False-positive Iodine-131 whole-body scan findings in patients with differentiated thyroid carcinoma: Report of 11 cases and review of the literature

Unusual Achalasia Presentation Detected on 131 I SPECT/CT in a Papillary Thyroid Carcinoma Patient

ABSTRACT

Various factors leading to unexpected false-positive 131 I uptake have been extensively studied in patients with differentiated thyroid carcinoma. In this case, we present a patient who underwent achalasia surgery and subsequently exhibited abnormal 131 I uptake on SPECT/CT imaging. The patient was a known case of papillary thyroid carcinoma that suggested to 131 I therapy. 131 I SPECT/CT showed linear increased activity in the distended esophagus.

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.

Factors Associated With Radioactive Iodine Therapy-Acquired Nasolacrimal Duct Obstruction

OBJECTIVE

To identify factors associated with radioactive iodine (RAI)-acquired nasolacrimal duct obstruction (NLDO).

METHODS

Retrospective chart review and telephone surveys of patients who received RAI therapy for thyroid carcinoma at an academic institution were conducted. Telephone surveys were used to screen for post-RAI NLDO diagnoses. Databases were reviewed for documented NLDO, demographics, RAI dose, total number of RAI treatments, and sialadenitis. Routine post-RAI whole-body scintigraphy (WBS) images were analyzed for the presence or absence of ¹³¹I sodium iodide (I-131) in the nasolacrimal duct. Intranasal I-131 activity was graded as none, low, moderate, and high; those with moderate or high activity were considered to have "increased" activity. Logistic and ordinal logistic regression models were used to evaluate the associations with NLDO while adjusting for I-131 dose.

RESULTS

Of the 209 patients who completed the survey, 15 (7%) had NLDO diagnoses. Increased intranasal I-131 activity on WBS, presence of nasolacrimal I-131 WBS activity, presence of documented post-RAI sialadenitis, and history of >1 RAI treatment were associated with the development of NLDO from univariate analyses (P ≤ .013). After adjusting for the administered dose of I-131, the presence of sialadenitis and nasolacrimal I-131 activity on WBS were the remaining 2 factors significantly associated with NLDO development (P < .001 and P = .01, respectively).

CONCLUSIONS

The presence of sialadenitis and nasolacrimal I-131 activity on WBS are I-131 dose-independent correlative factors for RAI-associated NLDO. Patients with these characteristics should be counseled on their increased risk of NLDO after RAI therapy for thyroid carcinoma.

Clinical Efficacy of Levothyroxine Sodium plus I 131 in the Treatment of Patients with Thyroidectomy and Its Effect on the Levels of Thyroglobulin and Thyrotropin

Objective

This study was to evaluate the clinical efficacy of levothyroxine sodium tablets combined with I 131 in the treatment of patients after thyroidectomy and the effect on thyroglobulin (Tg) and thyroid stimulating hormone (TSH) levels.

Methods

80 patients with differentiated thyroid cancer who required thyroidectomy after surgery between July 2019 and January 2021 were recruited for prospective study, 40 patients in the control group received levothyroxine sodium tablets, and 40 patients in the experimental group received levothyroxine sodium treatment plus I 131 treatment. Treatment effect, serum Tg and TSH levels, and relapse were measured.

Results

The removal rate of residual thyroid tissue in the experimental group (87.50%) was significantly higher than that in the control group (57.50%) (P < 0.05). Levothyroxine sodium tablets plus I 131 was associated with a significantly higher efficacy versus levothyroxine sodium tablets (P < 0.05). There were no significant differences in the serum Tg levels between the two groups before treatment (P > 0.05). After treatment, the serum Tg levels in both groups were significantly decreased, and levothyroxine sodium tablets plus I 131 resulted in a significantly lower Tg level versus levothyroxine sodium tablets (P < 0.05). Before treatment, the two groups showed similar TSH levels (P > 0.05). After treatment, patients receiving levothyroxine sodium tablets plus I 131 had a significantly greater increase in the TSH levels versus levothyroxine sodium tablets (P < 0.05). The recurrence rate of the experimental group was lower than that of the control group (P < 0.05).

Conclusion

Levothyroxine sodium tablets plus I 131 for post-operative patients with differentiated thyroid cancer enhance the removal rate of residual thyroid tissue, effectively reduce serum Tg level, and increase TSH level, with significant therapeutic effects, low recurrence rates, and a high safety profile.

Posttraumatic Scab on 131I Whole-Body Scan-A False-Positive Finding

ABSTRACT

131I scan plays a crucial role in the management of patients with differentiated thyroid cancer for the evaluation of remnant thyroid tissue, residual/recurrent metastatic disease, posttherapy tracer distribution, and response assessment to high-dose 131I therapy. Different causes secondary to physiological, pathological, and anatomical variations have been described for false-positive findings in the whole-body planar images. This case report of a patient of differentiated thyroid cancer with undocumented trauma to the left knee region a day before receiving the high-dose radioiodine therapy showed an interesting image finding of tracer uptake at unusual site in the posttherapy whole-body 131I scan.

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.

Pitfall of I-131 whole body scan: a mucinous adenocarcinoma of the ovary

False positive radioiodine uptake following thyroidectomy for differentiated thyroid cancer has been reported in some cases. A 57-year-old female patient was referred for ablative radioiodine treatment four weeks after undergoing total thyroidectomy for papillary thyroid carcinoma. Posttherapeutic I-131 scintigraphy showed uptake in the neck and large focus in the lower abdomen and pelvis. Pathology revealed a mucinous adenocarcinoma of the right ovary.

Pleuropericardial Cyst Mimicking a Metastasis of Differentiated Thyroid Carcinoma on Whole-Body Iodine-131 Scan: a Case Report

Post-therapeutic whole-body scan (WBS) with I-131 has been widely used for the follow-up of patients with well-differentiated thyroid cancer (DTC). Although the sensitivity of WBS with I-131 in detection of functioning thyroid tissues is high, its specificity is low. So, a further evaluation is required in cases of unexpected findings. The purpose of the study was to demonstrate that awareness of the potential pitfalls of WBS in DTC, knowledge of physiology and characteristics of radioiodine uptake, and correlation with other imaging modalities are needed to avoid incorrect management of patients with DTC. This is a case report of a 49-year-old woman with an unexpected area of increased I-131 uptake in the posterior lower chest, which was finally diagnosed as a pleuropericardial cyst. Due to the false-positive uptake of I-131 in the chest, an accurate interpretation of the scintigraphic findings should be made.

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.

Iodine-131 Therapy and Lacrimal Drainage System Toxicity: Nasal Localization Studies Using Whole Body Nuclear Scintigraphy and SPECT-CT

PURPOSE

The objective of this study was to evaluate the influence of dose on nasal localization of radioactive iodine-131 (I-131) following therapy for differentiated thyroid carcinomas.

METHODS

Retrospective evaluation of all patients who underwent post-therapy I-131 whole body scintigraphy and single photon emission computed tomography was performed. Patients were divided into 2 groups; group A were treated with 100 millicurie (mCi) and group B with ≥150 mCi. Databases were reviewed for demographics, diagnosis, and administered dosage of I-131. Whole body scintigraphy images were retrieved and nasal uptake was analyzed and classified as nil to trace, low, moderate, and high uptake and corresponding single photon emission CTs were analyzed for radioactive nasal activity.

RESULTS

A total of 100 patients were studied, 50 in each of the groups. The M:F ratio was 1.1:1 (27:23) in group A and 1.5:1 (30:20) in group B. The mean age was 43.12 years and 54.6 years in groups A and B, respectively. Papillary carcinoma of the thyroid was the most common type accounting for 82% (41/50) of patients in group A and 62% (31/50) in group B. Imaging studies revealed nil to trace nasal activity in 80% (40/50) in group A as compared with 56% (28/50) in group B. None of the patients in group A showed high nasal uptake, whereas 4% (2/50) in group B demonstrated such high activity.

CONCLUSION

Intranasal localization of radioactive I-131 was significant in patients receiving a dose of ≥150 mCi. Intranasal localization may partly explain toxicity to nasolacrimal duct and may be a risk factor for subsequent development of nasolacrimal duct obstructions.

Intrathoracic stomach mimicking bone metastasis from thyroid cancer in whole-body iodine-131 scan diagnosed by SPECT/CT

The whole-body iodine-131 scintigraphy is an imaging technique in monitoring patients with a history of thyroid cancer. Although the rate of false positives is negligible, it is not nonexistent. We report the case of an intervened and treated patient for thyroid cancer with good clinical and biochemical response. Scintigraphic findings were consistent with unsuspected bone metastasis. Fused SPECT/CT data allowed accurate diagnosis of giant diaphragmatic hernia associated with intrathoracic stomach, a very rare pathology that can lead to false positive results.

Variants and pitfalls on radioiodine scans in pediatric patients with differentiated thyroid carcinoma

BACKGROUND

Potentially false-positive findings on radioiodine scans in children with differentiated thyroid carcinoma can mimic functioning thyroid tissue and functioning thyroid carcinomatous tissue. Such false-positive findings comprise variants and pitfalls that can vary slightly in children as compared with adults.

OBJECTIVE

To determine the patterns and frequency of these potential false-positive findings on radioiodine scans in children with differentiated thyroid carcinoma.

MATERIALS AND METHODS

We reviewed a total of 223 radioiodine scans from 53 pediatric patients (mean age 13.3 years, 37 girls) with differentiated thyroid carcinoma. Focal or regional activity that likely did not represent functioning thyroid tissue or functioning thyroid carcinomatous tissue were categorized as variants or pitfalls. The final diagnosis was confirmed by reviewing the concurrent and follow-up clinical data, correlative ultrasonography, CT scanning, serum thyroglobulin and antithyroglobulin antibody levels. We calculated the frequency of these variants and pitfalls from diagnostic and post-therapy radioiodine scans.

RESULTS

The most common variant on the radioiodine scans was the thymic activity (24/223, 10.8%) followed by the cardiac activity (8/223, 3.6%). Salivary contamination and star artifact, caused by prominent thyroid remnant, were the most important observed pitfalls.

CONCLUSION

Variants and pitfalls that mimic functioning thyroid tissue or functioning thyroid carcinomatous tissue on radioiodine scan in children with differentiated thyroid carcinoma are not infrequent, but they decrease in frequency on successive radioiodine scans. Potential false-positive findings can be minimized with proper knowledge of the common variants and pitfalls in children and correlation with clinical, laboratory and imaging data.

F-18 Sodium Fluoride Positron Emission Tomography/Computed Tomography for Detection of Thyroid Cancer Bone Metastasis Compared with Bone Scintigraphy

Objective

The aim of the study was to compare the diagnostic performances of F-18 sodium fluoride positron emission tomography/computed tomography (bone PET/CT) and bone scintigraphy (BS) for the detection of thyroid cancer bone metastasis.

Materials and Methods

We retrospectively enrolled 6 thyroid cancer patients (age = 44.7 ± 9.8 years, M:F = 1:5, papillary:follicular = 2:4) with suspected bone metastatic lesions in the whole body iodine scintigraphy or BS, who subsequently underwent bone PET/CT. Pathologic diagnosis was conducted for 4 lesions of 4 patients.

Results

Of the 17 suspected bone lesions, 10 were metastatic and 7 benign. Compared to BS, bone PET/CT exhibited superior sensitivity (10/10 = 100% vs. 2/10 = 20%, p = 0.008), and accuracy (14/17 = 82.4% vs. 7/17 = 41.2%, p < 0.025). The specificity (4/7 = 57.1%) of bone PET/CT was not significantly different from that of BS (5/7 = 71.4%, p > 0.05).

Conclusion

Bone PET/CT may be more sensitive and accurate than BS for the detection of thyroid cancer bone metastasis.

Nonspecific iodine accumulation in surgical suture material mimicking follicular thyroid cancer bone metastasis in (131)I scintigraphy

A 23-year-old man with follicular thyroid carcinoma and cervical lymph node metastases showed a clear I focus on the skull after radioiodine therapy; therefore, an osseous metastasis was suspected. I and MRI fusion suggested the I focus to be adjacent to an epicranial suture from an early childhood trepanation for epidural hematoma. Radio-guided surgery found dark brown material to be the source of the radiation and successfully removed the material. Subsequent electron microscopy revealed a thread within the dark brown material, suggesting suture material as the cause of I accumulation.