Potential clinical role of fluorodeoxyglucose-positron emission tomography in assessing primary or secondary lymphomas of the parotid gland

Background: We have reviewed the utility of fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging for clinical management of primary parotid lymphoma (by applying strict criteria of primary extranodal involvement by this disease) as well as of cases in which spread of the disease to the parotid gland had occurred as a consequence of primary nodal disease. Patients and Methods: A total of 9 cases of parotid lymphoma (5 primary parotid lymphoma and 4 cases of combined nodal/extranodal lymphoma with parotid involvement) were identified and analyzed for this study. A retrospective review of the clinical records, radiologic data, and pathology results was carried out for assessment of the natural course and FDG-PET results in this disease. These patients had undergone conventional whole-body FDG-PET or PET/computed tomography for initial or posttherapy monitoring purposes. Results: All cases in both subgroups had unilateral parotid involvement. Fluorodeoxyglucose uptake was focal, and visual assessment was sufficient to detect the disease in all the cases with a sensitivity of 100% in primary and secondary lymphoma of the parotid, independent of the histologic subtypes. The maximum standard uptake value in untreated cases of diffuse large B-cell lymphoma and follicular non-Hodgkin lymphoma of parotid was higher (10.4 and 10.2, respectively) than that of primary parotid marginal zone lymphoma (5.2). Postchemotherapeutic remission was correctly determined by PET in all 3 patients who underwent chemotherapy. The parotid involvement was noted at diagnosis in 2 cases and in the remaining ones up to 30 months after initial diagnosis. Fluorodeoxyglucose uptake was focal and distinct in all cases, and in 1 patient with a parotid nodule as small as 0.5 cm, the lesion was clearly visualized. The maximum standard uptake values in the posttreatment scenario varied from 1.3 to 1.9, which are within the range of what has been observed in the normal parotids. In 4 of 5 patients who underwent treatment monitoring, complete metabolic response in PET was noted in advance of size criteria by radiologic techniques for complete response. Conclusion: Despite the known physiologic FDG uptake in parotid glands, FDG-PET appears to be of potential value in managing patients with parotid lymphoma in various stages of disease, including diagnosis and monitoring for therapeutic response.