Clinical significance of acoustic shadowing without high-echo signal in papillary thyroid microcarcinoma

Papillary thyroid microcarcinoma (PTMC) with acoustic shadowing without a high-echo signal is occasionally encountered in clinical practice. However, the pathophysiology underlying such findings has not been investigated. We aimed to elucidate the clinical significance of acoustic shadowing without a high-echo signal in PTMC.

Nine PTMC nodules with acoustic shadowing but no high-echo signal and 76 PTMC nodules without acoustic shadowing or high-echo signal were included. Nodules were analyzed using ultrasound, aspiration cytology, and histological examination.

Punctate echogenic foci were not observed in PTMC nodules with acoustic shadowing but no high-echo signals. The frequency (11.1%) of psammoma bodies in PTMC nodules with acoustic shadowing was lower than that in nodules without acoustic shadowing (31.6%); however, the difference was not significant. Extensive hyalinization was observed in 66.7% and 3.9% of PTMC nodules with and without acoustic shadowing, respectively (p < 0.001). The distributions of acoustic shadowing and hyalinized stroma were correlated.

Acoustic shadowing without a high-echo signal is caused not by calcification but rather by extensive hyalinization. Our results may help refine the sonographic criteria for PTMC and provide a novel imaging marker for identifying indolent tumors, thereby supporting active surveillance strategies and potentially reducing overtreatment.