What is the best diagnostic test to distinguish between a liquid-filled cyst and a solid mass in the breast?

Ultrasound is the most effective diagnostic test for distinguishing between a liquid-filled cyst and a solid mass in the breast. This imaging technique uses sound waves to create images of soft tissues, allowing healthcare providers to assess the characteristics of breast lesions with great clarity.

One of the main advantages of ultrasound is its ability to determine whether a breast mass is fluid-filled, which will appear anechoic (dark) on the ultrasound image, or solid, which will typically appear echogenic (lighter). These distinct visual characteristics enable radiologists to differentiate between benign cysts, which are usually non-threatening, and solid masses that may require further investigation.

Mammography is beneficial for detecting breast abnormalities but may not provide sufficient detail to differentiate between cysts and solid masses due to its two-dimensional nature. Biopsy, while definitive in characterizing tissue, is an invasive procedure that is usually performed after other imaging modalities suggest the presence of a concerning lesion. Ductoscopy is a specialized technique used primarily for investigating discharge from the nipples and is not typically used as a first-line imaging method for distinguishing between cysts and solid masses.