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Macrocalcifications Do Not Alter Malignancy Risk Within the American Thyroid Association Sonographic Pattern System When Present in Non-High Suspicion Thyroid Nodules.

BACKGROUND
The American Thyroid Association Sonographic Pattern System (ATASPS) depicts five levels of suspicion for malignancy based on the sonographic appearance of a thyroid nodule (1). However, 3-37% of nodules are non-classifiable (NC) when the combination of grayscale findings is not depicted by the ATASPS (1-5). The only calcifications included in the ATASPS are in solid hypoechoic high suspicion (HS) nodules and include both microcalcifications and peripheral interrupted calcifications (PIC) with soft tissue extrusion. Non-hypoechoic nodules with these and other calcification patterns, which we defined as non-high suspicion calcifications (NHSC), are not classifiable by ATASPS. We assessed the effect of assigning an ATASPS risk level to nodules with NHSC based on analysis of their other grayscale features.


METHODS
A retrospective review of 728 consecutively biopsied nodules was performed. Nodules were classified by ATASPS as high (HS), intermediate (IS), low (LS) or very low (VLS) suspicion; other nodules with patterns not described by ATASPS were non-classifiable (NC). If NC was due to NHSC, the nodule was assigned an ATASPS by analysis of grayscale features alone. Cytology and pathology results were correlated with assigned ATASPS level.


RESULTS
NC pattern was observed in 144 of the 728 nodules (20%). Of these, 101/144 (70%) had NHSC and the assigned ATASPS was IS (n=18), LS (n=62) and VLS (n=21). The distribution of cytology diagnoses within this group was similar to classifiable nodules (IS p=0.13, LS p=0.55, VLS p=0.44). The majority of NHSC (n=92, 91%) were macrocalcifications (large central or linear dystrophic calcifications); however, 9 LS pattern nodules had punctate echogenic foci (PEF), possibly representing microcalcifcations, with an estimated cancer prevalence of 19% (vs 10% for total LS group, p=0.24). The remaining NC nodules (43/144, 30%) included solid nodules with heterogeneous echogenicity (n=30) or presence of a complete circumferential rim calcification limiting further sonographic assessment(n=13). Malignancy was identified in 11/43 (26%) of these [9/30 (30%) heterogeneous solid and 2/13 (15%) with complete rim calcifications].


CONCLUSIONS
Macrocalcifications accounted for the majority of NHSC and these did not alter the expected ATASPS malignancy risk based upon grayscale features.