Thyroid nodule classification
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mahshid Mir, M.D. [2]
Bethesda System for Reporting Thyroid Cytopathology
- 19888858
| classification | FNA cytology | Predicted risk of malignancy |
|---|---|---|
| Benign |
|
0–3 % |
| Follicular lesion of undetermined significance |
|
5–15 % |
| Atypia of undetermined significance |
| |
| Follicular neoplasm |
|
15–30 % |
| Suspicious for a follicular neoplasm |
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| Malignant |
|
97–99 % |
The risk of malignancy development based on the FNA result in case of indefinite diagnosis are as below:
- Nondiagnostic or Unsatisfactory: 1–4 % predicted risk of malignancy.
- Suspicious for malignancy: 60–75 % predicted risk of malignancy
Thyroid carcinomas are classified according to the cell type from which they develop
Classification of neoplastic thyroid nodules based on their origin:
| Origin | histologic subtypes | |||
|---|---|---|---|---|
| Nonmedullary thyroid cancers (NMTCs) | 95% of tumors | thyroid epithelial cells | papillary (85%) | 95% are sporadic tumors
5% may be related to inherited genetics due to familial origin |
| follicular (11%) | ||||
| Hürthle cell (3%) | ||||
| anaplastic (1%) | ||||
| Medullary thyroid cancers (MTCs) | 5% of all thyroid malignancies | calcitonin-producing parafollicular cells | 20% they are familial and occur as part of the multiple endocrine neoplasia (MEN) syndromes |
| Follicular thyroid lesions | Benign follicular adenoma | ||
| Minimally invasive follicular carcinoma | |||
| Widely invasive follicular carcinoma | |||
| Encapsulated follicular variant of papillary thyroid cancer | |||
| Infiltrative variant of papillary thyroid cancer | |||
| Classic varient | |||
| papillary thyroid cancer | tall cell variant | more aggressive tumor than classical papillary cancer
tumor cells with eosinophilic cytoplasm that are twice as tall as they are wide. The primary tumors tend to be large, they are often invasive, and many patients have both local and distant metastases at the time of diagnosis |
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| insular varient | solid nests of tumor, often separated by fibrous bands, but the tumor cell nuclei have the same characteristics as do the nuclei of classical papillary cancers. | ||
| columnar variant | elongated cells with palisading nuclei. | ||
| Hürthle or oxyphilic variant | Cellular features of Hürthle cell carcinomas but cells that are arranged in papillary formations. | ||
| solid or trabecular variant | |||
| clear cell variant | must be distinguished from clear cell carcinomas of other organs such as the kidney or colon that have metastasized to the thyroid. | ||
| diffuse sclerosing variant | diffuse involvement of the thyroid, stromal fibrosis, and prominent lymphocytic infiltration | ||
| cribriform morular variant | Prominent cribriform pattern with solid and spindle cell areas as well as squamous morules. This variant is often associated with familial adenomatous polyposis. | ||
| hobnail variant | harbors BRAF V600E mutations and appears to be associated with a high risk of distant metastases and an increased disease-specific mortality |