Fluorodeoxyglucose positron emission tomography (FDG-PET) and PET/computed tomography imaging characteristics of thyroid lymphoma and their potential clinical utility

Abstract

Background: A relative paucity of data exists in the literature with regard to the utility of fluorodeoxyglucose positron emission tomography (FDG-PET) imaging in the clinical management of patients with primary lymphoma of the thyroid gland (PTL). Purpose: To explore the FDG-PET imaging characteristics and their potential role in PTL, and to compare the results with anatomical imaging modalities. Material and Methods: Patients with thyroid lymphoma who had undergone whole-body FDG-PET or PET/computed tomography (CT) during their course of the disease were identified by examination of case records. PET scans were reevaluated, and maximum standardized uptake value (SUVmax) was calculated and used as the semiquantitative measure of FDG uptake for this analysis. CT and/or magnetic resonance imaging (MRI) studies carried out within 1 week of FDG-PET scan and without any therapeutic intervention between the two studies were considered for the purpose of comparison. A total of six patients with 20 studies (14 FDG-PET and six PET/CT examinations) were identified following the criteria. All patients were female (age 16–83 years). Among these, five were proven to have PTL. Two patients had localized PTL (stage IE), two patients had associated regional nodal involvement (IIE), and one patient had associated nodal involvement on both sides of the diaphragm (IIIE) at presentation. Except for one patient with follicular B-cell lymphoma, all others were diffuse large-B-cell lymphoma (DLBCL) subtype. Results: Avid FDG uptake was observed in both cases of untreated PTL, with SUVmax of 23 and 7.6, respectively. One patient showed focal FDG uptake (SUVmax 6.7) in the thyroid in the setting of a responding abdominal non-Hodgkin lymphoma (NHL) and was subsequently proven as adenomatous nodule with Hurthle cell changes. Following successful therapy, SUVmax declined consistently with improvement in disease status. In one patient, complete response was noted earlier by FDG-PET compared to CT. Disease recurrence was detected earlier by FDG-PET compared to CT in two patients with increased FDG activity in both thyroid lobes without any corresponding CT abnormality. Conclusion: FDG-PET is a useful and sensitive modality for assessing disease activity in thyroid lymphoma. Its ability to detect disease recurrence was found to be superior compared to CT in two patients.