False-positive radioiodine uptake in a functional ovarian cyst in a patient treated with total thyroidectomy for papillary cancer

Radioiodine whole body scan pitfalls in differentiated thyroid cancer

PURPOSE

whole body scan (WBS) performed following diagnostic or therapeutic administration of I-131 is useful in patients with differentiated thyroid carcinoma. However, it can be falsely positive in various circumstances. We aimed to report a series of pitfalls in a clinical perspective.

METHODS

A search in the database PubMed utilizing the following terms: "false radioiodine uptake" and "false positive iodine 131 scan" has been made in January 2023. Among the 346 studies screened, 230 were included in this review, with a total of 370 cases collected. Physiological uptakes were excluded. For each patient, sex, age, dose of I-131 administered, region and specific organ of uptake and cause of false uptake were evaluated.

RESULTS

370 cases of false radioiodine uptake were reported, 19.1% in the head-neck region, 34.2% in the chest, 14.8% in the abdomen, 20.8% in the pelvis, and 11.1% in the soft tissues and skeletal system. The origin of false radioiodine uptake was referred to non-tumoral diseases in 205/370 cases (55.1%), benign tumors in 108/370 cases (29.5%), malignant tumors in 25/370 cases (6.7%), and other causes in 32/370 cases (8.7%).

CONCLUSIONS

WBS is useful in the follow-up of patients with differentiated thyroid carcinoma, however it can be falsely positive in various circumstances. For this reason, it is critically important to correlate the scintigraphic result with patient's medical history, serum thyroglobulin levels, additional imaging studies and cytologic and/or histologic result.

Aberrant Radioactive Iodine Uptake in Simple Ovarian Cyst: A Rare Finding

I-131 whole body scan and therapy play an important role in the follow-up of differentiated thyroid carcinoma patients for the detection of residual thyroid tissue and metastatic disease. However, various false-positive findings have been reported in the literature which can appear as metastases. Here, we present one such case, in which an I-131 posttherapy scan revealed false-positive radioactive iodine uptake which localized to a simple ovarian cyst.

False-Positive Radioiodine Uptake in Simple Ovarian Cyst in a DTC Patient: A Case Report

Abnormal radioildine uptake can be caused by various pelvic lesions in differentiated thyroid cancer patient. Here we presented an abnormal uptake in the left side of the pelvic cavity on postablative I-131 scintigraphy in a 51-year-old woman with history of stage T1aN1M0 papillary thyroid cancer. The SPECT/CT fused imaging revealed the lesion in the left ovary. Laparoscopic bilateral adnexectomy showed a left ovarian mass (5 cm) and pathologic finding showed a simple ovarian cyst. The nonstimulated Tg immediately decreased to 143 ng/ml after bilateral adnexectomy 3 days later and to 0.109 ng/ml after 4-month follow-up. Timely intervention measures are very necessary for patients with ovarian cyst with abnormally elevated Tg level.

Causes of False-Positive Radioactive Iodine Uptake in Patients with Differentiated Thyroid Cancer

Purpose

Radioactive iodine (RAI) whole-body scan is a sensitive imaging modality routinely used in patients with differentiated thyroid cancer to detect persistent and recurrent disease. However, there can be false-positive RAI uptake that can lead to misdiagnosis and misclassification of a patient’s cancer stage. Recognizing the causes of false positivity can avoid unnecessary testing and treatment as well as emotional stress. In this review, we discuss causes and summarize various mechanisms for false-positive uptake.

Recent Findings

We report a patient with differentiated thyroid cancer who was found to have Mycobacterium avium complex infection as the cause of false-positive RAI uptake in the lungs. Using this case example, we discuss and summarize findings from the literature on etiologies of false-positive RAI uptake. We also supplement additional original images illustrating other examples of false RAI uptake.

Summary

False-positive RAI uptake may arise from different causes and RAI scans need to be interpreted in the context of the patient’s history and corresponding cross-sectional imaging findings on workup. Understanding the potential pitfalls of the RAI scan and the mechanisms underlying false uptake are vital in the care of patients with differentiated thyroid cancer.

Thyroid detectives: on the trail of Munchausen's syndrome

Thyrotoxicosis factitia, a disorder frequently seen in young or middle-aged women with psychological disorders, most commonly results from surreptitious ingestion of excess thyroid hormones. In most patients, diagnosis is relatively straightforward and depends on the demonstration of biochemical thyrotoxicosis, suppressed endogenous thyroid function and absence of clinical features of underlying thyroid disease. However, at times, confounding factors can make the diagnosis particularly challenging and necessitate the investigating physician to don the detective's cap to get to the root of the problem. We discuss a patient whose diagnosis was reached with ingenuity after considerable effort from four endocrinologists having a total experience of 37 years in their field.

Unexpected False-positive I-131 Uptake in Patients with Differentiated Thyroid Carcinoma

Objective:

Radioiodine is the most specific radionuclide for differentiated thyroid carcinoma (DTC) imaging. Despite its high specificity and sensitivity, false-positive I-131 uptake could be seen on whole body scan (WBS) that may lead to misdiagnosis and unnecessary radioiodine treatment. In this study, we aimed to present the I-131 WBS and concomitant single photon emission computed tomography/computed tomography (SPECT/CT) images of unexpected false-positive radioiodine uptake along with the patients’ clinical outcomes and the contribution of SPECT/CT imaging.

Methods:

I-131 WBSs of 1507 patients with DTC were retrospectively reviewed, and anticipated I-131 uptakes (like in breasts or thymus) were excluded from the study. The unexpected false-positive I-131 uptakes with concomitant SPECT/CT imaging were included in the study.

Results:

Twenty-one patients had 23 unexpected I-131 uptakes on WBS and concomitant SPECT/CT imaging. The vast majority (87%) of these cases were seen on post-therapeutic I-131 WBS. Most of the false-positive I-131 uptakes could be explained by SPECT/CT and radiologic findings, and were secondary to non-thyroid conditions (bronchiectasis, lung infection, subcutaneous injection into gluteal fatty tissue, aortic calcification, benign bone cyst, vertebral hemangioma, recent non-thyroid surgical procedure site, rotator cuff injury, mature cystic teratoma and ovarian follicle cyst). However, the possible reasons of 9 false-positive I-131 uptakes could not be explained by radiologic findings.

Conclusion:

We suggest that false-positive I-131 uptake and its underlying mechanisms (inflammation, trapping, increased perfusion, etc.) must be kept in mind in patients with thyroid cancer and unexpected findings must be considered together with serum thyroglobulin levels, SPECT/CT and radiologic findings in order to avoid misdiagnosis and unnecessary radioiodine treatment.

Pictorial Review of False-Positive Results on Radioiodine Scintigrams of Patients with Differentiated Thyroid Cancer

Radioiodine has served an important role in the diagnostic workup and treatment of patients with differentiated thyroid cancer for more than 6 decades. The interpretation of radioiodine scintigraphic studies should be performed in conjunction with a comprehensive history, histopathologic correlation, and pertinent laboratory values, as well as correlation with available anatomic images and the findings from physical examination. A thorough understanding of the physiology and biodistribution of radioiodine is critical when interpreting radioiodine scintigraphic studies to avoid misinterpretation of physiologic and nonthyroid pathologic variants as thyroid cancer metastases. Differentiating a false-positive finding from a true metastasis on pretherapy radioiodine scintigrams is important to determine the appropriate radioiodine treatment dose. The correct interpretation of posttherapy radioiodine scintigraphic studies is also important to determine if repeat radioiodine treatment will be necessary and for the future clinical and imaging followup of the patient. A variety of different factors, such as the presence of the sodium-iodide symporter and the passive diffusion or retention of radioiodine in normal and pathologic structures, can result in false-positive results on radioiodine scintigrams. Numerous false-positive findings have been reported in the literature and are further demonstrated with the increasing availability of single photon emission computed tomography (SPECT) integrated with computed tomography (CT) as true dual-modality imaging (SPECT/CT). SPECT/CT has been documented to be of incremental value in the accurate anatomic localization and characterization of radioiodine uptake as false-positive findings, particularly in cases with discordant findings of a low serum thyroglobulin level but positive findings on radioiodine whole-body planar scintigrams. The objectives of this review are to describe the physiology and biodistribution of radioiodine and to provide examples of false-positive results on radioiodine scintigrams, with clinical and anatomic correlation, in the following categories of radioiodine uptake: functional uptake secondary to sodium-iodide symporter expression, radioiodine retention, nonthyroid neoplasms, inflammatory or infectious uptake, contamination, and other causes. ^©RSNA, 2017.

Urinary Iodine Concentrations in Cancer Patients

Background: It has been suggested that incidence of some cancers, especially examples in the breast and stomach may be influenced by the iodine intake. However, only few studies are available at present. Therefore, we have conducted the present assessment of iodine status in Iranian patients diagnosed with a malignancy. Materials and Methods: This cross-sectional study was conducted in 85 patients diagnosed with different types of cancer at Shahid Sadoughi Hospital, Yazd, Iran. The method used was based on the Sandell–Kolthoff reaction. Results: The median urinary iodine concentration (UIC) was 17.4 μg/L, with ≤20 μg/L indicative of severe iodine deficiency. According to the WHO/IC C IDD/UNIC EF classification, 88.1%, 7.1% and 2.4% of patients had a UIC <20 (severe), 20–49 (mild), and 50–99 μg/L (moderate), respectively. There was no statistically significant differences in UIC between men and women. Conclusion: The UIC values indicate that Iranian cancer patients were seriously iodine deficient according to WHO/UNIC EF/ IC C IDD, and that this is a suitable index to assess iodine status in Iranians. Daily consumption of salt fortified with iodine or other approaches to increase intake might be effective strategies for prevention or reduction of malignancies.

Unusual False Positive Radioiodine Uptake on (131)I Whole Body Scintigraphy in Three Unrelated Organs with Different Pathologies in Patients of Differentiated Thyroid Carcinoma: A Case Series

Three cases with unusual false positive radioiodine uptake in three different organs and pathologies (infective old fibrotic lesion in the lung, simple liver cyst, and benign breast lesion) on iodine-131 (¹³¹I) whole body scintigraphy. Clinicoradiological correlation was undertaken in all three cases and the pathologies were ascertained. In all the three cases, single-photon emission computerized tomography-computed tomography (SPECT-CT) and ancillary imaging modalities were employed and were helpful in arriving at the final diagnosis.