A 55-year-old woman presents with a hard, fixed, painless thyroid mass causing dysphonia and dysphagia. ESR is normal. Biopsy shows dense keloid-like fibrosis, obliterative phlebitis, and inflammation extending into surrounding neck structures. IgG4-positive plasma cells are increased. The diagnosis is:
- A Anaplastic thyroid carcinoma with sclerosis
- B Invasive fibrous variant of Hashimoto thyroiditis
- C Reidel thyroiditis ✓
- D Subacute granulomatous thyroiditis
Correct answer: C. Reidel thyroiditis
Explanation
Riedel thyroiditis is characterized by a hard, woody thyroid with dense fibrosis extending beyond the capsule into surrounding structures, obliterative phlebitis, and can be associated with IgG4-related disease. It is distinct from Hashimoto thyroiditis (lymphoid follicles, Hurthle cells), anaplastic carcinoma (malignant cells), and subacute thyroiditis (granulomatous inflammation, painful, elevated ESR).
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.