The term hypoechoic is used in ultrasonography and refers to a mass that reflects a reduced number of ultrasound waves. A hypoechoic mass appears darker than other masses on an ultrasound scan.
The term hypoechoic comes from Ancient Greek and it literally means "giving off few echoes". According to the McGraw-Hill Concise Dictionary of Modern Medicine, this type of mass is abnormal and is often due to pathologic changes in the density of tissues. The simple apparition of a hypoechoic mass on an ultrasound is not enough for a diagnosis. Further tests including biopsies are required to establish the exact origin of the mass.