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]

Classification

Thyroid nodule classification

Bethesda classification system

TNM staging AJCC UICC 2017

TIRAD classification system

Based on thyroid cytopathology

For differentiated and anaplastic thyroid carcinoma

Based on sonographhic features

•Benign •Nondiagnostic or Unsatisfactory •Follicular lesion of undetermined significance •Atypia of undetermined significance •Follicular neoplasm •Suspicious for a follicular neoplasm •Malignant

Papillary, follicular, poorly differentiated, Hurthle cell and anaplastic thyroid carcinoma: •Primary tumor (T) •Regional lymph nodes (N) •Distant metastasis (M)

•TIRADS 1=Normal thyroid gland •TIRADS 2=Benign lesions •TIRADS 3=Probably benign lesions •TIRADS 4= Contain 1-4 suspicious features •TIRADS 5=Contain all five suspicious features •TIRADS 6=Biopsy proven malignancy

Bethesda System for Reporting Thyroid Cytopathology

classification	FNA cytology	Predicted risk of malignancy
Benign	Macrofollicular Adenomatoid/hyperplastic nodules Colloid adenomas (most common) Nodular goiter Lymphocytic thyroiditis Granulomatous thyroiditis	0–3 %
Nondiagnostic or Unsatisfactory		1–4 %
Follicular lesion of undetermined significance	Mixed macro- and microfollicular nodules	5–15 %
Atypia of undetermined significance	Atypical cells
Follicular neoplasm	Microfollicular nodules Hurthle cell lesions	15–30 %
Suspicious for a follicular neoplasm	Suspicious for Hurthle cell neoplasm	60–75 %
Malignant	PTC (most common) MTC Anaplastic carcinoma High-grade metastatic cancers	97–99 %

Classification of neoplastic thyroid nodules based on their origin:

		Origin	histologic subtypes	Subclass
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 Classic varient tall cell variant insular varient columnar variant Hürthle or oxyphilic variant solid or trabecular variant clear cell variant diffuse sclerosing variant cribriform morular variant hobnail variant
			follicular (11%)	Benign follicular adenoma Minimally invasive follicular carcinoma Widely invasive follicular carcinoma Encapsulated follicular variant of papillary thyroid cancer Infiltrative variant of papillary thyroid cancer
			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

Of the differentiated cancers, papillary cancer comprises about 85% of cases compared to about 10% that have follicular histology, and 3% that are Hu¨rthle cell or oxyphil tumors

Thyroid nodule classification based on the sonographhic features:

Classification system has been proposed by Horvath et al, with a modified recommendation from Jin Kwak et al.

TIRADS 1		Normal thyroid gland
TIRADS 2		Benign lesions	Avascular anechoic lesion with echogenic specks (colloid type I) vascular heteroechoic non-expansile, non-encapsulated nodules with peripheral halo (colloid type II) isoechoic or heteroechoic, non-encapsulated, expansile vascular nodules (colloid type III)	0% risk of malignancy
TIRADS 3		Probably benign lesions	Nodule property: Hyperechoic, iso-echoic or hypoechoic nodules, with partially formed capsule and peripheral vascularity, usually in setting of Hashimoto's thyroiditis (Hashimoto's pseudonodule)	<5% risk of malignancy
TIRADS 4	4a	One suspicious feature	Suspicious lesions: solid component high stiffness of nodule on elastography if available markedly hypoechoic nodule microlobulations or irregular margins microcalcifications taller-than-wider shape	5-10% risk of malignancy
	4b	Two suspicious features		10-80% risk of malignancy
	4c	Three/four suspicious features
TIRADS 5		All five suspicious features	Probably malignant lesions (more than 80% risk of malignancy)	>80% risk of malignancy
TIRADS 6		Biopsy proven malignancy