Summary
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 anatomic 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).[1]
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 industrialized 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.[2][3] Autopsy studies detect nodules in over half of the general population by the fifth or sixth decades of life.[4]
Most nodules are benign and only 5% to 12% of the nodules detected on ultrasonography are malignant.[5][6] 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.[7]
[Figure caption and citation for the preceding image starts]: The Bethesda system for reporting thyroid cytopathology: recommended diagnostic categories, implied risk of malignancy, and recommended clinical management. Risk percentages depend on rates of atypia and follicular lesion as reported by local pathologists. It is important for surgeons to have a good understanding of the pathologist's rationale and reporting rates of the various Bethesda classified thyroid nodules. Management may depend upon many factors such as size, associated symptoms, and patient anxiety, as well as fine needle aspiration (FNA) interpretationCreated by the BMJ Knowledge Centre; adapted from Bumpous J, Celestre MD, Pribitkin E, et al. Decision making for diagnosis and management: algorithms from experts for molecular testing. Otolaryngol Clin North Am. 2014 Aug;47(4):609-23 [Citation ends].
The concept of risk stratification of patients presenting with thyroid nodules that end in a malignant cytologic diagnosis is key to understanding the management approach for thyroid cancer.[7] 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.
[Figure caption and citation for the preceding image starts]: Risk of structural disease recurrence in patients without structurally identifiable disease after initial therapy (DTC, differentiated thyroid cancer; ETE, extrathryroidal extension; FTC, follicular thyroid cancer; FV, follicular variant; LN, lymph node; PTMC, papillary thyroid microcarcinoma; PTC, papillary thyroid cancer. *BRAF/TERT status not routinely recommended for initial risk stratification. † Risk percentage estimates are best estimates based upon published literature)Created by the BMJ Knowledge Centre; adapted from Haugen BR, Alexander EK, Bible KC, et al. 2015 American Thyroid Association management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer. Thyroid. 2016 Jan;26(1):1-133 [Citation ends].
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 tumor/neck ultrasound characteristics (e.g., primary tumor 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.[8][9][10] One way to avoid observing known microcarcinomas is to use restraint in biopsying lesions <1 cm in diameter.
Differentials
Common
- Colloid nodule
- Thyroid adenoma or hyperplastic nodule, single (solid or complex)
- Nontoxic multinodular goiter
- Differentiated thyroid cancer (papillary, follicular)
Uncommon
- Toxic adenoma, single
- Toxic multinodular goiter
- Medullary thyroid cancer
- Anaplastic thyroid cancer
- Lymphoma
- Simple epithelial-lined thyroid cyst
- Thyroglossal duct cyst
- Acute suppurative thyroiditis
- Subacute granulomatous thyroiditis
- Chronic lymphocytic (Hashimoto) thyroiditis
- Painless lymphocytic thyroiditis
- Graves disease
- Enlarged parathyroid gland(s): benign
- Parathyroid carcinoma
- Metastasis from nonthyroidal malignancies
Contributors
Authors
Brendan C. Stack Jr, MD, FACS, FACE
Chair, Publications Committee
American Thyroid Association
Executive Board, Endocrine Section
American Head and Neck Society
Professor
Department of Otolaryngology-Head and Neck Surgery
University of Arkansas for Medical Sciences (UAMS)
UAMS Thyroid Center
Little Rock
AR
Disclosures
BCS is an author of a number of references cited in this topic.
Acknowledgements
Dr Brendan C. Stack would like to gratefully acknowledge Dr Steven P. Hodak and Dr Hussain Mahmud, the previous contributors to this topic. SPH and HM declare that they have no competing interests.
Peer reviewers
Renee E. Amori, MD
Assistant Professor of Medicine
Division of Endocrinology
Drexel University College of Medicine
Philadelphia
PA
Disclosures
REA declares that she has no competing interests.
Paul V. Carroll, MD, MRCPI, FRCP
Consultant Endocrinologist
Guy’s & St. Thomas’ NHS Foundation Trust
London
UK
Disclosures
PVC declares that he has no competing interests.
Richard Bliss, MB, FRCS
Consultant Endocrine Surgeon
Newcastle Upon Tyne Hospitals NHS Trust
Newcastle
UK
Disclosures
RB declares that he has no competing interests.
Haruko Akatsu, MD, MS
Clinical Associate Professor
Medical Director
Thyroid Cancer Program
Stanford University Medical Center
Stanford
CA
Disclosures
HA declares that she has no competing interests.
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