What are the characteristics of a follicular neoplasm of the thyroid?

From the Guidelines

Follicular neoplasm of the thyroid is a diagnostic category that requires surgical removal of the affected thyroid lobe for definitive diagnosis, as microscopic examination of the entire nodule is necessary to identify capsular or vascular invasion that would indicate cancer. The characteristics of a follicular neoplasm of the thyroid include thyroid cells arranged in follicular patterns, but the lesion cannot be definitively determined as benign or malignant through fine needle aspiration (FNA) biopsy alone 1. Some key points to consider in the diagnosis and treatment of follicular neoplasm of the thyroid include:

• Surgical removal of the affected thyroid lobe (lobectomy) is recommended for definitive diagnosis 1
• Prior to surgery, patients should undergo thyroid function tests and ultrasound imaging to assess nodule characteristics 1
• If malignancy is confirmed after surgery, treatment may include completion thyroidectomy, radioactive iodine therapy, and thyroid hormone replacement with levothyroxine 1
• Patients require lifelong monitoring with thyroid function tests every 6-12 months 1
• The distinction between benign follicular adenoma and malignant follicular carcinoma is important because follicular carcinomas can spread through the bloodstream to bones, lungs, and other organs, though they generally have a good prognosis with appropriate treatment 1
• Approximately 15-30% of follicular neoplasms are ultimately diagnosed as cancer 1 It is essential to note that the treatment and management of follicular neoplasm of the thyroid should be individualized based on the patient's specific condition and characteristics of the nodule, as outlined in the NCCN Guidelines for Thyroid Carcinoma 1.

From the Research

Characteristics of Follicular Neoplasms

• Follicular neoplasms of the thyroid are usually diagnosed following fine-needle aspiration (FNA) biopsy of a dominant thyroid nodule 2
• An FNA diagnosis of a follicular neoplasm represents a heterogeneous group of lesions including benign follicular hyperplasia, follicular adenomas, follicular carcinomas, and the follicular variant of papillary carcinoma 2
• Hürthle cell neoplasms are also often included in this group 2

Diagnostic Challenges

• Follicular thyroid carcinoma cannot be distinguished reliably from benign follicular neoplasia by fine needle aspiration (FNA) biopsy 3
• The criteria for malignancy in both follicular and Hürthle cell neoplasms requires vascular or capsular invasion seen on permanent histology 2
• Intraoperative frozen section analysis of follicular neoplasms rarely renders informative information 2, 4

Predictive Factors of Malignancy

• A high serum thyroglobulin (Tg) level (≥75 ng/mL) and calcification are significant predictive factors for malignancy in case of follicular neoplasm 5
• Hard lesions to palpation, solitary, and hypoechoic follicular neoplasms by ultrasound show elevated risks of malignancy 6
• Previously suggested factors with elevated risk for malignancy such as extremes of age, male gender, and large nodule size were not associated with increased risk 6

Treatment and Outcome

• Approximately 20% of follicular neoplasms prove to be malignant 3, 2
• For lesions greater than 1.0 cm in size, the majority of surgeons and endocrinologists recommend a total thyroidectomy 2
• Postoperative treatment generally includes therapeutic doses of 131I for follicular carcinomas 2
• The preferred treatment for follicular neoplasms is lobectomy followed by completion total thyroidectomy for histologically proven carcinomas larger than 1.0 cm 4