic adenoma.”
Interestingly, as most oncology patients will receive follow up exams after chemotherapy, the true diagnosis of a parotid lesion is often revealed on the subsequent scan:
- If the follow up scan reveals resolution of all hypermetabolic nodes with persistence of an intensely FDG-avid parotid lesion, the lesion is almost invariably a benign parotid neoplasm.
- If the nodes AND the parotid lesion disappear on the follow up exam, we can confidently assume the parotid lesion represented malignancy.
