131I Whole-body Scan Research Articles

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

BackgroundIodine-131 (I-131) whole-body scan (WBS) plays an important role in the management of patients with differentiated thyroid carcinoma (DTC), to detect normal thyroid remnants and recurrent or metastatic disease. A focus of I-131 accumulation outside the thyroid bed and the areas of physiological uptake is strongly suggestive of a distant functioning metastasis. However, many false-positive I-131 WBS findings have been reported in the literature. Patient findingsWe describe a series of 11 personal cases of patients with DTC, collected from 1992 to 2011, in whom diagnostic or post-treatment WBS showed false-positive retention of I-131 in various locations. SummaryFalse-positive accumulations of I-131 on WBS may be classified according to the underlying pathophysiological mechanisms: external and internal contaminations by body secretions, ectopic normal thyroid and gastric tissues, inflammatory and infectious diseases, benign and malignant tumors, cysts and effusions of serous cavities, thymic uptake, and other non classified causes. ConclusionsClinicians must be aware of possible false-positive findings to avoid misinterpretations of the I-131 WBS, which could lead to inappropriate treatments.

Management and follow-up results of an incidental thyroid carcinoma in a young woman with ovarian teratoma

Thyroid cancer in ovarian teratoma is reported to be rare and experiences are limited. A 26-year-old woman had undergone bilateral cystectomy and omentectomy for bilateral cystic adnexial masses. Pathological examination showed 1.5 cm follicular variant papillary thyroid carcinoma on the basis of unilateral mature cystic teratoma. Increased CA-125 and CA19-9 levels decreased to normal reference ranges after surgery, but postoperative magnetic resonance imaging indicated multiple abdominal cystic loci. After total thyroidectomy, high dose I-131 was administered to ablate thyroid tissue. Thereafter, levothyroxine was started to achieve subclinical hyperthyroidism. No iodine uptake was detected in post-therapeutic whole body scan (WBS) other than thyroid bed. This finding supported that tumor did not show dissemination to abdomen. No uptake on the first-year evaluation with low-dose I-131 WBS suggested the complete ablation of the thyroid gland. It is recommended that thyroid carcinoma arising from ectopic thyroid tissue in a teratoma should be managed as thyroid carcinoma in thyroid. However, direct dissemination to contiguous regions in abdomen and hematogenous dissemination to distant organs should be in mind. Radical surgery including total abdominal hysterectomy, bilateral salphingo-oopherectomy, pelvic and paraaortic lymph node excision and thyroidectomy is recommended. Fertility preserving surgery may be the surgical procedure as in the present case.

131I whole-body scan or 18FDG PET/CT for patients with elevated thyroglobulin and negative ultrasound?

The aim of this review is to discuss the current role of iodine-131 (131I) whole-body scanning (WBS) and fluorine-18-fluorodeoxyglucose positron emission tomography (18FDG PET) or PET/computed tomography (PET/CT) in the restaging of differentiated thyroid cancer (DTC), prompted by increasing thyroglobulin serum levels in patients with negative neck ultrasound. Studies in the literature which compared these two imaging methods are discussed in depth. 18FDG PET or PET/CT and 131I WBS may provide complementary information useful for the restaging of DTC patients, and the combined use of these methods should thus be considered to identify recurrent/metastatic DTC patients after total thyroidectomy. The accuracy of 18FDG PET/CT seems to be superior to that of 131I WBS and SPECT/CT in high-risk DTC.

Incidental Detection of Clinically Nondiagnosed Inguinal Hernia in 131I Whole-Body Scan

I whole-body bone scan was performed for an adult male patient after postradioactive iodine ablation of thyroid carcinoma. Besides the small thyroid remnants in the neck region, an incidental detection of left inguinal hernia was made in the scan, which was later confirmed by clinical examination. Despite the large size of the hernia, the patient was unaware of the condition. It can be concluded that, similar to other imaging procedures, incidental detection of unrelated clinical problems is possible in I scan also, and such early diagnosis prevents further complications that the patient may develop in the future.

Follow-up value of the detection of thyroglobulin and whole body scan by ^131I for thyroid cancer after treatment by ^131I

Objective To explore the value of follow-up of serum TSH stimulating thyroglobulin (Tg) test and 131I whole body scan(WBS) in patients with differentiated thyroid cancer(DTC) who were treated by 131I.Methods By SPSS software,Kappa test was performed between results of serum Tg,TgAb test and WBS for diagnosis of persistent/recurrent DTC.Results Consistency test of TSH stimulating Tg,TgAb and 131I WBS for diagnostic persistent/recurrent or metastasis of DTC:kappa value =0.587,SE =0.076,P ＜ 0.01.Although the results showed that two measurements appeared definite consistency,it is dissatisfactory.Conclusion Serum TSH stimulating Tg test and 131I whole body scan(WBS) are important follow-up tools for patients with DTC.Because of Tg interfering it is necessary to performed TgAb test simultaneously,when Tg test was performed.Especially 131I WBS do is not absent because false negative would be able to appeared in single serum TSH stimulating Tg and TgAb test. Key words: Thyroid Neoplasms; Immuuoglobulius ; Thyroid-stiwulating; Iodine

Sustained and Diffuse 131I Avid Bone Metastases With Low Thyroglobulin Levels in a Patient With Papillary Thyroid Carcinoma

A 63-year-old man with papillary thyroid carcinoma (PTC) and bone metastases was treated with 131I residual thyroid ablation (RTA) and 2 repeated post-ablation 131I therapies after total thyroidectomy. 131I whole-body scans (WBS) demonstrated sustained and diffuse 131I avid bone metastases, accompanied by persistent very low thyroglobulin (Tg) levels and negative antithyroglobulin antibody (TgAb) in post-ablation 131I therapies in hypothyroid state after levothyroxine withdrawal. The spread of bone metastases were found on the last therapeutical 131I WBS. The benefit of 131I therapy after levothyroxine withdrawal should be weighed even if the metastases are 131I avid in poorly differentiated thyroid carcinoma.

Correlation of 18F-FDG PET/CT Findings With Histopathological Results in Differentiated Thyroid Cancer Patients Who Have Increased Thyroglobulin or Antithyroglobulin Antibody Levels and Negative 131I Whole-Body Scan Results

This study aimed to investigate the correlation of 18F-FDG PET/CT findings with histopathological results in defining the recurrence of the disease in patients with differentiated thyroid cancer (DTC) who have increased thyroglobuline (Tg) or anti-Tg antibody (TgAb) levels and negative 131I whole-body scan (WBS) result. A total of 59 patients with DTC (44 women, 15 men; mean [SD] age, 48.2 [22.6] years) were included in the study. All of the patients had previous papillary thyroid cancer, and all of them had undergone radioiodine ablation after a total or near-total thyroidectomy. After radioiodine ablation, patients were followed up for approximately 2.5 years. In the follow-up, the patients with negative 131I-WBS results and increased Tg or TgAb levels under thyroid-stimulating hormone-stimulated conditions underwent an 18F-FDG PET/CT scan to determine any recurrence of disease. There were negative or uncertain findings in the neck ultrasonography and/or thorax CT in most of the patients. The 18F-FDG PET/CT findings were compared with the histopathological results in all patients. Although 49 patients had increased Tg levels, the remaining 10 patients had increased TgAb levels. In patients with high Tg levels, 18F-FDG PET/CT scan results were negative in 10 and positive in 39 patients. In this patient group, 18F-FDG PET/CT findings were true positive, true negative, false positive, and false negative in 32, 3, 7, and 7 patients, respectively. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 18F-FDG PET/CT in this group were calculated as 82%, 30%, 80%, 30%, and 71%, separately. In the receiver operating characteristic analysis, a 4.5 cutoff SUV(max) was calculated with 75% sensitivity and 70% specificity for predicting disease recurrence. Cutoff Tg level was calculated as 20.7 ng/mL with 75% sensitivity and 55% specificity. In 10 patients with high TgAb levels, 18F-FDG PET/CT was true positive, true negative and false positive in 6, 2, and 2 patients, respectively. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 18F-FDG PET/CT in this patient group were calculated as 100%, 50%, 75%, 100%, and 80%, respectively. 18F-FDG PET/CT may be a useful imaging modality in defining recurrence of the disease in patients with DTC who have increased Tg or TgAb levels, negative 131I-WBS results, and negative or suspicious neck ultrasonography and/or thorax CT results. Although 18F-FDG PET/CT seems to be a more sensitive method in patients with increased TgAb levels, the number of patients is not enough to make a substantiated comment.

Empiric Therapy with Low-Dose I-131 in Differentiated Cancer Thyroid: What is the Magic Number?

Low dose radioactive iodine-131 (RAI) has been widely reported in the treatment of patients with differentiated thyroid cancer (DTC) since 1970's. However, the clinical outcomes, dosage of I-131 and criteria for successful ablation are different in various studies. The aim of this study was to assess clinical outcome 18-month after RAI therapy in selected DTC patients and identify factors associated with a good response. In this experimental study, among patients with DTC referred to the Nuclear Medicine Department and had an indication for RAI therapy in the period between December 2008 and January 2011, 108 subjects were selected randomly. The patients were randomly divided into three groups and empiric low dose therapy with 30, 50 or 75 mCi of I-131 was administered. Patients were monitored closely clinically and with serum thyroglobulin assays and I-131 whole-body scans at 6 monthly intervals for 18-month after treatment. Among 105 patients who completed follow-up, 86% were successfully ablated with a single low dose of I-131. There was no statistically significant difference in ablation rates in the subgroups receiving 30.50 or 75 mCi of I-131. Cumulative ablation rate was 99% in patients after the second dose of low dose therapy. If appropriate selection criteria are used in DTC, successful remnant ablation can be achieved with low doses of I-131 in the range of 30-75 mCi. No significant differences were found in results achieved with 30.50 or 75 mCi of I-131. As the majority of the DTC patients fall within the inclusion criteria of this study, they can be treated on an ambulatory basis with associated low cost, convenience, and low whole-body radiation-absorbed dose to the patients.

FDG PET/CT in the Detection of Metastases in a Patient With Tg and 131I WBS Negative Follicular Thyroid Cancer

After a total or near total thyroidectomy and radioiodine ablation therapy for differential thyroid cancer (DTC), routine follow-up methods are (131)I or (131)I whole-body scanning (WBS) as well as serum thyroglobulin (Tg) and anti-thyroglobulin (anti-Tg) levels. We describe a case of a 41-year-old woman with follicular thyroid cancer. Although serum Tg level and (131)I WBS were negative after radioiodine ablation therapy, she had pain around her left medial clavicle. FDG PET/CT was performed for any undetected metastases. FDG PET/CT showed hypermetabolic bone metastases in the left medial clavicle. Biopsy confirmed metastases of the thyroid follicular carcinoma.

Prognostic Significance of FDG PET/CT on the Follow-up of Patients of Differentiated Thyroid Carcinoma With Negative I131 Whole-Body Scan and Elevated Thyroglobulin Levels

Department of Nuclear Medicine Department Fondazione Poliambulanza Brescia, Italy [email protected] Conflicts of interest and sources of funding: none declared.

The Effects of the Factors Related to the Patient and the Disease on the Performance of Ablation Therapy in Patients with Differentiated Thyroid Cancer who have Received I-131 Ablation Therapy

Objective: To investigate whether the factors related to the patient and the disease have any effect on the success of ablation therapy in patients with differentiated thyroid cancer who have received I-131 ablation therapy.Material and Methods: All the patients with differentiated thyroid cancer were referred for I-131 ablation therapy after thyroidectomy between July 2007 and September 2009. The patients had at least six months of follow-up. Age, gender, type of tumor, presence of capsule invasion, size of tumor, number of the tumors, localization of the tumor, invasion of thyroid capsule, lymph/vessel invasion, presence of metastatic lymph nodes, type of surgery, preablation values of thyroglobulin (Tg), AntiTg, TSH, surveys for the evaluation of metastatic disease, (thyroid and bone scintigraphy, neck and abdominal ultrasonography, chest and brain computerized tomography), administered dose, postablation I-131 whole body scan (WBS) and diagnostic I-131 WBS, neck USG, values of Tg and AntiTg at the 6th month were recorded. The presence of residual thyroid activity on the 6th month diagnostic I-131 WBS image was accepted as the criterion for ablation success.Results: 191 patients with differentiated thyroid cancer were assessed in this study. The overall success rate of the first ablation therapy was 74.3%. The success rate of the ablation therapy was 66% and 75% in metastatic group and non-metastatic group, respectively. Except the significant correlation between the number of pathologic lymph nodes and the success of ablation (p=0.025), there was no other significant correlation between the patient/disease related factors and the success of ablation therapy.Conclusion: Significant correlation between the number of the pathologic lymph nodes and the ablation therapy performance can also be due to statistical error because of the limited sample size. There was no significant correlation between other patient/disease related prognostic factors and the success of ablation therapy.Conflict of interest:None declared.

Three Weeks Withdrawal of T4 Prior to I131 whole Body Scan Can Achieve the Required Serum TSH Level with Significantly Less Hypothyroidism

Introduction: I131 whole body scan (WBS) is used in follow–up of patients with well differentiated thyroid cancer (WDTC) post total thyroidectomy and I131 ablation therapy. Traditionally, it is performed after withdrawal of Thyroxine (T4) for at least 4-6 weeks to stimulate endogenous TSH to a level more than 30mIU/L. T4 withdrawal is associated with significant symptoms of hypothyroidism. In clinical practice, several studies report that serum TSH rapidly reaches the level of >30mIU/L at a mean of 17 to 18.1 days after T4 withdrawal in 96.2% of patients, reducing the duration of hypothyroidism and improving acceptance of scanning with I131 with minimal impact on health related quality of life (QOL).Aim of the study: The aim of the current study is to compare effects of T4 withdrawal for 3 weeks versus traditional withdrawal for 4 weeks on serum TSH level and hypothyroid symptoms in patients with WDTC presenting for I131 follow up WBS post total thyroidectomy and successful I131 ablation therapy.Patients and methods: One hundred patients with WDTC presented for I131 WBS post successful complete ablation of residual functioning thyroid tissue in the neck, all had suppressed or within normal TSH level. They were divided into 2 equal groups. Group I, instructed to withdraw Thyroxine for 3 weeks and group II, instructed to stop thyroxine for 4 weeks. Serum TSH level was estimated for all patients prior to oral intake of I131. Also, a questionnaire of main hypothyroid symptoms was filled by all patients about presence or absence of the symptoms and their severities that were divided into mild, moderate and severe.Results: For group I, 49 patients (98%) had TSH level >30 mIU/ml (mean=77.4±27.9), while all patients in group II (100%) achieved significantly higher TSH level (mean=119.1±42.1). There was a highly significant positive correlation (p<0.001) between number of symptoms and late serum TSH level within each group. The number of symptomatic patients was 39 patients (78%) in group I having a total number of 100 symptoms, with a mean of 2.0±1.5; out of them 60 mild, 29 moderate and 11 severe representing 60%, 29% and 11%, respectively. While for group II, number of polysymptomatic patients was 46(92%) with a total number of 233 symptoms with a mean of 4.7±2.6; out of them 70 mild, 95 moderate and 68 severe representing 30%, 40.8% and 29.2%, respectively. Patients in group I had significantly less hypothyroidism as regards number of patients, number of symptoms and their severity compared to group II. Moreover, a significant positive correlation between number of hypothyroid symptoms and serum TSH level was detected in both groups. Conclusion: It is concluded to withdraw thyroxine for 3 weeks instead of 4 weeks for patients with well differentiated thyroid carcinoma prior to regular follow up I131 WBS to achieve the desired serum TSH level with significantly less hypothyroid symptoms and better quality of life.

“Bulky Mass”

Poorly differentiated follicular thyroid carcinoma (PDFC) is a tumor of follicular cell origin with intermediate attributes between well-differentiated carcinomas and anaplastic carcinomas. The majority of patients presenting with distant metastases have locally advanced tumors, being lungs and bones the most common sites affected. We present a case of a patient with a painful bulky mass at the left thorax-abdominal wall as an uncommon distant metastasis of a PDFC. After thyroidectomy, a pre-ablative 131I whole-body scan showed distant metastases on the neck, both lungs, and lateral chest-abdominal wall, so the administration of I for thyroid remnant ablation stimulated with RH-TSH was decided.

Axillary Lymph Node Metastasis of Papillary Thyroid Carcinoma Detected by FDG PET/CT in a Thyroglobulin-Positive Patient With Negative Whole-Body 131I Scan

Axillary metastasis is not a common finding in papillary carcinoma. 18F-FDG can detect foci of metastasis in patients with negative 131I scan. We report a case of a 64-year-old man who had undergone thyroidectomy and 131I ablation due to classic type of papillary carcinoma 14 years ago. Follow-up examination revealed high serum thyroglobulin and negative whole body 131I scan. 18F-FDG PET/CT showed focally increased uptake in right axillary as well as supraclavicular and bilateral cervical lymph nodes. Histopathological examination of the surgically removed lymph nodes confirmed the metastasis of papillary thyroid carcinoma.

Prognostic Significance of FDG PET/CT on the Follow-Up of Patients of Differentiated Thyroid Carcinoma With Negative 131I Whole-Body Scan and Elevated Thyroglobulin Levels

This study aimed (a) to determine the clinical and histopathologic factors that are related to FDG avidity in the recurrence/metastases of patients with differentiated thyroid carcinoma (DTC) who present with elevated thyroglobulin (Tg) levels and negative 131I whole-body scans (WBSs), (b) to clarify Tg cutoff levels in this setting, and (c) to evaluate the impact of PET/CT on patient management strategies and hence to critically look into the importance of PET/CT in combination with Tg in clinical decision making. A total of 105 patients with DTC with negative 131I WBS and neck ultrasound but elevated Tg, who underwent FDG PET/CT for the suspicion of recurrent/metastatic disease, were included in this analysis. All patients had previously undergone total thyroidectomy and radioiodine ablation/therapy. PET/CT results were correlated with Tg levels and clinical and histopathologic characteristics of the primary tumor compared with the follow-up data. PET/CT was true-positive in 69 patients (of which 23 had surgically amenable disease), true-negative in 20, false-positive in 6 patients and false-negative in 10 patients. Extrathyroidal spread was an independent risk factor related to FDG-avid recurrence. Tumor size was significantly higher in PET-positive patients than others, 2.25 (1.8) versus 1.5 (1.1) cm, P = 0.02. Significant correlation was observed between PET positivity and high Tg levels (P = 0.0001). Receiver operating characteristic curve analysis demonstrated a Tg cutoff of 1.9 ng/mL under thyroid-stimulating hormone suppression, 38.2 ng/mL with thyroid-stimulating hormone stimulation. Among PET-negative patients, no recurrence was detected in patients with undetectable/suppressible Tg in on-therapy state. PET positivity correlated with extrathyroidal spread, and elevated Tg in recurrent/metastatic DTC. FDG PET/CT in combination with Tg levels was crucial in defining management strategies in patients with DTC with negative 131I WBS. A negative FDG PET/CT scan predicts a favorable prognosis and lack of recurrence on follow-up in patients with "suppressible Tg" levels in the on-therapy state despite significant elevation of Tg in the off-therapy state.

A randomized equivalence trial to determine the optimum dose of iodine-131 for remnant ablation in differentiated thyroid cancer

We conducted a stratified randomized equivalence/noninferiority trial from January 2001 to December 2006 to determine whether lower administered activities are as effective as 3.7 GBq (100 mCi) of iodine-131 (I) for remnant ablation. The sample size was found to be 450 on the basis of 80% power (α=5%) and noninferiority margin (δ=0.15). We used an allocation ratio of 2 : 2 : 1 for the 0.93, 1.85, and 3.7 GBq (25, 50, and 100 mCi) groups, respectively. Randomization with concealment was followed for patient group allocation. All patients underwent preablation I whole-body scan, 48-h radioiodine neck uptake measurements and post-therapeutic scans. The patients were advised suppressive L-thyroxine therapy (2 µg/kg/day). Repeat evaluation was performed after 6 months, along with thyroglobulin and antibody assays. The criteria for ablation were as follows: major criterion - negative I whole-body scan; minor criteria - 48-h radioiodine neck uptake less than or equal to 0.2% and stimulated thyroglobulin less than or equal to 10 ng/ml. A total of 422 patients who fulfilled the inclusion criteria (360 papillary and 62 follicular) could be recruited. As per AJCC, 6th ed., we had 70, 11, and 19% of patients in stage I, II, and III, respectively. First-dose ablation was 81.5, 84.9, 88.5, and 84.2% in the 0.93, 1.85, and 3.7 GBq groups and overall, respectively. Histology had no effect on ablation rate. The equivalence testing of the hypothesis was conducted between the 0.93 and 3.7 GBq groups, the 1.85 and 3.7 GBq groups, and the 0.93 and 1.85 GBq groups. Results showed that, at a significance level of 5%, the null hypothesis was rejected for each pair. First-dose I ablation rates at 6 months with 0.93, 1.85, and 3.7 GBq of I are equivalent with the prespecified clinically acceptable noninferiority margin. We conclude that we are probably administering too much I for remnant ablation (trial registration number: CTRI/002291).

L’apport de l’imagerie hybride TEMP/TDM dans la prise en charge du cancer différencié de la thyroïde

IntroductionSingle photon emission computed tomography combined with a low dose computed tomography (SPECT/CT), is a hybrid imaging integrating functional and anatomical data. The purpose of our study was to evaluate the contribution of the SPECT/CT over traditional planar imaging of patients with differentiated thyroid carcinoma (DTC). MethodsPost-therapy iodine 131 (131I) whole-body scan followed by cervico-thoracic SPECT/CT, were performed in 100 patients with DTC. ResultsAmong these 100 patients followed for a predominantly papillary DTC, planar imaging and SPECT/CT, were perfectly concordant in 70% of patients and discordant in the remaining 30%. The use of fusion imaging SPECT/CT compared to conventional planar imaging allowed us to correct our therapeutic approach in 27% (27/100 patients), according to the protocols of therapeutic management of our institute. ConclusionSPECT/CT is a hybrid imaging modality which provides better identification and more correct anatomic localization of the foci of radioiodine uptake with impact on therapeutic management.

Detection of Subcentimeter Metastatic Cervical Lymph Node by 18F-FDG PET/CT in Patients With Well-Differentiated Thyroid Carcinoma and High Serum Thyroglobulin But Negative 131I Whole-Body Scan

This study aimed to evaluate the diagnostic value of 18F-FDG PET/CT and identify the best parameter to detect subcentimeter cervical nodal metastasis in patients with a well-differentiated thyroid carcinoma (WDTC), elevated serum thyroglobulin (Tg) levels, but negative findings in the 131I whole-body scan (WBS). We prospectively studied 30 consecutive patients with WDTC after standard surgery and radioiodine treatment. All patients had serum Tg greater than 10 ng/mL during thyroid hormone withdrawal but negative findings in the therapeutic 131I WBS. One whole-body CT scan and serial whole-body and neck PET scans were performed between 10 and 170 minutes after 18F-FDG injection. Parameters studied were SUVmax, percent change in SUVmax, SUV ratios of lesions to reference organs, and their percent change. Result in the PET/CT scan was correlated with histopathology and follow-up information. Patient-based and lesion-based (subcentimeter cervical lymph nodes) analyses were performed. Outcome of Tg level after lymph node resection was also analyzed. The overall sensitivity, specificity, accuracy, and positive and negative predictive values were 100%, 78%, 93%, 91%, and 100%, respectively. In lesion-based analysis, the differential SUVmax between 2 time points did not provide higher sensitivity than the individual SUVmax at the 60th or 90th minute. A combined SUVmax at the 90th minute greater than 2.75 and a percent change of SUVmax between the 60th and 90th minute greater than -1.1% provides the best diagnostic value with sensitivity, specificity, accuracy, and positive and negative predictive values of 81%, 90%, 83%, 97%, and 56%, respectively. After surgery, patients with completely resected PET-positive nodes without distant metastasis showed reduction of suppressed Tg to less than 2 ng/mL. Combined SUVmax at the 90th minute and the percent change of SUVmax between the 60th and 90th minute provides the best diagnostic value to differentiate benign from malignant conditions in subcentimeter lymph nodes.

Role of 18F-FDG - PET/CT in Patients with Differentiated Thyroid Cancer Who Present with Elevated Thyroglobulin and Negative 131I Whole Body Scan

Aim of the work: To detect the ability of 18F-FDG with PET/CT to explain the elevated Tg levels in patients with negative 131I whole body diagnostic dose scan and to correlate of 18F-FDG with PET/CT with other diagnostic methods and histopathologic diagnosis.Patients and methods: 20 patients (13 males and 7 females) with pathologicall proven differentiated cancer thyroid were included in the study. All patients were subjected to near total thyroidectomy. 8 out of the 20 patients also underwent lymph node dissection. All received 131I ablation and had a negative whole body scan during follow up. They had unexplained elevated (> 10 ng/ml or more) or rising serum Tg levels (5-10ng/ml). All patients were subjected to full history, clinical examination, Laboratory and radiological assessment as well as 18F-FDG PET/CT study.Results: Neck US detected 7 lesions in 6 patients, all of them confirmed to be positive by PET/CT and an additional 13 neck lesions were detected by PET/CT in 15 patients. CT chest detected 8 patients, 6 of them confirmed by PET/CT while 2 lung lesions were negative. Eight additional mediastinal lymph node metastases were detected by PET/CT. PET/CT showed positive findings in 19/20 patients. In the remaining no cause for the elevated Tg was found with PET/CT or other radiological methods. PET/CT directed the management in 14/20 patients either to surgery or to external radiotherapy with normalization of Tg level within weeks after treatment.Conclusion: 18F-FDG PET/CT is of undeniable clinical value in patients with negative 131I whole-body scan results who are suspected of having a metastatic thyroid disease. It is able to detect significantly additional tumor sites than US or CT procedures.

Incidence and implications of negative serum thyroglobulin but positive I-131 whole-body scans in patients with well-differentiated thyroid cancer prepared with rhTSH or thyroid hormone withdrawal

To evaluate the incidence and clinical implications of a positive whole-body I-131 scan but negative stimulated serum Tg/TgAb level following an ablative or diagnostic I-131 dose in patients with well-differentiated thyroid cancer and whether there is a difference in incidence if prepared with thyroid hormone withdrawal compared with rhTSH stimulation. I-131 scan findings, serum Tg/TgAb levels, TNM stage and method of thyroid tissue stimulation in 193 consecutive patients (138F, 55M) with well-differentiated thyroid cancer undergoing postoperative ablative I-131 therapy and 121 consecutive (94F, 27M) patients undergoing diagnostic I-131 surveillance scans were retrospectively reviewed. Comparisons of proportions were performed using Chi-square tests. Clinical, biochemical and I-131 scan follow-up data were obtained for each patient cohort. 39/193 (20·2%) postablative I-131 and 10/121 (8·3%) diagnostic I-131 patients had negative stimulated serum Tg/TgAb levels but positive I-131 scans for residual thyroid tissue. Nine (4·7%) of the postablative patients had I-131 uptake in the lateral neck suspicious for loco-regional metastatic disease. In the postablative I-131 group, 38/169 (22·5%) prepared with rhTSH compared to 1/24 (4·2%) prepared with thyroid hormone withdrawal were Tg/TgAb negative but I-131 scan positive (P = 0·04). Follow-up of 21/39 postablative I-131 patients with negative Tg/TgAb but positive I-131 scans confirmed a significant proportion of patients (4/21) (19·1%), remained Tg/TgAb negative/I-131 scan positive, some of whom had higher-risk disease at original diagnosis (2/4) (50%). Our study confirms that in the setting of I-131 ablation therapy or diagnostic I-131 scanning, a significant proportion of patients (20·2% and 8·3%, respectively) have residual benign or malignant thyroid tissue on whole-body scanning despite a negative stimulated serum Tg level. Whether such patients who would otherwise be missed as having residual thyroid tissue on serum Tg testing alone have a worse clinical outcome remains uncertain. Our findings do however suggest performing both stimulated serum Tg/TgAb levels and I-131 scans for the follow-up of patients with higher-risk thyroid cancer may be important. There may also be a slightly higher incidence of this phenomenon in patients prepared with rhTSH rather than by thyroxine withdrawal.