This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thyroid, Subject name: Surgery
Riedel's thyroiditis is associated with: 
Select and explain. 
A. Hypehyroidism, B. Retroperitoneal fibrosis, C. Hyperparathyroidism, D. Non-palpable thyroid gland
B: Retroperitoneal fibrosis
Answer: B: Retroperitoneal fibrosis 
Explanation: Riedel's Thyroiditis Aka Invasive Fibrous thyroiditis Characterized by complete replacement of thyroid and parathyroid glands by fibrous tissue. Associated with Retro orbital fibrosis Periorbital fibrosis Retroperitoneal fibrosis Sclerosing cholangitis Management Lifelong levothyroxine (due to permanent hypothyroidism) Lifelong calcium and Vitamin D supplementation (due to permanent hypoparathyroidism