18F-PET/CT imaging of metastasis to the thyroid gland: Imaging findings and effect on patient management

Abstract

Purpose While metastasis to the thyroid from a primary cancer remote to the thyroid is uncommon, current imaging techniques have improved detection of these intrathyroid metastases. The purpose of this study was to evaluate the 18F-PET/CT appearance of intrathyroid metastases and assess the impact of detection on patient management. Methods The 18F-PET/CT appearance of intrathyroid metastasis, including standardized uptake value (SUV), disease extent, and the effect on patient management following diagnosis were retrospectively reviewed. Inclusion criteria included 18F-PET/CT imaging and diagnosis of the intrathyroid metastasis matching the remote primary tumor. Results Intrathyroid metastasis were detected in 24 patients. The intrathyroid metastases presented on 18F-PET/CT as focal nodular uptake (n = 21), multiple nodular uptake (n = 2), or diffuse uptake/infiltration of the thyroid gland (n = 1). The SUV ranged between 3.9 and 42 (median 12.5 ± 7.5); in 2 patients, the FDG-avidity was minimal. On 18F-PET/CT, distant metastases were present outside the neck (n = 18), or limited to the neck (n = 6). In 2 of these 6 patients, the thyroid was the only site of metastatic disease. Due to the metastatic disease, the therapy was changed in 23 of 24 patients; 1 patient was lost to follow-up. Conclusion In any patient with a previous or current history of an extrathyroid malignancy, an 18FDG-avid thyroid mass or diffuse infiltration of the thyroid on 18F-PET/CT should be considered a potential intrathyoid metastasis until proven otherwise. Knowledge of an intrathyroid metastasis may impact patient management, especially if the thyroid or neck are the only sites of metastatic disease.

Role of imaging in clinically occult isolated intrathyroidal metastasis from squamous cell carcinoma of tongue: An unusual case series

“…Intrathyroidal metastases present on 18F-PET/CT predominately as high-grade FDG avid solitary nodules, but can also occur as multiple nodules; this is in contradiction to the normal thyroid gland that usually shows low or absent 18F-FDG uptake. [ 7 8 9 ] Hence, in our case series also, they were picked up incidentally on PET-CT study. The risk of malignancy is as high as 63.6% in thyroid lesions with focal uptake.…”

“…Clinical findings may be subtle, detection of an intra-thyroid metastasis from an extrathyroid primary head and neck tumor has improved significantly with current imaging technique 18-fluorodeoxyglucose positron emission tomography-computed tomography (18-FDGPET-CT) scan. [ 7 8 9 ]…”

Rare Metastasis of Gastric Cancer to the Thyroid Gland: A Case Report and Review of Literature

“…For the detection of metastatic disease, PET-CT scans are an extremely useful diagnostic tool (29). In many cases, intrathyroid metastatic tumors are themselves discovered via PET-CT (15,(30)(31)(32)(33). If the primary tumor can be completely removed in the absence of other organ metastases or if the metastases can be removed simultaneously, the surgical treatment of thyroid metastases should be considered.…”

Incidental thyroid uptake on PET scanning: epidemiology, clinical significance, and management challenge

“…This is significant as it may prompt a change in prognosis and treatment. A meta-analysis identified 1.1% of PET-detected thyroid incidentalomas to represent metastatic disease and a 19.8% overall malignancy rate (with 15.4% representing papillary thyroid carcinoma) [64] . Metastases to the thyroid were described with solitary focal, multiple focal, and diffuse patterns of FDG avidity [65] .…”

“…Multiple 68 Ga-DOTA peptides have been studied that have a variable affinity for somatostatin receptor subtypes [79] . 68 Ga-and 64 Cu-DOTATATE are currently the only peptides clinically approved by the FDA in the USA for PET imaging. Physiologic uptake has been noted in the pituitary, thyroid, spleen, liver, adrenal glands, head of the pancreas, and urinary tract [80] .…”