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Thyroid Follicular Carcinoma: Sonographic Features of 50 Cases

¹ Department of Radiology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905.
² Department of Endocrinology, Mayo Clinic, Rochester, MN.
³ Department of Health Sciences Research, Division of Biostatistics, Mayo Clinic, Rochester, MN.

OBJECTIVE. The purpose of our study was to retrospectively evaluate sonography of thyroid follicular neoplasms for features that would aid in distinguishing follicular carcinoma from follicular adenoma and for any imaging features that distinguish the Hürthle-cell variant of follicular carcinoma from classic follicular carcinoma.

MATERIALS AND METHODS. The study cohort consisted of patients with the diagnosis of follicular carcinoma and patients with the diagnosis of follicular adenoma. Fifty patients (25 men and 25 women; median age, 59.5 years) with a diagnosis of follicular carcinoma (27 with classic follicular carcinoma, 22 with Hürthle-cell variant of follicular carcinoma, and one insular variant) in a 6-year period were included. Fifty-two control patients (10 men and 42 women; median age, 46.5 years) were selected from a random sampling of all cases of follicular adenoma during the same time period. Sonograms were reviewed in consensus by four radiologists for various features. All study patients and control patients underwent surgical resection and pathologic analysis of their thyroid follicular neoplasm. The chi-square or Fisher's exact test was used for categorical variables; the Wilcoxon's rank sum test was used for continuous variables.

RESULTS. Hypoechoic appearance (82% of follicular carcinoma patients vs 50% of follicular adenoma patients; p < 0.005; odds ratio [OR]), 0.5; 95% CI, 0.3–0.7), absence of halo (64% of follicular carcinoma patients vs 42% of follicular adenoma patients; p < 0.05; OR, 0.4; 95% CI, 0.2–0.9), absence of cystic change (90% of follicular carcinoma patients vs 69% of follicular adenoma patients; p < 0.05; OR, 0.2; 95% CI, 0.1–0.7), greater patient age (median age of 59.5 years for follicular carcinoma patients vs 46.5 years for follicular adenoma patients; p < 0.05), size of the tumor (median size of 11.75 mL for follicular carcinoma patients vs 5.95 mL for follicular adenoma patients; p < 0.05), and male sex (50% of follicular carcinoma patients vs 19.2% of follicular adenoma patients; p < 0.005; OR, 3.7; 95% CI, 1.6–8.9) were more frequently associated with follicular thyroid cancer than with benign adenoma. No significant difference in the prevalence of refractive shadowing, echotexture, visible invasion, lymph node enlargement, adjacent nonfollicular suspicious lesions, vascularity subtype, and calcifications was observed between the two groups. Within the follicular carcinoma subgroup, homogeneous or predominantly homogeneous echotexture (67% of classic follicular carcinoma patients vs 36% of Hürthle-cell variant of follicular carcinoma patients; p < 0.05; OR, 3.5; 95% CI, 1.1–11.4) and the presence of calcifications (22% of classic follicular carcinoma patients vs 4% of Hürthle-cell variant of follicular carcinoma patients [multivariate analysis including age]; p < 0.05; OR, 22.9; 95% CI, 2.0–261.9) were associated with classic follicular carcinoma. Greater patient age (median age of 53 years for classic follicular carcinoma patients vs 64.5 years for Hürthle-cell variant of follicular carcinoma patients; p < 0.05) was associated with Hürthle-cell variant follicular carcinoma. There was no association between tumor volume, sex, sonographic halo, refractive shadowing, echogenicity, visible invasion, lymph node enlargement, adjacent nonfollicular suspicious lesions, vascularity subtype, and cystic change between the subgroups of follicular carcinoma.

CONCLUSION. The sonographic features of follicular adenoma and follicular carcinoma are very similar, but larger lesion size, lack of a sonographic halo, hypoechoic appearance, and absence of cystic change favored a follicular carcinoma diagnosis. Increased patient age and male sex are associated with malignancy. Within the follicular carcinoma subgroup, Hürthle-cell variant of follicular carcinoma is more often seen in older patients with nodules having a heterogeneous appearance and lacking internal calcifications.

Keywords: thyroid follicular adenoma • thyroid follicular carcinoma • sonography • ultrasound

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