High-resolution Doppler ultrasound of the neck with both 7.5- and 12-MHz linear array transducers (Logiq 7; GE, Solingen, Germany) was performed during an outpatient visit prior to admission by a single endocrine surgeon (MB) experienced in thyroid ultrasound imaging. Thyroid volumes were calculated according to the spherical ellipsoid formula: volume = π/6 × anteroposterior diameter (cm) × width (cm) × length (cm). Fine-needle aspiration (FNA) was performed in all the patients prior to enrollment. Preoperative evaluation included serum free T3, free T4, thyroid-stimulating hormone (TSH) concentrations (respectively by commercial radioimmunoassay kits and ultrasensitive method) and serum thyroid peroxidase antibodies (TPOAb) levels.