Follicular Thyroid Neoplasm (TI-RADS 4, Bethesda IV)

Ultrasound

Female patient, 33 years old, presented for an ultrasound examination of the thyroid gland. The medical history revealed a previously identified thyroid nodule.

At the junction of the right lobe and isthmus of the thyroid gland, an oval, wider-than-tall nodule with mixed echogenicity is visualized, containing several small anechoic cystic components, measuring 10.5 × 4 mm.
Color Doppler imaging demonstrates mixed vascularity. The lesion corresponds to TI-RADS 4.

Ultrasound demonstrates a thyroid nodule at the junction of the right lobe and isthmus — TI-RADS 4.

Fine-needle aspiration biopsy of the thyroid nodule was performed under ultrasound guidance.
The specimen contains cohesive and follicular-like groups of thyrocytes with rounded hyperchromatic nuclei and scant cytoplasm.
The cytological findings are consistent with a follicular thyroid neoplasm.
According to the Bethesda System — Category IV.

Bethesda IV (follicular neoplasm) is not always cancer.
On the other hand, TI-RADS allows estimation of the risk of malignancy based on the ultrasound appearance of a thyroid nodule; however, it does not provide definitive morphological diagnosis.
When fine-needle aspiration biopsy yields Bethesda IV (“follicular neoplasm / suspicious for a follicular neoplasm”), this category includes both follicular adenoma and follicular carcinoma, and cytological examination alone cannot reliably distinguish between these entities.
The definitive diagnosis of malignancy is based on the identification of capsular and/or vascular invasion, which requires histopathological examination of the resected lesion.
Thus, the combination of an ultrasound category of TI-RADS 4 and a cytological category of Bethesda IV requires further assessment and appropriate management rather than being interpreted as definitive confirmation of a malignant neoplasm.

Follicular thyroid neoplasm