Hyalinizing trabecular tumor: Sheep in the Wolf’s clothing! – A case report and review of the literature

ABSTRACT Hyalinizing trabecular tumor (HTT) is a rare neoplasm of follicular origin. It is often mistaken for classic papillary thyroid carcinoma (PTC) or medullary thyroid carcinoma (MTC) due to overlapping cytological and architectural features. We report a 49-year-old woman presenting with a left-sided thyroid nodule of 6 months’ duration. Ultrasound had shown a solid hypoechoic TIRADS 3 lesion (29 mm × 14 mm), and FNAC was suggestive of Bethesda category V. Her thyroid-stimulating hormone was 4.04 μIU/ml. She underwent total thyroidectomy with bilateral lymph node dissection. After histopathology, it showed a classic trabecular growth pattern and prominent hyalinization. Immunohistochemistry revealed a low proliferation index (Ki-67-peripheral staining), absent BRAF mutation, and PAS-positive, Congo red-negative stroma-differentiating it from PTC and MTC. A diagnosis of a hyalinizing trabecular tumor of the thyroid was made.