Differential Diagnosis for a Single Thyroid Nodule
Single Most Likely Diagnosis
- Benign Thyroid Adenoma: This is the most common cause of a single thyroid nodule, often discovered incidentally during physical examination or imaging studies for other reasons. Most thyroid adenomas are non-functional (do not produce thyroid hormones) and are typically benign.
Other Likely Diagnoses
- Colloid Cyst: A type of benign thyroid nodule that arises from the thyroid gland's follicles. It can sometimes be filled with fluid, making it appear cystic on ultrasound.
- Thyroid Hemorrhage into a Pre-existing Nodule: Bleeding into a pre-existing thyroid nodule can cause it to suddenly enlarge and become painful.
- Follicular Neoplasm: This includes both benign follicular adenomas and malignant follicular carcinomas. The distinction between these two often requires histopathological examination after surgical removal.
- Papillary Thyroid Carcinoma: Although less common than benign causes, papillary thyroid carcinoma is the most common type of thyroid cancer and can present as a single nodule.
Do Not Miss Diagnoses
- Medullary Thyroid Carcinoma: A rare type of thyroid cancer that can produce calcitonin, which can be measured to aid in diagnosis. It has a genetic component and can be part of multiple endocrine neoplasia syndromes.
- Anaplastic Thyroid Carcinoma: A very aggressive and rare form of thyroid cancer. Early diagnosis is crucial, although it often presents at an advanced stage.
- Metastasis to the Thyroid: Rarely, cancers from other parts of the body can metastasize to the thyroid gland, presenting as a single nodule.
Rare Diagnoses
- Thyroid Lymphoma: A rare malignancy of the thyroid gland, often associated with chronic lymphocytic thyroiditis (Hashimoto's thyroiditis).
- Teratoma or Dermoid Cyst: Very rare, these can occur in the thyroid region and may contain elements from all three germ layers.
- Parathyroid Adenoma: Although not a thyroid nodule per se, a parathyroid adenoma can sometimes be mistaken for a thyroid nodule due to its location near the thyroid gland.
- Ectopic Thyroid Tissue: Abnormal location of thyroid tissue, which can sometimes be mistaken for a nodule in the thyroid gland itself.