Can back-wall cystic figures of thyroid nodules predict benignity?

According to the European Thyroid Association (ETA) 2023 consensus, hyperechoic spots correspond to different subtypes: comet tail artifacts, back-wall cystic figures (BWCF), and microcalcifications. BWCF are supposed to be in favor of benignity. However, this is not well supported by the existing literature.

To assess whether EU-TIRADS 4 nodules with BWCF have a lower risk of malignancy than those without BWCF. The secondary objective was to compare this risk to that of EU-TIRADS 3 nodules and evaluate indeterminate and benign cytology rates across the three groups.

Four physicians prospectively included 150 thyroid nodules before fine-needle aspiration: 50 EU-TIRADS 4 with BWCF, 50 EU-TIRADS 4 without BWCF, and 50 EU-TIRADS 3.

The difference in malignancy risk between EU-TIRADS 4 without BWCF and EU-TIRADS 4 with BWCF was significant (P < 0.001). EU-TIRADS 3 and EU-TIRADS 4 nodules with BWCF were significantly correlated with Bethesda II cytology: 94 and 82%, respectively, compared to 26% in EU-TIRADS 4 nodules without BWCF (P < 0.001). Bethesda III-IV cytology was more frequent in EU-TIRADS 4 nodules without BWCF (62%) than in EU-TIRADS 4 with BWCF (18%) or EU-TIRADS 3 (6%) (P < 0.001).

BWCF in EU-TIRADS 4 nodules indicate a low malignancy risk, close to that of EU-TIRADS 3 nodules. These results underline the need to distinguish BWCF from other hyperechoic foci, such as microcalcifications, to improve risk stratification. Recognizing BWCF may allow the use of higher FNA thresholds and should be considered in future guidelines as I-TIRADS.