An unusual case of a false-positive iodine-131 whole body scan in a patient with papillary thyroid cancer

Reappraising the Diagnostic Accuracy of Post-Treatment Whole-Body Scans for Differentiated Thyroid Carcinoma

Initial treatment for differentiated thyroid carcinoma (DTC) often consists of surgery and the administration of radioiodine. In this context, post-treatment Whole-Body Scans (ptWBS) are currently recommended, but data on its diagnostic accuracy are rare. The aim of the study was to evaluate the performance of ptWBS for distant metastasis in DTC patients. We included DTC patients who received radioiodine and underwent ptWBS between 2009-2015. The medical data were independently reviewed by two specialists to evaluate the concordance of positive distant ptWBS uptake and distant metastasis documented by imaging exams (gold standard). We studied 268 DTC patients. The mean age was 46±16 years (82% women), and papillary thyroid carcinoma was diagnosed in 87% of the patients. The median tumor size was 2.7 cm, 40% had lymph node involvement, and 11% had distant metastasis. Twenty-eight patients (10%) had distant ptWBS uptake, and nine of them (32%) were false-positives. In addition, nine false-negative ptWBS uptakes were identified. The overall performance of ptWBS showed 68% sensitivity and 96% specificity with significantly different performance according to the American Thyroid Association (ATA) risk groups. While the ptWBS performance for ATA low-intermediate-risk showed 29% sensitivity, 97% specificity, and Kappa of 0.19, the ATA high-risk group ptWBS displayed high sensitivity (82%), specificity (100%), and good agreement (Kappa 0.74). ptWBS is useful for a subgroup of ATA high-risk DTC patients. The overall poor performance of ptWBS suggests that it should be reconsidered for routine use in ATA at low to intermediate risk: the exam has little value to this subgroup.

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.

Epiphrenic diverticulum: potential pitfall in thyroid cancer iodine-131 scintigraphy

Unusual features of iodine-131 uptake during thyroid cancer scintigraphy may lead to a false-positive diagnosis of residual or recurrent malignancy and associated metastasis. Radiographic or cross-sectional imaging correlation should help to differentiate truly functioning thyroid lesions from physiological or artifactual tracer accumulation. The authors present a case of iodine-131 mediastinal uptake from an esophageal epiphrenic diverticulum.

Unusual patterns of I-131 contamination

Whole body imaging with radioiodine can detect functioning metastases, which can often be effectively treated with appropriate amounts of radioiodine. Non-physiologic I-131 uptake detected on images is usually interpreted as suggesting functioning thyroid metastases. However, extra-thyroidal I-131 accumulation does not always imply thyroid cancer metastases and has been reported on many occasions, including various non-thyroidal neoplasms, and contamination by body secretions. In order to avoid unnecessary therapeutic interventions it is extremely important to properly distinguish false-positive sites of I-131 localization. Three patients with unusual radioiodine contamination patterns, either presented for the first time or rarely presented in the existing literature, were reported. Reported cases consist of contamination in hair (due to styling hair with sputum), contamination in neck (due to drooling during sleep) and, contaminated chewing gum. False positive contamination sources were clarified by careful examination of patients and further images when necessary.

Hiatal hernia in iodine-131 scintigraphy: a potential cause of false-positive midline thoracic uptake

There are occasional reports of a hiatal hernia demonstrating thoracic uptake on I-131 scintigraphy. This is a cause of a potential false-positive appearance mimicking a pulmonary or mediastinal metastasis. Hiatal hernia is 1 of a number of causes of false-positive I-131 whole-body scans. Although previous case reports have demonstrated uptake to lie to the left of the midline, this case is slightly unusual in view of the midline appearance of the uptake. Although this appearance could be seen with mediastinal, pulmonary, or prevertebral metastases, hiatal hernia should be considered in the differential diagnosis of uptake in the thoracic midline on I-131 scintigraphy.

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.

Serum thyroglobulin measurement. Utility in clinical practice

Serum thyroglobulin measurement has greatly facilitated the clinical management of patients with differentiated thyroid cancer and a variety of other thyroid disorders. Thyroglobulin autoantibodies remain a significant obstacle to the clinical use of thyroglobulin measurement. The interpretation of any given thyroglobulin value requires the careful synthesis of all pertinent clinical and laboratory data available to the clinician. The diagnostic use of rhTSH-stimulated thyroglobulin levels has greatly facilitated the follow-up of low-risk patients with thyroid cancer. Although the measurement of thyroglobulin mRNA from peripheral blood is likely to affect the future management of these patients, it is expected that serum thyroglobulin measurement will continue to have a principal role in the care of patients with differentiated thyroid cancer.

Unusual false-positive radioiodine whole-body scans in patients with differentiated thyroid carcinoma

Radioiodine whole-body imaging is the most accurate method in the diagnosis of metastases from differentiated thyroid cancer. However, false-positive images rarely occur. The authors report unusual cases of thymic hyperplasia and post-traumatic skull changes mimicking mediastinal, skull, or cerebral metastases. Nonthyroidal causes were diagnosed by other radionuclide studies (bone and brain scintigraphy) and CT scans. Follow-up and undetectable thyroglobulin levels helped confirm the benign cause.

False-positive thyroid cancer metastasis on whole-body radioiodine scanning due to retained radioactivity in the oesophagus

In patients with differentiated thyroid cancer, radioiodine uptake in the mediastinal area most often indicates thyroid cancer metastasis. We review 15 radioiodine whole-body scans showing 19 mediastinal artefacts that mimicked lymph node or spinal metastasis. The artefacts disappeared on delayed images after eating and drinking (17) or on studies repeated within 1 week (2), suggesting their oesophageal origin. No patient had clinical oesophageal or gastric disease. Only two artefacts were linear; 12 were focal and five were diffuse. Twelve artefacts were better seen on anterior views (nine in the upper, two in the middle and one in the lower mediastinal area), whereas seven were better seen on posterior views (two in the upper, two in the middle, and three in the lower mediastinal area). The 15 scans were identified from about 1000 scans performed over 24 months in our centre. We conclude that the transient presence of radioiodine in an apparently normal oesophagus may not uncommonly mimic mediastinal lymph node or spinal metastases from thyroid cancer and that its scintigraphic presentation is variable.

The role of functional imaging in neoplasms of the thyroid

Iodine-123 and Iodine-131 have suitable physical properties that enable them to be used for functional imaging of the thyroid. Iodine-123 is used for routine testing for hyperthyroidism and thyroid nodules, whereas I-131, which has a longer half-life, is used for whole body imaging for detecting metastatic thyroid cancer in patients who have undergone thyroidectomy. The radionuclides of iodine are trapped and organified like nonradioactive iodine. In contrast, technetium as pertechnetate is trapped by the thyroid and can be used for imaging immediately after intravenous injection. There can be differences in scintiscans made in the same patient using radioiodine vs. technetium. Thallium is a useful adjuvant imaging agent for thyroid cancer. It should be stressed that correlation with the clinical findings and biochemical thyroid function tests are very important when evaluating thyroid scintiscans.