¹⁸F-FDG PET of Patients with Hürthle Cell Carcinoma

MATERIALS AND METHODS

RESULTS

Fourteen ¹⁸F-FDG PET scans of 12 patients were obtained in the time frame indicated. Ten of the PET scans were for evaluation of morphologic abnormalities found by other imaging techniques. Of the other 4 patients, 2 were imaged without any other suspected abnormalities, 1 for a positive finding on physical examinations, and 1 for an elevated thyroglobulin level. The patient group included 7 men and 5 women with an average age of 47 y (range, 38–78 y). All patients had previous biopsy-proven Hürthle cell carcinoma. Eleven of the 12 patients were being evaluated for recurrent Hürthle cell carcinoma, and 1 patient was undergoing disease staging for the planning of initial therapy. In patients with previous disease, the mean time from diagnosis to the time of evaluation was 4.4 y (range, 5 mo to 15 y). At the time of evaluation, Hürthle cell carcinoma was shown to be present in 13 patients, as confirmed by pathology in 10 and by clinical follow-up in 3. One patient (patient 7), who had undergone subtotal thyroidectomy 1 mo before, was shown to be disease free on all imaging tests except iodine imaging, which was equivocal; was biopsy negative in the neck by fine-needle aspiration; and was disease free 1 y later on follow-up. PET findings were positive, with intense ¹⁸F-FDG uptake, in all but 1 of these 13 patients with known disease (92% sensitivity).

Disease not identified by other imaging methods was shown in 7 of the 14 PET scans obtained (Table 1). PET identified distant metastatic disease (6) or local disease (2) that was more extensive than otherwise demonstrated (1 patient had both more extensive local disease and distant disease shown by PET). Of these 8 areas of disease, 5 were proven by biopsy, 2 were confirmed by other imaging methods, and 1 was considered positive on the basis of other clinical data (Figs. 1 and 2). For 7 of 14 scans, the information provided by PET was used to guide or change therapy. Of 7 patients who had iodine scans, 6 had negative findings and 1 scan was read as questionable. In the 1 PET scan that was read as negative, there was substantial nonspecific neck uptake, probably because of muscle or fat uptake, that may have obscured the 1 focal site of disease then thought to exist (Fig. 3). The focus as seen on sonography was 1.8 × 1.1 × 0.9 cm. Three months later, this site was resected and proven to be grade 2/4 Hürthle cell recurrence. On retrospective review of the PET data, the area in question did show moderate metabolism, but the finding was not obvious.

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FIGURE 1.

PET image of patient 2, who had history of Hürthle cell cancer and returned with complaint of diffuse aches. Single indeterminate lung nodule with some mediastinal adenopathy was seen on CT. Sonography and ¹³¹I scans had negative findings. PET image showed widespread bone and lung metastases, which were confirmed with right hilar biopsy.

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FIGURE 2.

PET image of patient 8, who had Hürthle cell cancer previously treated and who returned with elevated thyroglobulin level (800 ng/mL) for evaluation. Neck sonography and ¹³¹I scan had negative findings. PET image showed lung, vertebral body, and pelvis/femur (arrow) metastases. Biopsy of pelvis confirmed metastatic disease.

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FIGURE 3.

PET image of patient 9, who had Hürthle cell cancer previously treated and who returned for follow-up evaluation. Neck sonography showed 1-cm right-neck lymph node suggestive of Hürthle cell cancer. PET image showed variable nonspecific uptake in neck and chest, and no definite tumor was believed to be present. Biopsy 2 mo later of region seen on sonography confirmed disease (2/4 grade Hürthle cell cancer), which was also likely near right-lower-neck uptake seen on PET (arrow).

DISCUSSION

Hürthle cell carcinoma is an aggressive thyroid cancer that may require more aggressive locoregional therapy than other thyroid malignancies. This tumor is more commonly metastatic, and a thorough evaluation for distant metastasis is recommended. Hürthle cell carcinoma is also quite rare, with little published on imaging of this malignancy with PET.

In this review, we have shown that ¹⁸F-FDG PET is likely to show regions of active involvement by Hürthle cell cancer. Most areas of tumor demonstrated intense ¹⁸F-FDG uptake that was similar in intensity to that seen in other highly metabolically active malignancies. In the 1 case that was falsely negative on PET, other confounding uptake of ¹⁸F-FDG in the neck may have hampered the detection of a small focus (1 cm) of disease. The disease in this case was also of low grade (2/4), possibly reducing ¹⁸F-FDG uptake. Retrospective review of this case showed that moderate uptake was present in the region of the disease but was difficult to detect. New advances such as PET/CT fusion may improve the accuracy of PET in such cases.

PET provided additional information on disease extent that led to a change in patient care for 50% (7/14) of the scans obtained. The change in care was due to better characterization of indeterminate abnormalities on CT or sonography for 3 scans and to detection of unsuspected disease for 4 scans. The contribution of PET in the patient group was dramatic and certainly comparable with other data reporting clinical management changes resulting from PET in other ¹⁸F-FDG–avid malignancies such as colorectal and lung cancer (12). Our data support the results of Plotkin et al. (11), who described accurate identification of Hürthle cell carcinoma by ¹⁸F-FDG PET in a group of 17 patients with indications of recurrent disease.

Our data are limited in that the number of patients in our study was low. However, considering that this malignancy is uncommon, larger groups of patients will be difficult to obtain. Another limitation is that this study was a retrospective review, with all the inherent biases of such. Referral of these study patients for PET may well have been prompted by existing clinical dilemmas. The high rate with which PET affected management could thereby be somewhat exaggerated and might not be seen in a group of patients who are referred prospectively.

CONCLUSION

Hürthle cell carcinoma demonstrates intense uptake on ¹⁸F-FDG PET. Relative to anatomic or iodine imaging, PET improved staging and disease management in patients with Hürthle cell carcinoma. ¹⁸F-FDG PET should be recommended for the evaluation and clinical management of patients with Hürthle cell carcinoma.