Ultrasound uses sound waves to study the breast. Based on the same principle as radar, the sound waves are sent into the body and then reflected back to form an image on a computer screen for analysis.
What is ultrasound used for?
Ultrasound is useful in diagnosing both cancerous and benign lumps that are large enough to feel or have been detected on a mammogram. It is the best test to “rule out” the possibility of a cancer as it can distinguish whether a lump is solid (made of tissue) or a cyst (filled with water) (see Figure 1). Ultrasound can detect a simple cyst, which is non-cancerous, with 100 per cent accuracy and when this is the case, no further tests are required.
Ultrasound of a cystSometimes ultrasound is used to make a highly accurate prediction that a solid lump is cancerous, however, it is generally not used in “screening” for cancer as it usually cannot detect tiny microcalcifications that indicate early cancer.
Ultrasound is also useful for guiding radiologists in inserting a needle into a breast lump so cells can be examined under a microscope (a needle biopsy) (see Figure 2). As well, it can be used to diagnose ruptures in breast implants.
What happens during an ultrasound exam
An ultrasound is a comfortable test. While lying on a stretcher turned partway onto your side, a water-based gel is applied to the skin which may feel cool unless the gel bottle has been pre-warmed. The gel allows the probe to be easily moved over the skin in a sliding motion.
Ultrasound with a needleThe probe is placed on the breast with gentle pressure, and moved around as necessary. With larger breasts, more firm pressure is often required to flatten the tissues so that the sound waves can penetrate all the way to the back of the breast. In this way, no abnormality is overlooked.
What the results mean
When ultrasound is used to determine if a lump is present, a “negative” scan is an indication that an abnormal lump cannot be detected. Often, what feels like a lump is actually lumpy-feeling normal tissue. However, not all lumps are visible on ultrasound, so if the results are negative your situation should still be closely monitored by your family doctor.
When an abnormality is known to be present based on a mammogram, an ultrasound test can provide additional information. However, if the ultrasound is negative, this does not overrule the mammogram since some abnormalities are visible on mammography but not on ultrasound. When this happens, the radiologist must base their recommendations solely on the mammogram pictures.
Paula B. Gordon, MD