AJR:197, December 2011 W1123 The aim of this study is to determine the usefulness of subcentimeter thyroid nod- ule evaluation. This study will compare the ultrasound features and pathologic results of subcentimeter nodules to determine the prevalence of malignancy; the correlation of various ultrasound features with malignan- cy (echo structure, echogenicity, margins, shape, calcifications, posterior acoustic shad- owing, halo, vascular pattern, and subjective suspicion); and whether a higher rate of diag- nostically suitable biopsies can be achieved with improved nodule selection, physician expertise, and on-site cytopathologic testing. Materials and Methods We retrospectively evaluated the cases of 104 consecutively registered patients (age range, 24–87 years; mean, 52.6 ± 12.5 [SD] years; men, 28 years; women, 80 years) referred to the interventional radi- ology department at our institution between March Subcentimeter Thyroid Nodules: Utility of Sonographic Characterization and Ultrasound- Guided Needle Biopsy Arjun Sharma 1 Helena Gabriel 1 Albert A. Nemcek 2 Ritu Nayar 3 Hongyang Du 4 Paul Nikolaidis 1 Sharma A, Gabriel H, Nemcek AA, Nayar R, Du H, Nikolaidis P 1 Department of Radiology, Northwestern University, Feinberg School of Medicine, 676 N St. Clair St, Ste 800, Chicago, IL 60611. Address correspondence to H. Gabriel (hgabriel@nmff.org). 2 Department of Interventional Radiology, Northwestern University, Feinberg School of Medicine, Chicago, IL. 3 Department of Pathology, Northwestern Memorial Hospital, Chicago IL. 4 Center for Clinical Research Informatics, NorthShore University HealthSystem, Evanston, IL. Neuroradiology/Head and Neck Imaging • Original Research WEB This is a Web exclusive article. AJR 2011; 197:W1123–W1128 0361–803X/11/1976–W1123 © American Roentgen Ray Society T hyroid nodules are a common medical problem found in 4–7% of patients at physical examina- tion by palpation alone, 10–67% of patients at ultrasound, and 50% at autopsy [1, 2]. Although the overall prevalence of thyroid carcinoma is 3.6% [3], the malignan- cy rate for these nodules at fine-needle aspi- ration is 9.2–14.8% [2], emphasizing the val- ue of proper risk stratification with historical, physical, and ultrasound findings. Although guidelines have been clearly outlined for management of larger thyroid nodules [4], controversy continues regarding how best to approach nodules smaller than 1 cm. Though few studies have been conduct- ed to examine the benefit of biopsy of such subcentimeter nodules, some experts suggest that a combination of suspicious ultrasound features seems to merit referral for ultra- sound-guided fine-needle aspiration. Keywords: biopsy, thyroid nodules, ultrasound DOI:10.2214/AJR.10.5684 Received August 31, 2010; accepted after revision April 28, 2011. Data from this study were presented at the 2009 annual meeting of the American Roentgen Ray Society, Boston, MA, and the 2009 annual convention of the American Institute of Ultrasound in Medicine, New York, NY. OBJECTIVE. The purpose of this study is to examine subcentimeter thyroid nodules to determine their rate of malignancy, the accuracy of various ultrasound features in prediction of malignancy, and the utility of ultrasound-guided biopsy of these nodules. MATERIALS AND METHODS. Included in this retrospective study were 104 patients in whom 108 thyroid nodules smaller than 1 cm had been biopsied. Diagnostic ultrasound examinations were reviewed, and nodules were evaluated for the following ultrasound fea- tures: internal echogenicity, margins, height-to-width ratio, presence of calcifications, poste- rior acoustic features, solid-to-cystic ratio, presence of a halo, and color Doppler character- istics. In addition, a subjective assessment of level of suspicion was assigned to each nodule. Each feature was correlated with the pathologic results to determine the accuracy of the fea- ture for predicting malignancy. RESULTS. Adequate cytologic specimens were obtained in 97 of the 108 subcentimeter biopsies (90%) performed. The average size of malignant nodules was significantly smaller than the average size of benign nodules (6.4 ± 2.1 vs 7.7 ± 1.4 mm, p = 0.041). The rate of car- cinoma among nodules with a final diagnosis was 19% (16/85). The most accurate features significantly associated with malignancy were posterior acoustic shadowing (87%), many diffuse calcifications (82%), rim calcifications (81%), and taller than wide shape (79%). The subjective level of suspicion correlated well with the presence of malignancy (76%). CONCLUSION. Subcentimeter nodules are significantly associated with the risk of ma- lignancy and can be accurately and safely biopsied with a very high diagnostic rate. Certain ultrasound features can be used to accurately stratify risk of malignancy, although no single feature replaces the clinician’s overall impression. Sharma et al. Ultrasound of Subcentimeter Thyroid Nodules Neuroradiology/Head and Neck Imaging Original Research