Radioactive iodine uptake by a large cell undifferentiated bronchogenic carcinoma

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.

Radioiodine Uptake in Incidentally Detected Neuroendocrine Tumor: Correlative Imaging With FDG PET/CT and 68 Ga-DOTATATE PET/CT

ABSTRACT

Radioiodine whole-body scintigraphy has long been used for detection of differentiated thyroid carcinoma with high avidity in functioning thyroid tissues. However, uptake is not completely specific, and "false-positive" uptake in nonthyroidal tumors have rarely been reported. Herein, we present a case of incidentally detected neuroendocrine tumor showing high radioiodine uptake initially suspected to be thyroid metastasis. Correlative imaging with FDG PET/CT and 68 Ga-DOTATATE PET/CT is presented, and literature survey is discussed. We conclude that neuroendocrine tumor should be added to the reported list of neoplasms that can show "false-positive" uptake representing a potential interpretative pitfall.

Primary lung cancer with radioiodine avidity: A thyroid cancer cohort study

BACKGROUND

A proportion of lung cancers show sodium/iodide symporter (NIS) expression. Lung cancers with NIS expression may uptake radioiodine (RAI) and show RAI-avid lesions on RAI scan for differentiated thyroid cancer (DTC) surveillance.

AIM

To investigate the possibility of RAI uptake by lung cancer in a cohort with thyroid cancer.

METHODS

RAI-avid lung cancers were analyzed using a prospectively maintained database of patients with thyroid cancer who were registered at a medical center between December 1, 1976 and May 28, 2018. NIS expression in lung cancer was assessed using immunohistochemical staining.

RESULTS

Of the 5000 patients with thyroid cancer from the studied dataset, 4602 had DTC. During follow-up, 33 patients developed primary lung cancer. Of these patients, nine received an iodine-131 (¹³¹I) scan within 1 year before the diagnosis of lung cancer. One of these nine lung cancers was RAI-avid. NIS expression was evaluated, and three of the eight available lung cancers revealed NIS expression. The proportions of lung cancer cells with NIS expression were 60%, 15%, and 10%. The RAI-avid lung cancer had the highest level of expression (60%). The RAI-avid lung cancer had a spiculated border upon single-photon emission computed tomography/computed tomography, which led to an accurate diagnosis.

CONCLUSION

A proportion of lung cancer demonstrates NIS expression and is RAI-avid. Clinicians should be aware of this possibility in the interpretation of RAI scintigraphy.

Intrathoracic toxic thyroid nodule causing hyperthyroidism with a multinodular normal functional cervical thyroid gland

Radionuclide scintigraphy with I-131 and Tc-99m pertechnetate ((99)mTc04) has been widely used in detecting toxic nodules. Intrathoracic goiter usually presents as an anterior mediastinal mass. Mostly the connection between intrathoracic mass and the cervical thyroid gland is clearly and easily identified occurring as a result of inferior extension of thyroid tissue in the neck, which is called as secondary intrathoracic goiter. Completely separated, aberrant or in other words primary intrathoracic goiters arise as a result of abnormal embryologic migration of ectopic thyroid closely associated with aortic sac and descend into the mediastinum. Intrathoracic goiters are generally nontoxic nodules existing with mass effect without causing hyperthyroidism. However, mostly reported cases had enlarged thyroid glands in the neck. This report demonstrates the usefulness of I-131 and (99)mTc04 scintigraphy for detecting intrathoracic goiter causing hyperthyroidism with a normal functioned cervical thyroid gland.

False-positive 131I whole-body scan in well-differentiated thyroid cancer patient with respiratory bronchiolitis

(131)I whole-body scan is performed during treatment and follow-up after radioiodine treatment to detect functioning thyroid remnant and metastatic lesions in differentiated thyroid carcinoma (DTC). False-positive scans are rare, but may cause a potential pitfall by misleading to unnecessary radiation exposure from inappropriate radioiodine treatment. We report a case of papillary thyroid cancer patient with false-positive (131)I scan in the lung due to pulmonary bronchiolitis. Clinical correlation and imaging characteristics obtained from additional SPECT/CT images are very helpful to indicate this lesion as a benign condition.

Bronchoalveolar carcinoma of lung masquerading as iodine avid metastasis in a patient with minimally invasive follicular carcinoma of thyroid

A 52-year-old man with follicular thyroid carcinoma was administered 182 mCi of radioiodine (I-131) a month after total thyroidectomy. Post-therapy scan revealed diffuse uptake of radioiodine in the apical left lung. CT-guided biopsy of this mass revealed mucinous bronchoalveolar carcinoma. Immunohistochemistry for thyroglobulin was negative. An FDG PET scan showed avid uptake in the lung mass. Surgery was ruled out, so he was given chemotherapy, without benefit. The lesion continued to show I-131 uptake even while on daily T3 substitution, suggesting that the mass was thyroid stimulating hormone-independent. Because the mass showed I-131 uptake and chemotherapy was not beneficial, it was decided to treat with I-131. He was continued on T3 substitution therapy and was given 209 mCi of I-131. Follow-up CT scan a few weeks later reported a 1-cm all round reduction of the mass. I-131 scan showed avid tracer uptake in the mass. This case suggests the possibility of this therapeutic option in nonthyroidal tumors that may concentrate radioiodine.

Radioiodine uptake by metastatic nonthyroidal adenocarcinoma of the lung in a patient with papillary thyroid carcinoma

A 49-year-old woman with a history of a hysterectomy for carcinoma of the cervix and papillary thyroid carcinoma showed multiple pulmonary metastases on chest radiography. An I-131 scan revealed multiple areas of increased uptake in the chest. These lesions were found to be metastatic cervical adenocarcinoma. The radioiodine uptake by the metastatic cervical adenocarcinoma of the lungs occurred in the presence of normal thyroid imaging in a patient with a thyroid nodule and papillary thyroid carcinoma.

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.

False positive 131I whole body scans in thyroid cancer

Well differentiated thyroid cancer is a rare disease in the UK. It is the only cancer which, having metastasized, remains curable by radioisotope therapy with 131I. The main indication for administering repeat doses of 131I is the appearance of abnormal uptake in a whole body scan following diagnostic or therapeutic 131I administration. False positive scans, showing the presence of 131I uptake in the absence of residual thyroid tissue or metastases can occur, although they are uncommon. Unless recognized as a false positive, 131I uptake may result in diagnostic error and lead to administration of an unnecessary therapy dose. We describe a series of nine patients in whom the scans showed false positive uptake of 131I, including cases where the cause of the uptake is still uncertain. We demonstrate the common sites of false positive uptake, discuss the underlying mechanisms and suggest a systematic approach to the interpretation of whole body scans in order to prevent unnecessary treatment with 131I.

Artifacts, anatomical and physiological variants, and unrelated diseases that might cause false-positive whole-body 131-I scans in patients with thyroid cancer

The whole body 131-I scan remains an important component in the postoperative treatment of patients with well-differentiated thyroid cancer. Because normal thyroid tissue remnants and residual or metastatic foci of well-differentiated thyroid cancer have the unique ability to concentrate, organify, and store 131-I, the whole body scan provides a depiction of those tissues that can be ablated with therapeutic doses of 131-I. Over time, it has become obvious that the whole body scan may also reveal foci of 131-i uptake owing to a wide variety of other causes. We provide a detailed pathophysiological classification of the artifacts, anatomic and physiological variants, and nonthyroidal diseases that may give rise to false-positive whole body scans in postoperative patients with thyroid cancer. These include ectopic foci of normal thyroid tissue; nonthyroidal physiological sites (eg, choroid plexus, salivary glands, gastric mucosa, urinary tract); contamination by physiological sections; ectopic gastric mucosa; other gastrointestinal abnormalities; urinary tract abnormalities; mammary abnormalities; serous cavities and cysts; inflammation and infection; nonthyroidal neoplasms; and currently unexplained causes. This article also provides a detailed review of the widely scattered English language literature in which these phenomena were originally described.

Inflammatory diseases of the lung causing false-positive 131iodine whole body scans in the evaluation of papillary thyroid carcinoma. Two case reports

The 131I whole body scan is commonly used to establish the presence of metastatic disease in papillary thyroid carcinoma. False-positive scans are rare, but have been reported. We present two cases of aberrant uptake of radioiodine after thyroidectomy and 131I ablation due to inflammatory conditions of the lung, aspergilloma, and respiratory bronchiolitis.

Radiographic and scintigraphic evidence of focal pulmonary neoplasia in three cats with hyperthyroidism: diagnostic and therapeutic considerations

Three cats were diagnosed as hyperthyroid based on clinical signs, historical findings, laboratory abnormalities, and basal serum thyroxine (T4) concentrations, and/or nuclear thyroid scans. Additionally, a presumptive diagnosis of thyroid carcinoma with pulmonary metastasis was made in each cat based on radiographic or scintigraphic evaluation. All three cats had solitary pulmonary nodules 1.5 to 2 cm in diameter on survey thoracic radiographs; one cat also had chylous pleural effusion and pulmonary lobar consolidation. Focal pulmonary accumulation of sodium pertechnetate (99mTcO4-) and/or radioiodine (131I) corresponding to radiographic lesions were seen in all cats. Two cats were treated with single ablative doses (1111 to 1480 MBq) of 131I; the remaining cat was euthanatized. One of the treated cats died 8 days later; the other cat was euthanatized 22 weeks following treatment. Histopathologic examination of tissue obtained at necropsy confirmed metastatic thyroid carcinoma in one cat and bronchogenic adenocarcinoma in two cats. Our findings indicate that increased radionuclide uptake in focal pulmonary lesions and cytologic evaluation of tissue obtained by fine-needle aspiration are not specific for thyroid tissue.

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.

False positive 131I total body scan due to an ectasia of the common carotidis

A cervical accumulation of radioiodine at Total Body Scan (TBS) in a patient who had been thyroidectomized for a follicular thyroid carcinoma led to unnecessary radioiodine treatment. Thyroglobulin measurements indicated constantly low levels. Following ultrasound scanning of the neck, echo-doppler examination of the cervical vessels and angiography with 99Tc, this area of increased activity at TBS imaging was shown to be due to an ectasia of the right common carotidis causing blood stasis and reverse flow.

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.

Misinterpretation of iodine uptake in papillary thyroid carcinoma and primary lung adenocarcinoma

This is the first case report of an iodine-storing metastasising carcinoma of extrathyroidal origin and the simultaneous presence of a papillary thyroid carcinoma. In the course of the disease, an increase in pathological iodine uptake was observed after repeated iodine-131 ablation, so that the original tentative diagnosis of a metastasising, differentiated thyroid carcinoma appeared to be confirmed; moreover, the histological work-up of a femur metastasis--without adequate immunohistochemical assessment--was misinterpreted. What is also remarkable about this case report is a pathological iodine-131 uptake both in the extrathyroidal primary tumor and the metastases.