What exactly is an ultrasound? How does it work? And why does my doctor want me to have one? Everything you need to know about breast ultrasound: the what, how, and why of this common screening device.

Q. I went for my regular mammogram, and I got a callback for another view. Now they want to do an ultrasound. What does that mean? I’m scared…

A. First of all, it’s natural to be scared when everything doesn’t go as usual with your annual mammogram. About 10% to 15% of all screening mammograms result in a “callback” – the need for a further mammogram. And about 95% of callbacks end right there, with no further screening necessary. The radiologist might have seen a piece of breast tissue folded over on itself, regular glandular tissue viewed from an odd angle, or something else that, with another, different mammogram, looks just fine.

But sometimes, even after a second view, something doesn’t look quite right. At that point, the radiologist may order an ultrasound, a.k.a. sonogram.

Q. So, is the ultrasound likely to show something serious? Does this mean I have cancer?

A. No, not at all. The vast majority of breast lumps, or “abnormalities” seen on mammograms, are NOT cancer. Even if the ultrasound were to prove inconclusive and you needed a biopsy, about 85% of biopsies are negative; no cancer. So odds are your ultrasound will show that what the radiologist saw is NOT cancer.

Q. What kinds of things can an ultrasound show?

A. The ultrasound’s main advantage over mammograms is that it’s very good at showing whether a lump or mass is solid, or filled with fluid. A solid lump needs further examination, either via MRI, or biopsy. But if the lump is filled with fluid, your testing is done: the lump is a cyst.

Cysts (and accompanying fibrocystic change) are quite prevalent in women under the age of 50. In fact, the most common cause of non-cancerous breast lumps in women between the ages of 30 and 50 is cysts. On an ultrasound, a cyst is dark black outlined in white; it’s very distinctive, and easily identified.

An ultrasound might also show a plugged milk duct, or a fat lobule, other conditions mammograms are unable to distinguish from regular breast tissue. 

Q. Well, I feel better knowing that I’m more likely to have a cyst than cancer. I’m still worried, though. What’s the test like?

A. An ultrasound can take 20 to 30 minutes, but it’s an easy test. You’ll lie on a table with your arm above your head, and the person performing the ultrasound (the sonographer) will rub a clear, water-based gel on your breast; sometimes it feels uncomfortably cold for a minute, but it warms up fast.

The sonographer will run a small device, called a transducer, over the area of your breast with the lump. The gel helps the transducer maintain contact with your skin. The transducer sends images to a computer screen, which the sonographer watches as s/he works. Since this is all done in real time, s/he can easily adjust the area being scanned to view the lump from different angles.