Fine needle aspiration (FNA) of thyroid nodules and enlarged lymph nodes is a vital diagnostic tool that is safe and reliable with side effects very uncommon. Direct, real-time ultrasound (US) guidance is used to improve accuracy in punctuating the nodule. The tip of the needle is seen as a very bright spot and must be within the nodule during aspiration. The specimen is then examined by a pathologist according to the Bethesda System for Reporting Thyroid Cytology – see below.
It is not obvious which nodule in a goiter to biopsy. Guidelines include:
history of head and neck irradiation in youth
family history of medullary or papillary thyroid cancer
unusual firmness without calcification
growth of nodule
enlarged lymph nodes
Ultrasonic features (at least two):
hypoechoic nodule with one of the following: irregular / blurred margins, central vascularity, microcalcifications, taller rather than wide shape, enlargement compared to prior examinations
Biopsy a “suspicious” nodule rather than the largest one
The size and number of nodules do not correlate directly with risk factors.
There is limited ability to aspirate a nodule or node even with ultrasound guidenance. Diagnostic yield is usually not higher than 85% for nodules 10mm or larger. To improve accuracy of FNA as well as for safety reasons it is advisable to discontinue antiplatelet and anticoagulant medication prior to biopsy. In case FNA is not diagnostic it should be repeated after a period of time. When growth of a nodule or emergence of adenopathy is observed or symptoms appear that suggest pressure on cervical structures FNA should be repeated even after previous benign result.
To address the terminology and other issues related to thyroid FNA, the National Cancer Institute (NCI) hosted the “the NCI Thyroid Fine Needle Aspiration State of the Science conference” in 2007 at Bethesda, Maryland. The conclusions of the meeting led to the Bethesda Thyroid Atlas Project and formed the framework for The Bethesda System for Reporting Thyroid Cytology (TBSRTC).
These are the recommended diagnostic categories and management:
I - Nondiagnostic or unsatisfactory - cystic fluid only, virtually acellular specimen, other like obscuring blood, collecting artifacts, etc.
II – Benign - consistent with a benign follicular nodule (includes adenomatoid nodule, colloid nodule etc.), lymphocytic (Hashimoto) thyroiditis in the proper clinical context, granulomatous (subacute) thyroiditis, and other
III - Atypia of undetermined significance or follicular lesion of undetermined significance
IV - Follicular neoplasm or suspicious for a follicular neoplasm, specify if Hurthle cell (oncocytic type)
V - Suspicious for malignancy: papillary carcinoma, medullary carcinoma, metastatic carcinoma, lymphoma, other
VI – Malignant: papillary thyroid carcinoma, poorly differentiated carcinoma, medullary thyroid carcinoma, undifferentiated (anaplastic) carcinoma, squamous cell carcinoma, carcinoma with mixed features (specify), metastatic carcinoma, non-Hodgkin’s lymphoma, other
|Diagnostic category||Risk of malignancy (%)||Usual management|
|I. Nondiagnostic or unsatisfactory||1-4||Repeat FNA with ultrasound guidance|
|II. Benign||0-3||Clinical follow-up|
|III. Atypia of undetermined significance or follicular lesion of undetermined significance||5-15||Repeat FNA|
|IV. Follicular neoplasm or suspicious for follicular neoplasm||15-30||Surgical lobectomy|
|V. Suspicious for malignancy||60-75||Near-total thyroidectomy or surgical lobectomy|
|VI. Malignant||97-99||Near-total thyroidectomy|