Collapsing benign cystic nodules of the thyroid gland: sonographic differentiation from papillary thyroid carcinoma

Abstract

Background and purpose: The US features of benign and malignant nodules overlap, and benign thyroid lesions can mimic thyroid malignancy on US. Benign cystic nodules after spontaneous collapse or needle aspiration, can mimic malignant thyroid nodules. Our aim was to evaluate the US features of CBCNs of the thyroid that distinguish such nodules from malignant thyroid nodules.

Materials and methods: US and clinical findings in 13 patients, each with a single CBCN, were evaluated to determine if they showed >50% cystic content on initial US or CT and >30% decrease in maximum diameter on follow-up US. We compared these findings with those of 26 patients, each with a single surgically confirmed PTMC. US scans were analyzed for internal content, shape, margin, echogenicity, presence of echogenic dots suggesting micro- and macrocalcification, inner isoechoic rim, and low-echoic halo.

Results: Six of the 13 (46%) CBCNs were classified as malignant on US due to their marked hypoechogenicity, microcalcification, or spiculated margins. US features that differed between CBCNs and PTMCs were shape (ovoid-to-round versus taller-than-wide, P = .016); margins (ill-defined versus spiculated, P < .000); low-echoic halo (P < .000); inner isoechoic rim (P < .000) with high negative predictive values (100%, 91%, 91%, and 89%, respectively); and clinically acceptable diagnostic accuracy (59%, 80%, 82%, and 85%, respectively).

Conclusions: US features helpful for differential diagnosis of CBCNs from PTMCs include shape, margin, and the presence of an inner isoechoic rim and a low-echoic halo. Familiarity with US features suggesting CBCNs may be helpful in reducing unnecessary repeated FNABs.

Fig 1.

A 59-year-old woman with a CBCN. A routine transverse US shows a 0.8-cm-long round hypoechoic nodule, with a peripheral low-echoic halo (arrowheads) and an inner isoechoic rim (arrows). Subsequent pathologic examination after surgery confirmed degenerating nodular hyperplasia in the left thyroid gland and papillary carcinoma in the right thyroid gland (not shown).

Fig 2.

A 68-year-old man with a collapsing benign cystic nodule. A, A transverse US of the thyroid gland shows a 0.6-cm-long ill-defined ovoid markedly hypoechoic nodule with suspicious microcalcification. Note a low-echoic halo and an inner isoechoic rim (arrowheads) surrounding the nodule. B, A transverse US performed 1 year ago reveals a 1.7-cm-long predominantly cystic nodule with an isoechoic solid component at the same location.

Fig 3.

A 42-year-old woman with papillary thyroid carcinoma. Transverse sonogram shows a 0.6-cm-long spiculated taller-than-wide hypoechoic nodule (arrows) within the right lobe of the thyroid gland, which is suspicious for malignancy by US criteria. Note there is neither a low-echoic halo nor an inner isoechoic rim at the periphery. Subsequent cytologic and histologic examination confirmed the diagnosis of papillary thyroid carcinoma.