Isoechoic

Isoechoic describes tissue or a lesion that has echogenicity similar to adjacent tissues on ultrasound, resulting in comparable brightness on B-mode images. The term is relative to the surrounding tissue and depends on the acoustic interfaces and the frequency of the transducer.

Echogenicity arises from differences in acoustic impedance between tissues. When a region shares impedance with its surroundings, the reflected ultrasound echoes are alike, producing indistinct borders. Factors such as transducer frequency, gain, and patient body habitus can influence the appearance, but true isoechoic appearance reflects intrinsic similarity.

Common contexts include liver, kidney, breast, thyroid, and musculoskeletal ultrasound. For example, some benign liver lesions or focal nodular hyperplasia may be isoechoic to normal liver parenchyma; in the breast, fibroglandular tissue can be isoechoic relative to surrounding fat, complicating lesion detection.

Because isoechoic lesions blend with surrounding tissue, they may be difficult to identify on conventional B-mode imaging. Additional techniques such as Doppler ultrasound, contrast-enhanced ultrasound, elastography, or cross-sectional imaging with MRI or CT can aid characterization and help distinguish benign from malignant processes by assessing vascularity and enhancement patterns.

In practice, isoechicity is a descriptive label rather than a diagnosis. Radiologists consider isoechoic findings alongside other imaging features and clinical information to determine the need for follow-up or further investigation.