This article is mentioned in:

Introduction

The incidence of follicular thyroid cancer is lower than that of papillary thyroid cancer in thyroid malignant tumors and is, therefore, the second most common thyroid malignancy (1). Follicular thyroid cancer is mainly characterized by a follicular structure. It is a differentiated thyroid cancer and demonstrates positive expression of the sodium-iodide symporter. Therefore, the tissues of follicular thyroid cancer generally uptake iodine, which is the biological basis for the detection of cancer lesions by 131I whole-body imaging and the treatment of follicular thyroid cancer by radioactive 131I (2,3). 99mTcO4− and the iodide ion have a number of similar features, so 99mTcO4− can also be absorbed by the thyorid (4). Follicular thyroid cancer may develop into regional nodal metastasis and may also progress into hematogenous metastasis (1). The accurate detection of recurrent and metastatic lesions of follicular thyroid cancer is significant in the staging of diseases and the evaluation of the therapeutic effect and prognosis (1). The present study describes a patient with follicular thyroid cancer whose metastatic lesions were detected using a 99mTcO4− whole-body scan. Informed consent was obtained from the patient prior to the study.

Case report

A 69-year-old female was admitted to Zhongnan Hospital of Wuhan University (Hubei, China) complaining of left stethalgia for three weeks. A physical examination revealed that the second rib in anterior left chest and the fourth thoracic vertebra were swollen and painful when palpated. The thyroid glands of the patient were intumescent and the left lobe to the isthmic portion was palpated as a hard and fixed nodule with an asperous surface, without pain. Laboratory examination demonstrated that the thyroid, liver and kidney functions, as well as the routine blood and urine test results, were all normal.

Thyroid imaging was performed at 10 min following the intravenous injection of Na99mTcO4 at 185 MBq. The result demonstrated a regional area of markedly decreased 99mTcO4− uptake with an irregular edge within the middle portion of the left lobe of the thyroid. A conglomerate area of increased 99mTcO4− uptake was identified in the left chest (Fig. 1). Subsequently, 99mTcO4− whole-body imaging was performed for the patient. The result revealed abnormal lesions of increased 99mTcO4− uptake in the left chest, thoracic vertebrae, lumbar vertebrae and left ilium (Fig. 2). The following day, whole-body bone imaging was performed at 3 h following an intravenous injection of 99mTc-methylene diphosphonate at 740 MBq. The imaging outcome demonstrated that the left anterior branch of the second rib, the fourth and twelfth thoracic vertebrae and the midpiece of the right thigh bone exhibited increased radioactive uptake. The third and fourth lumbar vertebrae and the left posterior inferior iliac spine were suspected of abnormal uptake, whereas the partial osseous tissue of the left anterior branch of the second rib demonstrated decreased radioactive uptake (Fig. 3).

Figure 1 Thyroid static imaging with 99mTcO4− showing a nodule in the middle portion of the left lobe of the thyroid with a decreased uptake and unclear edge, and an area of the left chest with a markedly increased uptake.

Figure 2 99mTcO4− whole-body imaging showing one site of the left chest, two sites of thoracic vertebrae, two sites of lumbar vertebrae and one site of the left ilium with an increased uptake.

Figure 3 Whole-body bone imaging showing the left anterior branch of the 2nd rib, the 4th and 12th thoracic vertebrae and the midpiece of the right thigh bone with an increased uptake of 99mTc-methylene diphosphonate. The 3rd and 4th lumbar vertebrae and the left posterior inferior iliac spine were suspected of abnormal uptake, whereas the partial osseous tissue of the 2nd rib presented with an osteolytic lesion.

A computed tomography (CT) scan of the thoracic region revealed a mass on the left thoracic wall, bony destruction of the left anterior branch of the second rib (Fig. 4) and the destruction of the crest of the fourth thoracic vertebra (Fig. 5). A magnetic resonance imaging (MRI) scan of the vertebrae and pelvic cavity demonstrated that the twelfth thoracic vertebra (Figs. 6 and 7), the pedicle of the fourth lumbar vertebral arch (Fig. 7) and the left ilium presented an abnormal signal (Fig. 8).

Figure 4 Computed tomography with contrast showing the 2nd rib with bony destruction and a markedly enhanced mass.

Figure 5 Computed tomography with contrast showing the 4th thoracic vertebra with bony destruction, and an enhanced lesion.

Figure 6 Magnetic resonance imaging showing the 12th thoracic vertebra with bony destruction.

Figure 7 Magnetic resonance imaging showing the 12th thoracic vertebra and the pedicle of the 4th lumbar vertebral arch with an abnormal signal.

Figure 8 Magnetic resonance imaging showing the left ilium with an abnormal signal.

The patient underwent a total thyroidectomy. The pathological results revealed that the left lobe nodule of thyroid was composed of follicular thyroid cancer tissue with peplos infiltration and tumor embolus formation of the small vessels.

Discussion

131I whole-body imaging is often used for the identification of metastatic lesions of differentiated thyroid cancer following total thyroidectomy (2,3). When thyroid tissues are not completely resected, 131I is largely absorbed by the existing normal thyroid tissues (5). However, metastatic lesions universally have a low uptake of 131I and, therefore, the metastatic lesions are not displayed clearly (5). As a result, 131I whole-body imaging is not generally selected to identify the metastatic lesions of thyroid cancer in the presence of normal thyroid tissues. 99mTcO4− is similar to the iodide ion to a certain extent (4); 99mTcO4− and the iodide ion are mediated by the sodium-iodide symporter and are absorbed by thyroid follicular cells (4). Therefore, the two methods are often used in thyroid imaging (6). However, 99mTcO4 imaging is not generally used to detect the metastatic lesions of thyroid cancer in the presence of thyroid tissues and also following a total thyroidectomy (6–8).

Follicular thyroid cancer tissues are mainly composed of differentiated follicular cells. The proteins of the sodium-iodide symporter are predominantly distributed in the membrane of follicular epithelial cells, and cancer tissues with follicular cells express sodium-iodide symporter proteins (9,10), which are the pacing factors for which 131I and 99mTcO4− are absorbed by the cancer tissues. The quantity of cancer tissues absorbing 99mTcO4− correlates with the level of sodium-iodide symporter protein expression. Since cancer tissues are not well-differentiated, the level of sodium-iodide symporter protein expression is low (10,11). Accordingly, the lesions of thyroid cancer frequently manifest ‘cool nodules’ or ‘cold nodules’ of decreased 99mTcO4− uptake (12). When thyroid tissues are not operated on, an increased 99mTcO4− uptake of metastatic lesions of thyroid cancer is rare. Certain studies have reported an increased uptake of neck metastases of thyroid cancer in 99mTcO4− thyroid imaging (7,8,13–15). However, to the best of our knowledge, there have been no studies with regard to the increased uptake of whole-body multiple metastatic lesions of thyroid cancer in 99mTcO4− whole-body imaging. The present study incidentally identified a mass outside of the thyroid gland in a patient with thyroid ‘cool nodules’, which exhibited increased 99mTcO4− uptake in the routine image field. Subsequently, a whole-body scan was performed. The result demonstrated that similar lesions of increased 99mTcO4− uptake existed in multiple positions of the whole body. CT, MRI and radionuclide whole-body bone imaging confirmed that the multitudinous sites of increased uptake, which were detected by 99mTcO4− imaging, contained tumor lesions. Therefore, despite the fact that 99mTcO4− imaging is not routinely used to identify metastatic lesions of thyroid cancer, when regional lesions of increased 99mTcO4− uptake are observed outside of the thyroid glands during routine field thyroid static imaging, further identification of the metastatic lesions of the whole body is significant.

Furthermore, 99mTcO4− whole-body imaging has numerous advantages. The procedure is highly sensitive, as shown by the third and fourth lumbar vertebral lesions and the ilium lesion, which were detected by 99mTcO4− imaging, but were not observed on the whole-body bone scan. MRI only identified the lesions of the fourth lumbar vertebra and the ilium, but not the third lumbar vertebral lesion. These results indicate that the sensitivity of 99mTcO4− whole-body imaging is higher than that of MRI and whole-body bone scan at this time. Furthermore, the procedure is highly specific. The fact that 99mTcO4− was able to be absorbed by thyroid cancer tissues under the mediation of sodium-iodide symporter proteins, confirms the diagnostic specificity for regional lesions. Abnormally increased 99mTcO4− uptake of the lesions outside of the thyroid glands is a characteristic of metastatic thyroid cancer tissues (7,8,13–15), suggesting that the lesions likely originated from thyroid tissues. Finally, the procedure increases the quality of the diagnosis of the thyroid nodules. For the patient of the present study, the feature of the ‘cool nodule’ was not enough to discriminate between malignant lesions and benign tumors. However, the identification of the metastatic lesions extremely supported the diagnosis of the malignant thyroid nodule. The 99mTcO4− imaging examination is able to scan the whole body of patients and, therefore, the detection area is extensive, which conduces to a complete detection of the lesions.

References