(A535) Diagnostic Pitfalls in Thyroid Ultrasound: Recognizing Diffuse Sclerosing Papillary Thyroid Carcinoma

Introduction: Diffuse sclerosing papillary thyroid carcinoma (DSPTC) is a rare, aggressive subtype of papillary thyroid carcinoma (PTC) marked by diffuse thyroid infiltration rather than formation of discrete nodules, with a propensity for extrathyroidal extension and nodal metastasis. Recognizing its unique and variable ultrasound (US) features and identifying suspicious lymph nodes may prevent diagnostic delays.

Methods: Case study of a 37-year-old female diagnosed with DSPTC by fine needle aspiration (FNA) of a lymph node.

Results: A 37-year-old female presented after palpating a lymph node in her right neck. Initial US revealed mild to moderate cervical lymphadenopathy and benign-appearing generalized thyroid heterogeneity. Suspected lymphocytic thyroiditis prompted endocrinology referral where point-of-care US identified many pathologic-appearing cervical lymph nodes in the central and bilateral lateral neck and a heterogenous, hyperechoic thyroid with diffuse punctate echogenic foci without obvious nodularity. Lymph node FNA revealed PTC. The patient underwent total thyroidectomy and bilateral compartment dissections. Pathology confirmed DSPTC involving the entire thyroid and 19 of 71 lymph nodes positive for malignancy.

Conclusions: DSPTC is rare, accounting for < 6% of PTC cases. Its diffuse infiltration of the thyroid can mimic benign conditions like Hashimoto’s thyroiditis, leading to US misinterpretation and delayed recognition of malignancy. Classic US characteristics include heterogenous (often hypoechoic) echotexture and diffuse microcalcifications with a “snowstorm appearance,” with involvement ranging from poorly defined nodules to the entire gland. Early identification of suspicious cervical lymph nodes is crucial, as over 80% of DSPTC cases present with regional metastases. In hindsight, DSPTC was missed on initial US due to diffuse gland involvement and lack of a discrete nodule. Repeat US lead to identification and biopsy of suspicious lymph nodes, resulting in definitive diagnosis and highlighting the critical role of cervical lymph node evaluation in thyroid assessments.