FDGPET Detected Thyroid Incidentaloma Dr LP Si Yan

FDG-PET Detected Thyroid Incidentaloma Dr. LP Si Yan Chai Hospital

Background �With the increasing use of imaging modalities, more and more clinically inconspicuous thyroid lesions are discovered �These are termed as thyroid incidentalomas �Also include asymptomatic thyroid lesions identified during non-thyroid neck surgery, eg. parathyroidecotmy, carotid endarterectomy

�Prevalence �USG: 67% �CT / MRI: 16% �Carotid duplex: 9. 4% �FDG-PET: 2 -3% �Increasing use of FDG-PET �Thyroid carcinomas detected by FDG-PET is more aggressive than those detected by other imaging modalities

FDG-PET �Fluorodeoxyglucose positron emission tomography �Mostly commonly used for �Disease staging for patients with known malignancy �Malignancy screening in healthy individuals

�Increase FDG uptake in metabolically active tissue, e. g. malignancy, infection, inflammation, etc �Normal thyroid gland not shown up

FDG-PET detected thyroid incidentalomas �Unsuspected, asymptomatic thyroid lesions discovered on FDG-PET �Prevalence 1. 2 -4. 8% �Increasing incidence but no increase in disease specific mortality �Risk of malignancy � 14 -74% �higher than incidental thyroid nodules found by USG, CT, or MRI

Is the thyroid incidentaloma on FDG-PET benign or malignant?

Pattern of uptake �Focal �Increase in radioactivity concentration compared to that of the thyroid parenchyma �Clearly delineated from the surrounding thyroid gland �Diffuse �Even distribution of FDG in the entire thyroid gland �Radioactivity concentration is higher than that of the surrounding soft tissue

Focal uptake

Diffuse uptake

�Focal uptake of thyroid lesions on PET also known as �PETomas �PET-associated incidental neoplasms (PAINs) �PET detected thyroid incidentalomas (PETI) �Associated with an increased risk of malignancy than diffuse uptake

20 out of 27 patients who underwent operation proved to have thyroid malignancy (74%) Nishimori H et al. Incidental thyroid “PETomas”: clinical significance and novel description of the self-resolving variant of focal FDG-PET thyroid uptake. Can J Surg Vol. 54, No. 2 , April 2011

SUV �Standardized uptake value �Elevated in metabolically active tissue �Controversies about the use of SUV as an adjunct to differentiate between benign or malignant �No cut off value

Katz SC et al. PET-Associated Incidental Neoplasms of the Thyroid. J Am Coll Surg (2008) 259 -264

�SUV correlates with the size of the thyroid incidentaloma in focal uptake �r = 0. 64, p < 0. 05 Nilsson IL et al. Thyroid Incidentaloma Detected by Flurordeoxyglucose Positron Emission Tomography/Computed Tomography: Practical Management Algorithm. World J Surg (2011) 35: 2691 -2697

Risk factors of malignancy �Clinically apparent thyroid nodules are associated with 5% malignant rate �Are et al. showed that risk of malignancy in the presence and absence of palpable thyroid nodule is 24% and 6. 3% respectively (p = 0. 01)

�Focal FDG uptake and unilateral uptake are associated with higher malignancy rate Are C et al. FDG-PET Detected Thyroid Incidentalomas: Need for Further Investigation? Annals of Surgical Oncology (2006) 14(1): 239 -247

FDG-PET detected incidental thyroid carcinomas �Most are papillary thyroid carcinoma (PTC) �Poor prognostic variants are more common �Tall-cell variant papillary thyroid carcinoma (TCVPTC) �Poorly differentiated thyroid carcinoma �As high as 50% �Extra-thyroidal extension is also more common �Higher treatment failure rate �Higher local, regional and distant recurrences �Higher disease-specific mortality

TCVPTC �More aggressive with a worse prognosis when compared to classical PTC (c. PTC) �High rate of extra-thyroidal extension �Up to 90% in one series �Commonly smaller than c. PTC �FNAC is warranted regardless of the size if the lesion is suspicious

Management �Most of the patients already have a primary malignancy → the whole plan of management should depend on the overall prognosis and life expectancy �USG thyroid is necessary for all patient �No evident nodule → follow up �Nodule ≥ 1 cm or < 1 cm with suspicious features → FNAC

�Suspicious sonographic features �Marked hypoechogenicity �Taller than wide �Irregular shape �Ill-defined margin �Punctate calcification �Increase in vascularity

�FNAC (Bethesda System) �Nondiagnostic �Benign �Atypia of undetermined significance (AUS) �Suspicious for follicular neoplasm / follicular neoplasm �Suspicious for malignancy �Malignant

FNAC results Action Non-diagnostic / AUS Repeat FNAC Benign Follow up Suspicious for follicular neoplasm / suspicious for malignancy / malignant Operation

Conclusion �FDG-PET detected thyroid incidentalomas harbour a significant risk of malignancy �Thyroid carcinomas detected on FDG-PET are more aggressive and demonstrate poorer prognosis �They should be investigated by USG +/- FNAC �Definitive management plan depends on the overall prognosis and life expectancy of the patients

References � American Thyroid Association Management Guidelines for Patients with Thyroid Nodules and Differentiated Thyroid Cancer (2009) � Jin J et al. Thyroid incidentaloma. Best Practice & Research Clinical Endocrinology & Metabolism 26 (2012) 83 -96 � Nilsson IL et al. Thyroid Incidentaloma Detected by Flurordeoxyglucose Positron Emission Tomography/Computed Tomography: Practical Management Algorithm. World J Surg (2011) 35: 26912697 � Ho TY et al. Prevalence and significance of thyroid uptake detected by 18 F-FDG PET. Endocrine (2011) 40: 297 -302 � Bertagna F et al. F 18 -PDF_PET/CT thyroid incidentalomas and their benign of malignant nature: a critical and debated issue. Ann Nucl Med (2011) 25: 151 -152 � Nishimori H et al. Incidental thyroid “PETomas”: clinical significance and novel description of the self-resolving variant of focal FDG-PET thyroid uptake. Can J Surg Vol. 54, No. 2 , April 2011 � Law TT et al. Incidental Thyroid Carcinoma by FDG-PET/CT: A Study of Clinicopathological Characteristics. Ann Surg Oncol (2011) 18: 472 -478

� Jin J et al. Incidental thyroid nodule: patterns of diagnosis and rate of malignancy. The American Journal of Surgery (2009) 197, 320 -324 � Kang BJ et al. Incidental thyroid uptake on F-18 FDG PET/CT: correlation with ultrasonography and pathology. Ann Nucl Med (2009) 23: 729 -737 � Gough J et al. Thyroid Incidentaloma: An Evidence-based Assessment of Management Strategy. World J Surg (2008) 32: 1264 -1268 � Katz SC et al. PET-Associated Incidental Neoplasms of the Thyroid. J Am Coll Surg (2008) 259 -264 � Are C et al. Histological Aggressiveness of Fluorodeoxyglucose Positron-Emission Tomogram (FDG-PET)-Detected Incidental Thyroid Carcinomas. Annals of Surgical Oncology (2007) 14(11): 3210 -3215 � Are C et al. FDG-PET Detected Thyroid Incidentalomas: Need for Further Investigation? Annals of Surgical Oncology (2006) 14(1): 239 -247