Which of the following histological features is pathognomonic for Hashimoto's thyroiditis?

Explanation

## Histological Features of Hashimoto's Thyroiditis **Key Point:** Hashimoto's thyroiditis is characterized by a chronic lymphocytic infiltration with germinal centers (indicating active B-cell response) and the presence of Hürthle cells (oncocytic change in thyroid follicular epithelium). ### Microscopic Hallmarks | Feature | Hashimoto's | Graves' | Subacute | Acute | |---------|-------------|---------|----------|-------| | **Infiltrate type** | Lymphocytes + plasma cells | Lymphocytes (minimal) | Granulomas | Neutrophils | | **Germinal centers** | Present (++++) | Absent | Absent | Absent | | **Hürthle cells** | Prominent | Absent | Absent | Absent | | **Fibrosis** | Late stage | Minimal | Minimal | Minimal | | **Follicular destruction** | Progressive | Minimal | Moderate | Severe | **High-Yield:** Hürthle cells (also called Askanazy cells or oncocytes) are metaplastic thyroid follicular cells with abundant mitochondria, giving them a granular, eosinophilic cytoplasm. Their presence in a lymphocytic infiltrate is virtually diagnostic of Hashimoto's thyroiditis. **Clinical Pearl:** The germinal centers within the lymphoid infiltrate represent active autoimmune response with B-cell proliferation and antibody production against thyroid peroxidase (TPO) and thyroglobulin. ### Why This Matters - Distinguishes Hashimoto's from other forms of thyroiditis on histology alone - Reflects the autoimmune nature of the disease - Hürthle cell change is a response to chronic lymphocytic injury