Sonographic appearances of hobnail papillary thyroid carcinoma: A case report of a rare tumour.

Introduction: Hobnail papillary thyroid carcinoma is a rare, recently described papillary thyroid carcinoma variant, with potential for a more aggressive clinical course of disease and poorer prognosis. Case report: A 53-year-old man presented with a left thyroid mass. The ultrasound features of this mass included a predominantly cystic appearance with mobile internal echoes, vascularised internal septations, and murally based solid material. These ultrasound features were not deemed malignant by classification standards, which led to the patient being managed with active surveillance. However, the mass grew quickly and the patient underwent diagnostic hemithyroidectomy which led to hobnail variant papillary thyroid carcinoma being found on pathology. Discussion: The ultrasound features of the hobnail variant of papillary thyroid carcinoma have not been previously described in detail in the literature and, in this case, are features that would not be deemed malignant by classification standards. The rapid growth of the mass is what led to clinical suspicion of malignancy and resulted in diagnosis. Conclusion: The hobnail variant of papillary thyroid carcinoma may not have typical ultrasound findings associated with malignancy. Careful clinical correlation is advised in order to discern this difficult diagnosis and to facilitate appropriate treatment.