This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
A 30 year old female patient complains of painless hard anterior neck mass. FNAC was inconclusive. Open thyroid biopsy was performed which revealed the  ﬁbrous nature of the mass, woody, non tender thyroid, mimicking carcinoma is  observed.  The diagnosis points towards 
Select and explain. 
A. De Quervain's thyroiditis, B. Riedel's thyroiditis, C. Hashimoto’s thyroiditis, D. None of the above
B: Riedel's thyroiditis
Answer: B: Riedel's thyroiditis 
Explanation: None