Macrofollicular subtype of papillary thyroid carcinoma: Ultrasonographic findings and clinical implications

The macrofollicular subtype of papillary thyroid cancer (MFS-PTC) is a rare subtype often leading to a challenging diagnosis. To evaluate the ultrasonographic (US) features and clinical implication of MFS-PTC. Records of 14 patients histologically diagnosed with MFS-PTC at our institution over a period of 16 years were retrospectively reviewed. Preoperative US features, Bethesda categories determined by fine-needle aspiration (FNA) or core needle biopsy (CNB), and final pathology were assessed in all patients with MFS-PTC. Of the 14 MFS-PTC cases, most nodules were noted as smooth marginated, solid or predominantly solid isoechoic on US and were categorized as low suspicion in 12 cases and intermediate suspicion in 2 cases. The median tumor size was 1.2 cm (range, 0.6-5.6 cm). Of 11 cases that underwent FNA or CNB, 4 (36.4%) with Bethesda category II or III underwent the follow-up because of benign-looking appearance on US and benign results in subsequent CNBs. However, the patients underwent delayed surgery (31.3 months, range 12-41 months) because of serially increased tumor size. Seven patients diagnosed with Bethesda type IV, V, and VI subsequently underwent surgery. Gross extrathyroidal extension into subcutaneous fat tissue and lateral lymph node metastasis were noted in a patient who underwent follow-up. No distant metastases or recurrence was detected. MFS-PTC is representative of a benign sonographic appearance of PTC subtypes. Tumor growth on serial US images is the only suspicious finding for MFS-PTC because FNA or CNB is often false negative.