A nodule is a small, discrete lesion or abnormal tissue, commonly defined as being less than 10 millimeters in diameter, though definitions vary by context and organ system. Nodules can occur in many organs including the thyroid, liver, lung, breast, and adrenal glands. On ultrasound, nodules appear as focal areas of abnormal echogenicity compared to surrounding tissue. Thyroid nodules are among the most commonly encountered incidental findings, and their ultrasound characteristics determine the need for further workup or biopsy using standardized classification systems. Liver nodules may represent benign lesions, regenerative nodules in cirrhosis, or malignancy depending on their appearance, size, and clinical context. Systematic description of nodule characteristics, including size, echogenicity, margins, and vascularity, is fundamental to ultrasound reporting.
Sonography Term