Thyroid carcinoma metastatic to the skeleton with intense associated hypermetabolic activity

A 70-year-old man with history of hypertension, diabetes and chronic kidney disease was diagnosed with an early stage right papillary thyroid carcinoma in 1999.

This was initially treated by total thyroidectomy and radioactive iodine ablation with pathology indicating extrathyroidal extension into skeletal muscle and one parathyroid gland. He had a local recurrence in 2003 when he was found to have a subcutaneous nodule at the side of incision. This was excised locally along with a right modified radical neck dissection followed by another dose of radioactive iodine.

Post-operative study demonstrates distortion along the glottic region by presumed post-operative changes. The red circle denotes a submental lymph node, which was indeterminant. Images courtesy of M. Gehsani, MD

Follow-up PET/CT examination again demonstrates distortion of the glottic region and increased soft tissue with corresponding mild hypermetabolic activity with a maximal standard uptake value of 2.4. Note resolution of the previously seen submental lymph node.

He had been continuing on thyroid-stimulating hormone suppressive therapy with thyroxine and had regular follow-up exams. However, he had multiple local recurrences requiring surgical resection, including partial laryngeal resection and tracheotomy. He underwent a FDG-PET/CT scan in 2010 that was concerning for distant metastases. There was increased fullness in the soft tissues within the thyroid bed without any discrete mass on the CT portion. There was fullness of the pretracheal soft tissues inferior to the tracheostomy stoma demonstrating a low grade metabolic activity with a maximum standard uptake value of 2.4. However, there was a new hypermetabolic lytic lesion along the left iliac bone with standard uptake value of 8.3, consistent with skeletal metastases.

This image demonstrates clips along the thyroidectomy bed. There was no evidence of recurrence at the time.

Follow-up PET/CT demonstrates placement of a tracheostomy tube. The thyroidectomy bed demonstrates mild hypermetabolic activity with a maximal standard uptake value of 3.4.

The remarkable difference between low grade diffuse metabolic activity in the local treatment bed as opposed to the well-defined round focus of intense hypermetabolic activity in the distant metastases makes it more likely that the former is due to post-therapy changes rather than local/regional recurrence. Currently, the patient is being evaluated for further management of his distant metastatic disease.

This image is representative of the osseous structures failing to demonstrate osseous metastases.

On the follow-up PET/CT, a new lytic lesion is seen along the left iliac bone with corresponding intense hypermetabolic activity with a maximal standard uptake value of 8.3. Due to this distant metastasis showing intense FDG uptake, it is presumed that the mild hypermetabolic activity along the thyroidectomy bed and glottic region is post-operative and not indicative of local recurrence.

Case Discussion

The incidence of thyroid cancer has been increasing in the past decade. This is partly due to the earlier detection of subclinical disease by ultrasonography and biopsy of the thyroid nodules. The treatment of differentiated papillary and follicular thyroid cancers includes combination of surgery, radioiodine ablation and thyroid hormone suppression. The prognosis is generally excellent with 5-year survival about 90% in patients without metastatic disease. Prognostic factors related to cancer recurrence and mortality include age, size of the primary tumor, soft tissue invasion and distant metastases.

Robbins and colleagues showed the importance of FDG-PET as a prognostic tool in patients with metastatic disease. Patients who had a positive FDG scan were more likely to have increased cancer-related mortality compared with patients with negative FDG scans. Also, the patients with only locally positive FDG activity had a better survival than those with distant sites of FDG activity. Thus, the role of FDG-PET scanning in thyroid cancer has been increasing from localization imaging to providing important prognostic information.

The PET scans are especially useful in patients with negative radioiodine uptake and both of these imaging modalities complement each other to evaluate distant metastatic disease. The well-differentiated cancers can become less differentiated and fail to take up iodine, making the radioiodine scans less sensitive. However, these less differentiated cancers may have an increased metabolic activity and a high FDG uptake, resulting in improved sensitivity of FDG-PET scanning.

Recent meta-analysis by Dong and colleagues showed that the pooled sensitivity and specificity of FDG-PET scan in patients with elevated thyroglobulin levels and a negative radioiodine scan was 88.5% and 84.7%, respectively. The long-term follow-up of these patients usually includes clinical examinations, serum thyroglobulin levels and neck imaging using ultrasonography. In patients with a clinical suspicion of recurrence, additional imaging including radioiodine scan and FDG-PET/CT scans can be used to identify the sites of metastases.

Sumit Talwar, MD, is hematology oncology fellow at St Luke’s-Roosevelt Hospital Center.

Neil Gupta, MD, is a resident in radiology at St Luke’s-Roosevelt Hospital Center.

Daniel B. Kuriloff, MD, FACS, is director of the Center for Thyroid and Parathyroid Surgery, The New York Head and Neck Institute, and associate clinical professor, Otolaryngology-Head and Neck Surgery, at Columbia University College of Physicians and Surgeons.

Munir Ghesani, MD, is an attending radiologist at St. Luke’s-Roosevelt Hospital Center and associate clinical professor of radiology at Columbia University College of Physicians and Surgeons.

For more information:

• Dong MJ. Nucl Med Commun. 2009;30:639-650.
• Robbins RJ. J Clin Endocrinol Metab. 2006;91(2): 498-505.