Thyroid & Adrenal
On USG of thyroid which is not S/o malignancy
Ultrasound features of thyroid nodules
a. Echogenicity The incidence of malignancy is 4% when a solid thyroid nodule is hyperechoic. If the lesion is hypoechoic, the incidence of malignancy rises to 26%. However, hypoechogenicity alone is inaccurate in predicting malignancy, and if used as a sole predictive sign, it has a relatively poor specificity (49%) and positive predictive value (40%).
b. Margins A malignant thyroid nodule tends to have ill-defined margins on ultrasound. A peripheral halo of decreased echogenicity is seen around hypoechoic and isoechoic nodules and is caused by either the capsule of the nodule or compressed thyroid tissue and vessels. The absence of a halo has a specificity of 77% and sensitivity of 67% in predicting malignancy.
c. Calcification: Fine punctate calcification due to calcified psammoma bodies within the nodule is seen in papillary carcinoma in 25%–40% of cases. If used as the sole predictive sign of malignancy, microcalcification is the most reliable one with an accuracy of 76%, specificity of 93% and a positive predictive value of 70%. Coarse, dysmorphic or curvilinear calcifications commonly indicate benignity.
d. Comet tail sign The presence of a comet tail sign in a thyroid nodule indicates the presence of colloid within a benign colloid nodule and is a strong predictor of benignity.
e. Solid/cystic Thyroid nodules with large cystic components are usually benign nodules that have undergone cystic degeneration or haemorrhage. However, papillary carcinoma occasionally demonstrates a cystic component and may mimic a benign nodule, though the presence of punctate calcification within the solid component helps in its identification.
7. Colour flow patterns There are three patterns of vascular distribution within a thyroid nodule:
a. –Type I: complete absence of flow signal within the nodule
b. –Type II: exclusive perinodular flow signals
c. –Type III: intranodular flow with multiple vascular poles chaotically arranged, with or without significant perinodular vessels.
i. Type III pattern is generally associated with malignancy.
ii. Types I and II are more commonly seen in benign hyperplastic nodules.