Final answer:
Neuroblastomas appear as hypoechoic mass on ultrasound (U/S). This means that the mass appears darker than the surrounding tissue on the ultrasound image.
Step-by-step explanation:
Neuroblastomas appear as hypoechoic mass on ultrasound (U/S). Hypoechoic means that the mass appears darker than the surrounding tissue on the ultrasound image. This distinction helps in identifying neuroblastomas as they are often solid tumors with dense cellular makeup.