Diffuse sclerosing variant of thyroid papillary carcinoma: diagnostic challenges occur with Hashimoto's thyroiditis.

Diffuse sclerosing papillary thyroid carcinoma (DSPTC) is a relatively rare variant of papillary thyroid carcinoma with distinct histological features, radiological characteristics, and biological aggressiveness. Compared with conventional papillary thyroid carcinoma, DSPTC is characterized by scattered microscopic tumor islands, diffuse fibrosis, calcification, and abundant lymphocytic aggregation. A preoperative diagnosis is challenging in the absence of nodules and scanty fine needle aspiration cytology samples. We describe a unique DSPTC patient, an 18-year-old woman who presented with a neck mass that grew slowly for 2 years. The palpable neck mass was nontender, well defined, firm, and unmovable. Laboratory studies showed normal thyroid function and positive autoimmune markers: antithyroglobulin antibody = 1:1600 and antimicrosomal antibody = 1:1600. A neck ultrasound showed diffusely prominent microcalcifications with one small vague nodule. Hashimoto's thyroiditis with an accompanying malignancy was suspected. Based on the result of intraoperative pathology reports, the patient was given a total thyroidectomy. Lymph node dissection and histological analysis revealed bilateral DSPTC in addition to lymphocytic thyroiditis in nonmalignant areas of the thyroid. Clinical and histological diagnostic challenges usually occur when DSPTC presents with a diffuse thyroid enlargement, dispersed microscopic tumor islands (frequently without mass formation), extensive fibrosis, and abundant lymphocytic infiltration mimicking thyroiditis.