Clinical presentation: A 59-year-old woman was referred for aspiration cytology of a "cold" nodule. She was first diagnosed having Hashimoto's thyroiditis 23 years ago. Recently she had complaints suggesting hyperthyroidism. On evaluation subclinical hyperthyroidism was disclosed. Scintigraphy revealed a "hot" nodule in the right and a "cold" nodule in the left lobe.

Palpation: The thyroid was not palpable.

Laboratory tests: TSH 0.04 mIU/L, FT4 15.4 pM/L, FT3 3.37 pM/L, aTPO was > 3000 U/mL, TSAb 0 U/L.

Ultrasound. The thyroid contained multiple discrete areas of various echogenicities. There was no nodule in the right lobe. There was a nodule in the left lobe according to the cold area on scintiscan. While there were no nodules in pathological sense in the right lobe, the lesion in the left lobe is very likely a nodule in pathological sense.

Aspiration cytology from the right nodule resulted in benign lesion.

Suggestion. We offered a wait-and-see. Three months later hypothyroidism has developed which resolved spontaneously another 6 months later.

Comments.

1. The isotope uptake is heterogeneous in Hashimoto's thyroiditis. The overinterpretation of increased uptake as an autonomously functioning nodule is a relatively frequent failure.

2. The judgement of the echogenicity of the nodule in the left lobe depends on how to define the reference normal thyroid. If it is the extralesional part than the nodule is iso/hyperechoic and according to most TIRADS does not require FNA. Is the reference tissue is the healthy thyroid, than the nodule should be involved among hypoechoic nodules and is a candidate for FNA.