The interpretation of 131I scans in the evaluation of thyroid cancer, with an emphasis on false positive findings

Abstract

Radioiodine has aided the management of differentiated thyroid cancer for several decades. Most thyroid cancers retain the ability to trap iodine, and radionuclides of iodine can be used both diagnostically and therapeutically. The availability of sensitive diagnostic tests, coupled with the ability to deliver targeted therapy, gives physicians the ability to manage thyroid cancer better than with any other type of cancer. The correct interpretation of radioiodine scans is critical in the appropriate management of patients with thyroid cancer. False positive findings do occur. A radioiodine scan showing abnormal uptake outside the thyroid bed must be studied carefully and alternative reasons for the finding must be considered. The scan should be analysed systematically. Is there residual thyroid? If so, what is the 48 or 72 h neck uptake? Radioiodine uptake in the salivary glands, stomach, gastrointestinal and urinary tracts should be acknowledged as physiological. Diffuse uptake is seen in the liver in most patients with functioning thyroid at the time of their post-therapy scan. When there is uptake of the radioiodine outside these regions, contamination must be considered. A variety of cases illustrating true positive, true negative, and false positive findings is presented in this review, and the causes and consequences of misinterpretation of radioiodine scans are discussed.

Ovarian Teratoma Mimicking Metastasis on I-131 Scan : A Case Report

“…Over time, there have been several reports of falsepositive radioiodine uptake in other organs and their associated diseases, as well as in other pathologic processes [3][4][5][6]. Here, we report a case of ovarian teratoma mimicking metastasis from thyroid cancer on whole body I-131 scan.…”

Post-Therapeutic I-131 Whole Body Scan in Patients with Differentiated Thyroid Cancer

“…Carliscle et al summarized false positive findings (Carlisle et al, 2003). I-131 uptake can be seen in the nose, salivary glands, mouth, thyroid bed, lactating breast, liver, gall bladder, stomach, esophagus and sweat ( Figure 6).…”

“…I-131 uptake can be seen in the nose, salivary glands, mouth, thyroid bed, lactating breast, liver, gall bladder, stomach, esophagus and sweat ( Figure 6). Physiologic uptake of I-131 in the salivary glands, nasal mucosa, gastric mucosa, colon, mammary glands and choroid plexus is due to the NIS presence in these tissues (Carlisle et al, 2003;Riedel et al, 2001). Thymic uptake is rare, there is a report that the incidence of thymic uptake was 1-1.2% of cases (Davidson & McDougall, 2000) (Figure 7).…”

“…Thymic uptake is rare, there is a report that the incidence of thymic uptake was 1-1.2% of cases (Davidson & McDougall, 2000) (Figure 7). Diffuse hepatic uptake of I-131 is rarely found due to occult hepatic metastases but more commonly due to the hepatic de-ionization and conjugation of I-131 which was not incorporated into the thyroid hormone (Carlisle et al, 2003). Chung et al investigated hepatic uptake on DxWBS or RxWBS.…”

“…There are some reports I-131 false positive uptake in other pathologic condition unrelated to thyroid cancer: tracheostomy site, bronchiectasis, pulmonary inflammatory disease, pleural effusion, salivary gland tumor, some other carcinoma such as adenocarcinoma, squamous carcinoma, Barrett's esophagus, Meckel's diverticulum (Ain & Shih, 1994;Berquist et al, 1975;Caplan et al, 1987;Carlisle et al, 2003;Fernandez-Ulloa et al, 1976;Hoschl et al, 1988;Misaki et al, 1994;Mitchell et al, 2000;Muratet & Giraud, 1996), and so on. (Figure 9) …”