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Hypofunctioning nodules on scintiscan using Tc-99m Pertechnetate or I-123 have a higher probability of malignancy compared to eu- or hyperfunctioning nodules. However, in the preoperative assessment of thyroid nodules, ultrasonography and ultrasonography guided fine needle aspiration biopsy play the most important role, especially for papillary thyroid cancer. The problem of differentiating follicular adenoma from highly differentiated follicular carcinoma however remains. Also the additional use of a multi tracer imaging strategy (Tl-201/Tc-99m subtraction scan, Tc-99m Sestamibi, Tc-99m Tetrofosmin dual phase scintigraphy) has not solved this problem. Although it is unlikely, the question whether FDG PET is able to give a better differentiation between benign and malignant tumours in the preoperative assessment of thyroid nodules is not answered up to now. In contrast to preoperative diagnostics, FDG PET is of great value in the postoperative follow up of differentiated thyroid cancer. In case of elevated serum thyroglobulin but negative I-131 WBS FDG PET is the method of choice to detect I-131 negative recurrences and metastases. FDG uptake in metastases from differentiated thyroid cancer is correlated to low differentiation and maybe bad prognosis. There is also evidence that FDG PET may have a role in the follow up of anaplastic and especially in medullary thyroid cancer in the future.

Rationale and Objectives: Scintigraphy is routinely used in evaluating thyroid nodules. Functioning nodules are reported to have a low probability of being malignant. Therefore cancer should appear hypo-functioning or "cold" on scintiscan. The aim of the study was to compare the scintigraphic pattern in different tumor stages of thyroid carcinoma. In addition, sonographic results are evaluated. In 151 patients with thyroid carcinoma 99mTc-pertechnetate scans were evaluated retrospectively by a visual inspection scoring method (A = no significant uptake to D = nodular uptake superior to normal thyroid tissue). Planar images were taken using a small field thyroid gamma camera. There were 52 patients with pT1 carcinoma (2 x follicular and 50 x papillary). The mean tumor size was 0.56 +/- 0.26 cm. The scintigraphic results were A and B in 5.7% (n = 6), C in 73% (n = 38), D in 15.6% (n = 8). Out of 40 patients with pT2 carcinoma, 34 had a papillary, 6 a follicular histology. Mean tumor size was 1.66 +/- 0.49 cm. The scintiscan was A in 12.5% (n = 5), B in 32.5% (n = 13), C in 42.5% (n = 17) and D in 12.5% (n = 5). There were 11 patients with pT3 carcinoma (4 x papillary, 7 x follicular). The mean tumor size was 3.96 +/- 0.88 cm in diameter. Scintiscan was A in 72.7% (n = 8), C in 27.3% (n = 3). Among 48 patients with pT4 carcinoma (2 x follicular, 1 x nondifferentiated, 45 x papillary), scan was A in 41.6% (n = 20), B in 14.5% (n = 7), C in 33.3% (n = 16) and D in 10.4% (n = 5). Mean tumor size was 2.16 +/- 1.45 cm (7 carcinomas < or = 1 cm, 23 x 1-2 cm, the remaining > 2 cm). Tumor size plays an important role in routinely used planar scintigraphy. Nodules greater than 2 cm in diameter tend to appear cold but microcarcinomas (< or = 1 cm) are often indifferent on scan. Therefore, planar 99mTc-pertechnetate scintigraphy is of little value in evaluating small thyroid nodules. In order to diagnose small thyroid nodules, ultrasonography and ultrasonographically guided FNAB should be recommended as the initial diagnostic steps in clinical routine.

The aim was to compare two thyroglobulin-immunoradiometric assays (Tg-IRMA) in the follow-up of patients with differentiated thyroid carcinoma (DTC) in order to set up interassay correlation, correlation to clinical background, and to determine whether a lower functional sensitivity (kit A: 0.5 ng/mL, kit B: 0.3 ng/mL) would allow an earlier detection of recurrences. Three hundred eight samples from 181 patients with DTC were investigated. The clinical interpretation of the Tg-IRMA results was based on comprehensive imaging and the clinical history before and during the study period. Groups were formed against this background and against the thyrotropin (TSH) levels of the samples (LT4- on and LT4-off). During a follow-up period that lasted until September 1998, the clinical situation was reevaluated in order to determine any changes in the patients' clinical status. The two assays presented a good interassay correlation of 0.838. Both assays had a high and comparably good sensitivity in the detection of recurrence of malignancy or distant metastases. Patients in remission had, in most cases, nonmeasurable or Tg values below 1 ng/mL. Kit B presented slightly measurable Tg results in a larger number of patients in remission; however, during the follow-up most of these slightly measurable Tg results were not reproducible, thus being most likely artifacts. Consequently, the functional sensitivity of 0.3 ng/mL of kit B showed no advantages in terms of an earlier tumor detection and seems to be unacceptably low. Negative consequences may be an increase in the number of investigations during the follow-up, which may be disconcerting for both the clinicians and the patients.

In the follow up of differentiated thyroid carcinoma (DTC) several scintigraphic methods are used in addition to the serum thyroglobulin and ultrasonography of the neck. Iodine-131 whole body scintigraphy (WBS), which is performed since many years, is able to detect iodine positive recurrence, lymph node metastases and distant metastases in a very specific way. However, the problem of I-131 WBS is the fact that only 67% of metastases from DTC accumulate iodine. Therefore non specific radionuclides like TI-201 or tracers such as Tc-99m Sestamibi or Tc-99m Tetrofosmin and new metabolic tracers like F-18 FDG were introduced in the diagnostic work up to detect iodine negative metastases as well. This study describes the comparison of different tracers in 35 patients with elevated thyroglobulin and suspicion of metastatic disease or already known metastases from DTC.

Unlabelled: Determination of thyroglobulin (Tg) levels, determined under endogenous thyroid-stimulating hormone stimulation after withdrawal of L-thyroxin treatment (off-T4), has been proven to be the most sensitive method for evaluation of patients with recurrent malignancy or distant metastases. This study uses a comparative approach between low-dose 131I scan and the previously reported highly sensitive 99mTc-tetrofosmin whole-body scintigraphy, using Tg-off-T4 as a basis for comparison., Methods: Fifty-eight consecutive patients of our follow-up program with primary thyroid carcinoma ablated with thyroidectomy and radioiodine therapy were examined after L-thyroxin withdrawal over 3-4 wk with 131I (185 MBq) and 99mTc-tetrofosmin whole-body scintigraphy and Tg determination (off-T4) within 5 days. Patients with Tg levels above 0.5 ng/ml were defined as Group A (n = 29). Group B (n = 29) comprised patients who had Tg levels (off-T4) below 0.5 ng/ml., Results: Iodine-131 revealed only 19 of 44 tumor sites (43.18%). Additionally, three remnants could be demonstrated. Sensitivity showed decreasing values for local recurrences (4 of 7, 57.1%), bone lesions (7 of 13, 53.85%) and mediastinal (2 of 4, 50%), lung parenchymal (3 of 7, 42.85%) and lymph node (2 of 9, 22.2%) metastases. Whole-body scintigraphy with 99mTc-tetrofosmin revealed a total of 39 of 44 malignant lesions (88.6%). Sensitivity was superior for lung parenchymal metastases (9 of 9, 100%), mediastinum (4 of 4, 100%) and lymph nodes (9 of 10, 90%) and inferior for bone metastases (11 of 13, 84.6%). Local recurrences could be detected in 6 of 7 patients (85.7%), and thyroid remnants were detected in 2 cases (2 of 11, 18.2%). One liver metastasis could not be detected because of the physiologic tracer distribution of 99mTc-tetrofosmin. Thyroglobulin-off-T4 detected malignant recurrence or metastases in 18 of 19 patients (94.7%) when a cutoff of 3 ng/ml was used and in 16 of 19 patients (84.2%) when a cutoff of 10 ng/ml was used. Specificity was calculated as 71.8% when a cutoff of 0.5 ng/ml was used, 89.7% when a cutoff of 3 ng/ml was used and 100% when a cutoff of 10 ng/ml was used., Conclusion: Scintigraphy with 99mTc-tetrofosmin showed clear advantages concerning sensitivity in most metastatic lesions when compared with low-dose 131I scan. Despite a slight lower specificity, 99mTc-tetrofosmin whole-body scintigraphy has, therefore, been proven to be a useful tool in the assessment of metastatic lesions in differentiated thyroid carcinoma.

We report a case of a 48-yr-old woman who underwent surgery because of papillary oxyphilic thyroid carcinoma pT3. After total thyroidectomy, we administered 2960 MBq (131)I for ablation of the residual tissue. initial follow-up visits showed no clinical, radiological or scintigraphic evidence of residual or metastatic thyroid tissue. Serum thyroglobulin levels (Tg) and (131)I whole-body scintigraphy were negative. Three years after thyroidectomy, the patient experienced seizures, and as a consequence a brain tumor was removed. It was an undetected metastasis of the primary thyroid carcinoma. Histological examinations showed that neither the primary tumor nor the metastasis produced any Tg. With this fact in mind and the knowledge of negative (131)I whole-body scans we had to concentrate on radiological (CT and MRI scans) and nonspecific scintigraphic methods such as 201TI whole-body scintigraphy in our management of the patient. Further follow-up demonstrated multiple metastasis by 201TI whole-body scan (mediastinum, bones and soft tissue), and most of them have been removed by surgery. This case report demonstrates that, in addition to (131)I whole-body scans and measurement of serum Tg, the use of nonspecific tracers like 201TI is important to detect (131)I and/or Tg negative metastases.