“White-Knight” Nodule

A 69-year-old female with a history of long-standing hypothyroidism was referred to our clinic for a thyroid nodule. She was started on levothyroxine replacement a decade earlier due to symptoms of biochemically-confirmed hypothyroidism. 

History. Two years earlier, she was noted to have an incidental, solitary, well-circumscribed, hyperechoic thyroid nodule in the inferior mid-right thyroid lobe, measuring 2.6 cm x 1.9 cm x 1.9 cm (Figure 1). Fine needle aspiration biopsy of this nodule showed follicular cells, Hurthle cells, numerous small and large lymphocytes, and colloid—consistent with chronic lymphocytic thyroiditis (Figure 2). She denied any compressive symptoms and the thyroid nodule was not palpable on examination. 

Laboratory tests. Biochemical work-up showed a TSH of 0.042 uIU/mL (normal 0.4-5.1 uIU/mL) and a free T4 of 1.5 ng/dL (normal 0.7-1.6 ng/dL) consistent with exogenous subclinical hyperthyroidism. Her antithyroid peroxidase antibody was markedly elevated at >1300 U/mL (normal ≤59 U/mL). Follow-up thyroid ultrasonography showed the previous hyperechoic thyroid nodule measuring 2.5 cm x 2.0 cm x 1.6 cm (Figure 3). 

Discussion. The “White-Knight” nodule—a well-defined, isovascular or without vascularity, with absent calcifications¹—is a subset of hyperechoic thyroid nodules associated with Hashimoto’s thyroiditis (HT), the most common cause of hypothyroidism in the United States. HT commonly presents as a diffusely enlarged thyroid with a coarsened hypoechoic texture on ultrasonography.² About 4% to 5% of patients with HT may present as nodular HT.² These hyperechoic nodules are thought to be regenerative nodules of HT,¹ and are benign.^1,3 

The widespread utility of ultrasonography has led not only to increased thyroid cancer diagnosis, but also to numerous thyroid incidentalomas and unnecessary fine needle aspirations, which may impact healthcare costs. Biopsy could be avoided in these nodules as malignancy risk is low. Re-evaluation of present guidelines on thyroid biopsy for nodules having these characteristics may be necessary.

References: 

1. Bonavita JA, Mayo J, Babb J, et al. Pattern recognition of benign nodules at ultrasound of the thyroid: which nodules can be left alone? AJR Am J Roentgenol. 2009;193(1):207-213. 

2. Anderson L, Middleton WD, Teefey SA, et al. Hashimoto thyroiditis: Part 1, sonographic analysis of the nodular form of Hashimoto thyroiditis. AJR Am J Roentgenol. 2010;195(1):208-215. 

3. Virmani V, Hammond I. Sonographic patterns of benign thyroid nodules: verification at our institution. AJR Am J Roentgenol. 2011;196(4):891-895.