Diffuse and diffuse-plus-focal uptake in the thyroid gland identified by using FDG-PET: prevalence of thyroid cancer and Hashimoto's thyroiditis

Abstract

Our results suggest that although diffuse FDG uptake usually indicates Hashimoto's thyroiditis, the risk of thyroid cancer must be recognized in both diffuse FDG uptake and diffuse-plus-focal FDG uptake on PET scan.

The Role of 18F-Fluorodeoxyglucose Positron Emission Tomography in Thyroid Neoplasms

“…The SUV max of chronic thyroiditis patients (2.76 Ϯ 1.24) was significantly higher than that of normal variants (1.99 Ϯ 0.63; p ϭ .002) [31]. Kurata et al [21] reported that the mean SUV max was 3.5 (range, 1.6 -7.8) in 25 patients with diffuse FDG uptake and a USG diagnosis of Hashimoto's thyroiditis. The mechanism of FDG uptake in Hashimoto's thyroiditis is not well understood.…”

“…Other common differential diagnoses for the diffuse uptake pattern include chronic thyroiditis and Graves' disease [11,18]. In a series reported by Kurata et al [21], they found that, of 1,626 patients undergoing an FDG-PET scan, all 25 (1.5%) patients with diffuse uptake turned out to have Hashimoto's thyroiditis. Kang et al [20] showed that when both the focal and diffuse FDG uptake patterns were correlated with ultrasonography (USG) findings, only 59.5% of those with a diffuse uptake pattern had a corresponding nodule in the lobe on USG, whereas Ͼ99% of those with a focal uptake pattern had a corresponding nodule on USG.…”

“…Kang et al [20] examined 15 patients with multifocal uptake and found that all had thyroid malignancy on histology. Kurata et al [21] reported that two of four patients (50%) with a diffuse plus focal FDG uptake pattern had papillary thyroid carcinoma (PTC) with a background of Hashimoto's thyroiditis. In other words, although the data remain limited, the multifocal and diffuse plus focal patterns warrant further investigation and should not be confused with the diffuse uptake pattern because they probably carry a similar, if not greater, malignancy risk as the focal pattern [22].…”

Incidental 18F-FDG uptake in the thyroid in patients diagnosed with PET/CT for other malignancies

“…In fact, many of these patients had already been treated with Lthyroxin before performing the scan. Although diffused 18 F-FDG uptake seems to be quite accurate in confirming the diagnosis of Hashimoto thyroiditis [19,21], a risk of thyroid cancer in both diffuse and combined 18 F-FDG uptake should be kept in mind [18,22]. Additionally, the presence of Hashimoto disease with a large goitre may impair the diagnostic value of 18 FDG PET in primary thyroid lymphoma [20].…”

Clinical Significance of Diffuse 18F-FDG Uptake in Residual Thyroid Gland after Unilateral Thyroid Lobectomy

“…A thyroid lesion with focal 18 F-FDG uptake is likely to be malignant [5][6][7][8][9], whereas diffusely increased uptake in the thyroid gland is associated with several thyroid disorders including chronic thyroiditis, Graves' disease, and diffuse goiter [9][10][11][12][13]. Several studies have reported that incidence of diffusely increased 18 F-FDG uptake in the thyroid gland was 0.6-3.3%.…”