Thyroid parenchymal expansion can result from diffuse enlargement or infiltration of the thyroid gland or from the presence of one or more thyroid nodules.
A thyroid nodule is a discrete lesion distinct from the surrounding thyroid parenchyma. Enlargement of other nearby anatomical structures, such as the parathyroid glands or regional lymph nodes, as well as branchial cleft and thyroglossal duct cysts, may sometimes be confused with thyroid nodules. Thyroid nodules may be palpable at presentation or may be incidentally detected during an imaging procedure (40% are self-identified, 30% are physician-identified, and 30% are incidentally discovered on imaging).
Incidental detection, in addition to the use of thyroid ultrasonography for surveillance, is thought to be behind an increased reported incidence of thyroid cancers throughout the industrialised world. Neck ultrasonography performed for other indications detects thyroid nodules in more than 20% of the population. Incidental nodules are more common in female patients. Autopsy studies detect nodules in over half of the general population by the fifth or sixth decades of life.
Most nodules are benign and only 5% to 12% of the nodules detected on ultrasonography are malignant. Most thyroid nodules, including thyroid cancers, are asymptomatic. The clinical conundrum in the evaluation of the thyroid nodule is differentiating a benign from a malignant lesion.
Management of thyroid nodules is based on sonographic characteristics and cytology from fine needle aspiration biopsy (FNA). Molecular biomarkers are being increasingly used to enhance the diagnostic clarity from the FNA in patients with follicular neoplasms (Bethesda IV, using the Bethesda system for reporting thyroid cytopathology) and follicular lesions of unknown significance (Bethesda III). Routine biopsy of lesions <1 cm in greatest diameter should be discouraged.
The concept of risk stratification of patients presenting with thyroid nodules that end in a malignant cytological diagnosis is key to understanding the management approach for thyroid cancer. It serves as an objective way of prescribing the extent of surgical resection to patients with thyroid cancer, and has been illustrated based upon an escalating scale of known risks.
Based upon experience in Japan, there is a movement to offer observation of thyroid nodules (biopsy-proven papillary cancers or ultrasonographically suspicious nodules prior to biopsy) to selected patients pending tumour/neck ultrasound characteristics (e.g., primary tumour size and location within the thyroid), individual circumstance (e.g., willingness to accept surveillance, age, comorbid conditions), and the experience of the multidisciplinary clinical team. One way to avoid observing known microcarcinomas is to use restraint in biopsying lesions <1 cm in diameter.
- Colloid nodule
- Thyroid adenoma or hyperplastic nodule, single (solid or complex)
- Non-toxic multinodular goitre
- Differentiated thyroid cancer (papillary, follicular)
- Toxic adenoma, single
- Toxic multinodular goitre
- Medullary thyroid cancer
- Anaplastic thyroid cancer
- Simple epithelial-lined thyroid cyst
- Thyroglossal duct cyst
- Acute suppurative thyroiditis
- Subacute granulomatous thyroiditis
- Chronic lymphocytic (Hashimoto's) thyroiditis
- Painless lymphocytic thyroiditis
- Graves' disease
- Enlarged parathyroid gland(s): benign
- Parathyroid carcinoma
- Metastasis from non-thyroidal malignancies
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