In this radiology lecture, we review the ultrasound appearance of Hashimoto’s thyroiditis with three unique cases! Key teaching points include: * Normal thyroid gland isthmus measures less than 0.4 cm, transverse and AP lobe diameters measure less than 2 cm. * Hashimoto’s thyroiditis is an autoimmune thyroiditis caused by antibodies to thyroid proteins. * Most common in middle-aged females. * May coexist with other autoimmune disorders: Lupus, rheumatoid arthritis. * AKA chronic autoimmune lymphocytic thyroiditis: Gland is infiltrated with lymphocytes and plasma cells, fibrotic reaction replaces normal parenchyma. * Leads to hypothyroidism = Most common cause in USA. * Increased risk of thyroid cancer, including thyroid lymphoma. * On ultrasound, gland is normal-sized or enlarged in initial phase with heterogeneously hypoechoic parenchymal echotexture. * May have hypoechoic micronodules (1-6 mm) yielding a “pseudonodular” or “giraffe” pattern = High positive predictive value. * Can also present with thin echogenic fibrous strands, lobulated contour, and geographic hypoechogenicity without discrete nodules. * Gland may be atrophic in chronic cases. * Variable color Doppler flow, may be hypervascular. * Reactive, morphologically-normal neck nodes may be present. * Can be difficult to differentiate from other forms of thyroiditis on ultrasound. * Laboratory/serologic diagnosis: Thyroid function tests (TSH, free T4 test), thyroid peroxidase (TPO) antibodies present in most (95%) patients, and antithyroglobulin antibodies. * Treatment: Thyroid hormone replacement if hypothyroid. To learn more about the Samsung RS85 Prestige ultrasound system, please visit: https://www.bostonimaging.com/rs85-prestige-ultrasound-system-4 Click the YouTube Community tab or follow on social media for bonus teaching material posted throughout the week! Instagram: https://www.instagram.com/radiologistHQ/ Facebook: https://www.facebook.com/radiologistHeadQuarters/ Twitter: https://twitter.com/radiologistHQ Reddit: https://www.reddit.com/user/radiologistHQ/