What is the next step if a CT (Computed Tomography) scan shows a 5 mm calcified area in the posterior interpolar right thyroid lobe?

Management of a 5 mm Calcified Area in the Posterior Interpolar Right Thyroid Lobe

Ultrasound-guided fine needle aspiration (FNA) should be the next step in the management of a 5 mm calcified area in the posterior interpolar right thyroid lobe detected on CT soft tissue imaging. 1, 2

Risk Assessment of Thyroid Calcifications

• Thyroid calcifications are associated with a significantly higher risk of malignancy, with studies showing that 59.2% of patients with intrathyroidal calcification were found to have thyroid carcinoma 1
• Calcifications in thyroid nodules are classified according to their diameter and location, with microcalcifications (≤1 mm) generally considered more suspicious for malignancy than macrocalcifications (>1 mm) 3
• The presence of calcification in a solitary thyroid nodule carries a particularly high risk of malignancy (75.7% in one study), warranting thorough evaluation regardless of size 1

Diagnostic Algorithm

1. Ultrasound evaluation:

   • Ultrasound is the preferred next imaging modality to better characterize the calcified area and assess for additional thyroid nodules 4
   • Ultrasound can help classify the calcification pattern (microcalcification, macrocalcification, rim calcification, or isolated calcification) which has implications for malignancy risk 2, 5

2. Ultrasound-guided FNA:

   • For a 5 mm calcified area in the thyroid, ultrasound-guided FNA is recommended to obtain tissue diagnosis 4
   • Even though the nodule is small (5 mm), the presence of calcification increases suspicion for malignancy, justifying FNA despite being below the typical 1 cm threshold 4, 1

3. Laboratory assessment:

   • Measure serum TSH to evaluate thyroid function as part of the comprehensive evaluation 4

Interpretation of FNA Results

• If FNA is benign (Bethesda II), follow-up with ultrasound in 6-12 months is recommended 4
• If FNA is indeterminate (Bethesda III or IV), consider molecular testing to assist in diagnosis 4
• If FNA is suspicious or positive for malignancy (Bethesda V or VI), surgical management should be considered 4

Important Considerations

• CT is optimal for characterizing soft-tissue calcification but has limitations in fully evaluating thyroid nodules compared to ultrasound 6
• The diagnostic value of calcification patterns varies, with microcalcifications having higher specificity (93.6%) but limited sensitivity (33.7%) for predicting malignancy 5
• CT features of thyroid nodules with calcifications can provide additional information, with central calcifications being more common than rim calcifications in nodules with isolated macrocalcifications 7

Potential Pitfalls

• Relying solely on the presence of calcification for diagnosis may lead to unnecessary procedures, as calcifications can occur in both benign and malignant thyroid disease 1, 5
• Some studies report that up to 24.1% of patients with calcified thyroid nodules that proved to be malignant had preoperative FNA results reported as benign, highlighting the importance of considering clinical and imaging features in addition to FNA results 1
• The mechanism of calcification formation in thyroid nodules is still poorly understood, involving molecules such as RUNX-2, SPARC, ALP, BSP, and osteopontin 3