Otolaryngology #200402053

Dr. Russell Smith

Pre-op FDG-PET to detect malignant follicular neoplasm of the thyroid

Abstract:

A thyroid nodule is a common entity that can be detected on routine physical exam. The majority of thyroid nodules are benign, but approximately 5% of nodules are malignant. Fine needle aspiration (FNA) is currently utilized to evaluate a nodule for its potential of malignancy with the results accurately predicting whether the nodule is benign or malignant in many cases. Frequently, the cytologic diagnosis obtained after a FNA is a follicular neoplasm. To distinguish a follicular adenoma from a carcinoma, one must be able to identify either capsular or vascular invasion. Since these findings are not able to be assessed by a FNA, open biopsy is required to differentiate a follicular adenoma from a follicular carcinoma. A thyroid lobectomy is typically performed in this situation to exclude malignancy since no other diagnostic modality is currently available to establish the pathologic diagnosis. If the pathologic diagnosis is a follicular adenoma, no further therapy is necessary. But if the pathologic diagnosis is a follicular carcinoma, a second surgery for completion total thyroidectomy is required.

Positron emission tomography (PET) is frequently performed during the evaluation of several malignancies. PET imaging using fluorine-18-fluorodeoxyglucose (FDG) detects areas of increased glucose utilization and allows calculation of a standard uptake value (SUV). This SUV has been shown to correlate highly with the malignant potential of an area, with higher SUVs being more indicative of malignancy.

If FDG-PET imaging can differentiate benign from malignant follicular neoplasms pre-operatively, the management of patients with follicular neoplasms of the thyroid would be markedly altered. Patients with follicular carcinomas could be identified pre-operatively and receive definitive therapy with one surgery and avoid the consequences of multiple procedures. The potential also exists that in the future patients with follicular adenomas could avoid surgical intervention entirely.