hypoechoic

Hypoechoic is a descriptor used in diagnostic ultrasound to denote tissue or lesions that appear darker than adjacent structures on the image due to lower echogenicity. Ultrasound creates images from reflected sound waves, and echogenicity reflects how strongly a tissue reflects those waves; hypoechoic regions produce fewer echoes than surrounding tissues, while anechoic areas produce none and hyperechoic areas appear brighter.

Hypoechoic does not specify a diagnosis; it merely describes texture. Its significance depends on context, lesion margins, internal echoes, vascularity, and clinical information. The term is relative to the surrounding tissue and can vary with imaging technique and equipment settings.

Common examples occur in breast imaging, where hypoechoic masses may be benign or malignant; fibroadenomas are often hypoechoic, whereas cysts are typically anechoic. In the liver, hypoechoic lesions can represent a range of entities, including metastases or benign nodules. Normal lymph nodes may show a hypoechoic cortex with a brighter hilum. In other organs, hypoechoic areas can indicate edema, infarct, abscess, or other pathologies, again requiring correlation with clinical factors and other imaging features.

Limitations: hypoechogenicity is not specific. Definitive interpretation usually relies on additional imaging characteristics such as borders, posterior acoustic features, Doppler flow, and, when needed, biopsy or further imaging with MRI or CT. See also: anechoic, hyperechoic, echogenicity, ultrasound.