False positive 131I total body scan due to bilateral polycystic renal disease

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.

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.

131I Whole-Body Scan Incidental Uptake Due to Spermatocele

A 46-year-old man with papillary thyroid cancer post total thyroidectomy was referred for post radioiodine (I) whole-body scan. Whole-body images revealed intense I uptake in the bed thyroid and a focal abnormal uptake in the testicular area. Subsequent SPECT/CT demonstrated that the focal uptake corresponded to the left epididymis, and the pathology report revealed a spermatocele with no immunohistochemical features for thyroid tissue. Many cases of unexpected radioiodine uptake have been reported, and spermatocele could be counted for another possibility of incidental I uptake despite an unclear mechanism.

False positive diagnosis on (131)iodine whole-body scintigraphy of differentiated thyroid cancers

(131)Iodine is used both to ablate any residual thyroid tissue or metastatic disease and to obtain whole-body diagnostic images after total thyroidectomy for differentiated thyroid cancer (DTC). Even though whole-body scan is highly accurate in showing thyroid residues as well as metastases of DTC, false positive results can be found, possibly leading to diagnostic errors and unnecessary treatments. This paper reviews the physiological and pathological processes involved as well as the strategy to recognize and rule out false positive radioiodine images.

A solitary large radioiodine accumulative lung lesion in high-dose 131i therapeutic scan: bronchial atresia with mucocele

We reported a large radioiodine accumulative lung lesion on I therapeutic whole-body scan performed in a 50-year-old woman for thyroid cancer ablation therapy. Previously, her chest radiography and contrast-enhanced chest CT images showed bronchial atresia in the left upper lobar bronchus and mucus-filled dilated distal bronchus. Bronchial mucocele was confirmed by CT-guided percutaneous transthoracic needle aspiration. Bronchial atresia is a rare congenital abnormality associated with the mucocele.

Radioiodine uptake in a renal cyst mimicking a metastasis in a patient affected by differentiated thyroid cancer: case report and review of the literature

We report a 55-year-old man affected by differentiated thyroid carcinoma with lymph nodes metastases. After conventional levothyroxine withdrawal, the patient underwent thyroid remnant ablation by oral administration of radioiodine-131 ablative activity (3700 MBq). 7 days later, post-therapy whole body scan (pWBS) demonstrated thyroid remnant and showed a large area of abnormal radioiodine uptake located in the posterior left upper abdomen. Ultrasonography of the abdominal region revealed a cyst in left kidney corresponding to the focal radioiodine uptake. On the same day, 131I static images of the posterior upper abdomen obtained before and after administration of furosemide, showed that radioiodine uptake in the lesion was markedly lower after diuretic administration, indicating that radioiodine accumulation in the renal cyst is linked to an active secretory process by the renal tubule. Due to its non-negligible frequency, renal cyst should be taken into account in DTC patients as a potential pitfall at 131I pWBS.

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

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.

Cystic ovarian metastasis from papillary thyroid carcinoma: a case report

Ovarian metastasis from a primary thyroid carcinoma is rare. In this report we describe a woman who manifested the unusual occurrence of metastases of papillary thyroid carcinoma to the ovary. Both clinically and pathologically, such a presentation can be difficult to distinguish from benign cystic neoplasms of the ovary or cystic struma ovarii.