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

False-Positive Radioiodine Uptake From an Intracranial Surgical Clip

ABSTRACT

A 73-year-old man with papillary thyroid cancer underwent total thyroidectomy and bilateral neck dissections. He was subsequently treated with 131I. The posttherapy scan showed radioiodine uptake at the left supraorbital region, which localized to a metallic surgical clip. There was no evidence of metastasis in this area. This is not a commonly reported finding. Knowledge of this false-positive finding can help avoid unnecessary workup and treatment.

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.

Incidentally Visualization of the Thymus on Whole-Body Iodine Scintigraphy: Report of 2 Cases and Review of the Latest Insights

Radioiodine uptake is not commonly seen by the thymus gland. On the contrary, the gland is slowly replaced by fat after puberty. Herein, we present 2 patients with papillary thyroid carcinoma, follicular variant, and cervical lymph node involvement. After total/near-total thyroidectomy, the patients received I for ablation therapy. On posttreatment radioiodine scintigraphy, mediastinal I uptake was noted that finally was histologically/anatomically diagnosed as thymus gland uptake. It should be borne in mind as a potential cause of false-positive whole-body I scintigraphy.

Unusual metastases from tall cell variant of papillary thyroid cancer

BACKGROUND

Tall cell variant (TCV) cancer is considered more aggressive than the classic variant of papillary thyroid cancer (PTC). Distant metastases are more common among this variant and affect survival. Little is known about the molecular pattern of this histotype.

METHODS

This is a report of 2 cases of unusual metastases from TCV, BRAF V600E-positive.

RESULTS

A 38-year-old woman developed subcutaneous metastases during short-term follow-up; at medium-term follow-up, the patient showed detectable stimulated serum thyroglobulin without disease evidence at imaging. A 33-year-old man presented incidental thymic metastases at time of surgical treatment; this is the first case of not ectopic thymic metastases from PTC.

CONCLUSION

TCV may present with unusual metastases already during early follow-up. The more aggressive behavior could be linked to the higher prevalence of BRAF point mutations, but only a long-term follow-up might clarify if this association could worsen the prognosis. Moreover, skin metastases have been predictive factors of worse outcome in our patients, but not thymic metastases.

Radioiodine concentration by the thymus in differentiated thyroid carcinoma: report of five cases

The radioactive iodine has been used with great value as a diagnostic and therapeutic method in patients with differentiated thyroid carcinoma previously submitted to total thyroidectomy. False-positive whole-body scans may occur due to misinterpretation of the physiologic distribution of the radioisotope or lack of knowledge on the existence of other pathologies that could eventually present radioiodine uptake. Thymic uptake is an uncommon cause of false-positive whole-body scan, and the mechanism through which it occurs is not completely understood. The present paper reports five cases of patients with differentiated thyroid cancer who presented a mediastinum uptake of radioiodine in a whole-body scan during follow-up. The patients had either histological or radiological confirmation of the presence of residual thymus gland. It is very important to know about the possibility of iodine uptake by the thymus in order to avoid unnecessary treatment, such as surgery or radioiodine therapy.

Intense 18-fluorodeoxyglucose uptake by the thymus on PET scan does not necessarily herald recurrence of thyroid carcinoma

This is the first report of intense fluorodeoxyglucose positron emission tomography (FDG-PET) uptake secondary to thymic hyperplasia during follow-up for thyroid carcinoma. A 36-yr-old woman underwent thyroidectomy for a papillary carcinoma measuring 4 cm in diameter. After two doses of radioiodine, thyroglobulin (Tg) remained detectable following recombinant human TSH (rhTSH) stimulation. A whole body scan (WBS) was negative. On computed tomography (CT) scan, a slightly lobulated thymus was visualized. PET scan showed intense thymic uptake. Following resection, anatomo-pathological analysis showed homogenous hyperplastic thymic gland without neoplastic cells. Two months later, under levothyroxin (L-T4) substitution, Tg was no longer detectable and PET scanning did not show any 18-FDG uptake. This observation suggests that thymic FDG uptake does not necessarily herald recurrence of thyroid carcinoma and must be interpreted with caution in such a setting. Other conditions associated with abnormal uptake by hyperplastic thymus must also be envisaged.

A novel case of false-positive I-131 whole-body scan in thyroid carcinoma caused by subdural hematoma

Iodine-131 whole-body scintigraphy has been used extensively to detect thyroid remnants as well as metastatic disease in thyroid carcinoma postthyroidectomy. Over the years, numerous causes of false-positive scans have been reported. The authors report a novel case of a false-positive result resulting from a subdural hematoma mimicking a skull or cerebral metastasis.

Implications of mediastinal uptake of131I with regard to surgery in patients with differentiated thyroid carcinoma

BACKGROUND

Findings of mediastinal uptake of 131I after surgical treatment for differentiated thyroid carcinoma (DTC) are common, especially in young patients. Given the frequency of false-positive findings, a protocol for diagnostic and therapeutic strategies would be useful. With the goal of accurately selecting management strategies, the authors analyzed their data and data found elsewhere in the literature for correlations with the incidence of mediastinal 131I uptake and with treatment for patients exhibiting such 131I uptake.

METHODS

All patients with DTC who were treated between 1978 and 2000 at Groningen University Hospital (Groningen, The Netherlands) and who received adjuvant 131I ablation therapy were included in the current analysis, which involved retrospective review of all relevant data.

RESULTS

Five hundred four patients with DTC initially underwent total thyroidectomy, with additional 131I ablation performed for 489 of these patients. In 48 of 489 patients (9.8%), 131I uptake was seen in the mediastinum on a posttreatment scan. Analysis of those 48 patients and of cases in the literature demonstrated that serum thyroglobulin levels, risk status, and the presence of thymus on radiologic images were important in the surgical decision-making process.

CONCLUSIONS

Mediastinal uptake of 131I on posttreatment scans was found in approximately 10% of patients after total thyroidectomy for DTC. Based on the current data and the data presented in the literature, the authors developed a flow chart for determining appropriate treatment strategies, which included mediastinal dissection for high-risk patients and for patients with serum thyroglobulin levels > 10 ng/mL.

Thymic uptake of radiopharmaceuticals

The thymus, as the site of T-cell differentiation, plays a critical role in the development of the immune system. The gland increases in weight until puberty and then is slowly replaced by fat. Various radiopharmaceuticals can localize to the thymus before it involutes. This pictorial presentation reviews the appearance and proposed mechanisms of thymic uptake of Ga-67 citrate, F-18 fluorodeoxyglucose, radioiodine, and In-111 pentetreotide.

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.

Differentiation between healthy thyroid remnants and tumor tissue after radioiodine therapy in patients with differentiated thyroid carcinoma using in vitro phosphorus-31 magnetic resonance spectroscopy

BACKGROUND

The growth and spread of many tumors are triggered by changes in cell membrane metabolism, which can lead to systemic alterations in levels of phospholipids. We sought to determine whether plasma levels of several phospholipids could differentiate between healthy remnants of thyroid tissue and residual tumor tissue or metastases in patients with thyroid carcinoma.

METHODS

We measured plasma phospholipid levels by phosphorus-31 magnetic resonance spectroscopy (31P-MRS) in blood samples from 30 patients with thyroid cancer who had been rendered hypothyroid in preparation for diagnostic or therapeutic administration of iodine-131. All patients had undergone total thyroidectomy. Iodine-131 whole-body scintigraphy and measurements of thyroglobulin values during up to 3 years of follow-up were used to distinguish patients in remission from those with only healthy thyroid remnants and those with tumor tissue or metastases.

RESULTS

Mean (+/- SD) levels of sphingomyelin (0.33 +/- 0.06 mmol/L vs. 0.46 +/- 0.03 mmol/L, P <0.0001) and phosphatidylcholine (1.34 +/- 0.19 mmol/L vs. 2.15 +/- 0.33 mmol/L, P <0.0001) were significantly lower in patients with metastatic thyroid cancer (n = 8) than in patients (n = 12) who were in remission. Patients with only remnants of thyroid tissue (n = 10) also had significantly lower phospholipid levels than did patients in remission, but significantly greater levels that did patients with tumor tissue or metastases.

CONCLUSION

These preliminary results suggest that 31P-MRS may be useful in helping to differentiate the presence of tumor tissue, remnants of thyroid tissue not requiring further treatment, and remission in patients with thyroid cancer.

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.

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.

Radioiodine uptake in the head and neck

OBJECTIVE

To report two cases of sinusitis-associated radioiodine uptake in patients with thyroid cancer and to review the reported causes of false-positive radioiodine uptake in the head and neck area.

METHODS

We present the radiologic findings in two patients who had undergone treatment for papillary thyroid cancer and discuss other settings in which radioiodine uptake suggested the presence of metastatic disease.

RESULTS

Radioiodine whole-body scans of two patients who had had thyroid cancer demonstrated uptake in the sphenoid and maxillary sinuses, respectively, mimicking bone or brain metastatic involvement. The thyroglobulin levels were low. Computed tomographic (CT) scanning disclosed mucosal swelling in the sinuses, consistent with sinusitis. The radioiodine uptake cleared on a follow-up scan in one case and was more localized than the CT findings in the other. Eighteen causes of false-positive radioiodine uptake in the head and neck area have been reported. On the basis of the mechanism of uptake, they can be classified into four categories: (1) physiologic uptake (ectopic thyroid tissue), (2) nonthyroidal pathologic conditions (dacryocystitis, sinusitis, sinus mucocele, sialadenitis, folliculitis, Warthin's tumor, parotid cyst, porencephaly, posttraumatic cerebromalacia, and inflammation due to dental disease or a nose ring), (3) internal retention (ectasia of the carotid artery and an artificial eye), and (4) external contamination by body secretions (sweat and nasal, tracheobronchial, lacrimal, and salivary secretions). The estimated prevalence of external contamination in the head and neck area on whole-body radioiodine scans is 0.3%.

CONCLUSION

Physicians should rule out the presence of radioiodine uptake by inflamed mucosa of the paranasal sinuses, as well as various other causes of false-positive radioiodine uptake, before metastatic thyroid cancer in the head and neck area is diagnosed.

False-positive result of a total-body scan caused by benign thyroidal tissue after I-131 ablation

This case report illustrates a false-positive result of an I-131 total-body scan caused by abnormal, noncancerous thyroid tissue. A 39-year-old woman underwent an open biopsy and thyroidectomy for a papillary thyroid carcinoma. She was treated by ablation with 150.8 mCi I-131. A follow-up total-body scan revealed a solitary focus of increased activity near the midline at the upper border of the larynx that was subsequently excised. Histologic analysis indicated a fragment of thyroid tissue with chronic inflammation, fibrosis, and squamous metaplasia. No evidence of thyroid carcinoma was present. Hypofunctioning or nonfunctioning residual tissue within the thyroglossal duct may have been suppressed under euthyroid conditions, protecting it from ablation. This tissue may have become stimulated by the high thyroid-stimulating hormone levels, accumulating I-131 and producing a false-positive result of the scan.

Benign oral disease as a cause of false-positive iodine-131 scans

Post-thyroidectomy I-131 whole-body scintigraphy is an important aspect in the management of patients with thyroid cancer. The scan is used to detect residual thyroid tissue and distant functioning metastases. Extrathyroid I-131 accumulation does not always denote metastatic disease, and several potential sources of false-positive I-131 scans have been identified. This report presents four cases of benign oral disease as a cause of false-positive I-131 uptake. Benign oral disease has not been documented previously as an important source of false-positive I-131 whole-body scans.