Dr. LP SiYan Chai Hospital

BackgroundWith the increasing use of imaging

modalities, more and more clinically inconspicuous thyroid lesions are discovered

These are termed as thyroid incidentalomasAlso include asymptomatic thyroid lesions

identified during non-thyroid neck surgery, eg. parathyroidecotmy, carotid endarterectomy

PrevalenceUSG: 67%CT / MRI: 16%Carotid duplex: 9.4%FDG-PET: 2-3%

Increasing use of FDG-PETThyroid carcinomas detected by FDG-PET is

more aggressive than those detected by other imaging modalities

FDG-PETFluorodeoxyglucose positron emission

tomographyMostly 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 mortalityRisk of malignancy

14-74%higher than incidental thyroid nodules

found by USG, CT, or MRI

Pattern of uptakeFocal

Increase in radioactivity concentration compared to that of the thyroid parenchyma

Clearly delineated from the surrounding thyroid gland

DiffuseEven distribution of FDG in the entire thyroid

glandRadioactivity concentration is higher than that

of the surrounding soft tissue

Focal uptake

Diffuse uptake

Focal uptake of thyroid lesions on PET also known asPETomasPET-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

SUVStandardized uptake valueElevated in metabolically active tissueControversies about the use of SUV as an adjunct

to differentiate between benign or malignantNo 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 malignancyClinically apparent thyroid nodules are

associated with 5% malignant rateAre 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 carcinomasMost are papillary thyroid carcinoma (PTC)Poor prognostic variants are more common

Tall-cell variant papillary thyroid carcinoma (TCVPTC)

Poorly differentiated thyroid carcinomaAs high as 50%

Extra-thyroidal extension is also more commonHigher treatment failure rateHigher local, regional and distant recurrencesHigher disease-specific mortality

TCVPTCMore aggressive with a worse prognosis

when compared to classical PTC (cPTC)High rate of extra-thyroidal extension

Up to 90% in one seriesCommonly smaller than cPTCFNAC is warranted regardless of the size if

the lesion is suspicious

ManagementMost 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 patientNo evident nodule → follow upNodule ≥ 1cm or < 1cm with suspicious

features → FNAC

Suspicious sonographic featuresMarked hypoechogenicityTaller than wideIrregular shapeIll-defined marginPunctate calcificationIncrease in vascularity

FNAC (Bethesda System)NondiagnosticBenignAtypia of undetermined significance (AUS) Suspicious for follicular neoplasm / follicular

neoplasmSuspicious for malignancyMalignant

FNAC results Action

Non-diagnostic / AUS Repeat FNAC

Benign Follow up

Suspicious for follicular neoplasm / follicular neoplasm / suspicious for malignancy / malignant

Operation

ConclusionFDG-PET detected thyroid incidentalomas

harbour a significant risk of malignancyThyroid 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) 35:2691-2697

Ho TY et al. Prevalence and significance of thyroid uptake detected by 18F-FDG PET. Endocrine (2011) 40:297-302

Bertagna F et al. F18-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