What is the indication for surgery in a patient with a 2 cm TIRADS (Thyroid Imaging Reporting and Data System) 4 thyroid nodule?

Indication for Surgery in a 2 cm TIRADS 4 Thyroid Nodule

Bethesda type 4 (follicular neoplasm) is the indication for surgery in this patient, as follicular carcinoma cannot be distinguished from follicular adenoma on cytology alone and requires histological examination of capsular or vascular invasion for definitive diagnosis. 1, 2

Understanding the Clinical Context

For a 2 cm TIRADS 4 nodule, the first step is fine-needle aspiration (FNA) biopsy, as this size and risk category meet criteria for tissue diagnosis. 1, 2 The TIRADS 4 classification indicates intermediate-to-high suspicion based on ultrasound features, and nodules ≥1.0 cm in this category warrant FNA. 1, 2

Analysis of Each Option

Option A: Symptoms of Hyperthyroidism - NOT an Indication for Surgery

• Hyperthyroidism symptoms suggest an autonomously functioning "hot" nodule, which actually argues against malignancy with very high negative predictive value. 3
• Hot nodules on thyroid scintigraphy essentially exclude malignancy, and if confirmed as hyperfunctioning, the nodule would be managed medically with radioactive iodine rather than surgery for cancer concerns. 1, 3
• Interestingly, over 80% of hyperfunctioning nodules are classified as TIRADS 4A or higher based on ultrasound features alone, but all prove benign on histology, highlighting why functional status matters. 3

Option B: Increasing 10% in Size Over 6 Months - NOT an Indication for Surgery

• Growth alone is not an absolute indication for surgery without cytological confirmation of malignancy. 1
• While rapid growth is a concerning clinical feature, it does not bypass the need for FNA to establish tissue diagnosis before surgical planning. 1
• Guidelines emphasize that cytological confirmation via FNA is required before surgical planning for suspected malignancy. 1

Option C: Family History of Thyroid Cancer - NOT an Indication for Surgery

• Family history of thyroid cancer (particularly medullary carcinoma or familial syndromes) is a high-risk clinical factor that lowers the threshold for FNA, but does not independently indicate surgery. 1
• This factor increases suspicion and may prompt FNA in smaller nodules (<1 cm), but surgery still requires cytological or histological confirmation of malignancy. 1

Option D: Bethesda Type 4 (Follicular Neoplasm) - CORRECT INDICATION

• Bethesda IV (follicular neoplasm) with normal TSH and "cold" appearance on thyroid scan requires surgical excision for definitive diagnosis. 1
• Follicular carcinoma cannot be distinguished from follicular adenoma on cytology alone—the diagnosis requires histological examination of capsular or vascular invasion. 1, 2
• The malignancy rate in Bethesda IV nodules ranges from 12-34% depending on subcategory, making surgery necessary for definitive diagnosis. 1
• Surgery (typically thyroid lobectomy at minimum) is the only way to obtain the histological architecture needed to differentiate benign follicular adenoma from follicular carcinoma. 1

Critical Clinical Pitfalls

• Do not proceed directly to thyroidectomy without tissue diagnosis for options A, B, or C, as this may result in inappropriate surgical extent. 1
• Do not assume TIRADS classification alone determines surgical indication—the cytological result (Bethesda classification) is what drives the surgical decision. 4, 1
• Do not rely on ultrasound features to exclude malignancy in large nodules—even nodules ≥4 cm without suspicious ultrasound features carry a 20% risk of malignancy. 5
• Recognize that follicular neoplasms are the specific cytological category where FNA reaches its diagnostic limit, requiring surgical histology for definitive diagnosis. 4, 1

Recommended Management Algorithm

For this 2 cm TIRADS 4 nodule:

1. Perform ultrasound-guided FNA (already indicated based on size and TIRADS category). 1, 2
2. If Bethesda II (benign): Surveillance with repeat ultrasound at 12-24 months. 1
3. If Bethesda III (AUS/FLUS): Consider molecular testing or repeat FNA. 1
4. If Bethesda IV (follicular neoplasm): Proceed to surgery (at minimum thyroid lobectomy) for definitive diagnosis. 1
5. If Bethesda V/VI (suspicious/malignant): Refer immediately for total or near-total thyroidectomy. 1

The false-negative rate of benign cytology in nodules ≥4 cm ranges from 0-10.4% in different studies, but for a 2 cm nodule with Bethesda IV cytology, surgery remains the standard of care. 5, 6