Use of 18F-FDG-PET/CT (PET) staging for a variety of malignancies has increased in recent years. A rise in detection of incidental thyroid lesions creates a novel diagnostic challenge. We present four cases of Thyroid PET positivity.
A 62-year-old lady with pulmonary adenocarcinoma on contrast CT-Thorax had diffuse thyroid PET uptake. Biochemistry revealed a self-limiting TSH rise. Thyroid ultrasound showed benign nodular goitre (U2). Findings may have represented contrast-induced thyroiditis. Patient was referred for curative pulmonary upper lobectomy.
A 62-year-old gentleman with oesophageal adenocarcinoma had PET staging showing focal uptake within a right thyroid nodule. Thyroid biochemistry was normal. Ultrasound revealed a goitre with a U3 nodule right of the isthmus. Right thyroid lobectomy and isthmusectomy was undertaken. Histology confirmed a follicular variant of papillary carcinoma.
A 78-year-old lady undergoing work-up for pancreatic intraductal papillary mucinous neoplasm and lung cancer was found to have a PET-positive left thyroid nodule. Thyroid biochemistry and calcitonin were normal. Ultrasound with FNA showed a U3 nodule and Thy1 cytology respectively. Diagnostic left lobectomy was performed; histology showed a follicular adenoma.
A 42-year-old lady had a right lower lobe lesion on chest x-ray. Staging CT revealed a thyroid isthmus nodule with focal PET-positivity; lung lesion was benign. Thyroid Ultrasound revealed a U3 nodule; FNA suggested Thy3f cytology. Patient was referred for diagnostic thyroid lobectomy.
Incidental PET positive thyroid lesions present a diagnostic challenge when discovered alongside other malignancies requiring urgent staging investigations and treatment. The pattern of thyroid uptake appears indicative of the underlying aetiology. From published data, the risk of malignancy with focal uptake is between 23%35%. Diffuse thyroid uptake is usually benign. A standardised approach to promptly evaluate PET-positive thyroid incidentalomas is needed for timely management of these patients.