Articles
Register for Sonography of the Breast
by Cynthia L. Rapp BS, RDMS
Radiology Imaging Associates - Swedish Medical Center
Englewood, Colorado
Reprinted with author's permission.
Positioning
The patient is positioned in a supine position with the ipsilateral hand raised above the head. The patient is rolled into a contra-lateral posterior oblique position to a degree, which minimizes breast thickness in the quadrant being scanned. Lesions in the medial quadrants may be scanned in a straight supine position. Lesions in the lateral quadrants require the greatest degree of obliquity. Generally, greater degrees of obliquity are required for larger breasts.
This positioning accomplishes two things:
-
First, the breast is thinned to the greatest extent possible, so that the high frequency, near-field probes used, has adequately penetrate to the chest wall and the focusing characteristics of the probe are optimized.
-
Secondly, the tissue planes of the breast, which are conical in the upright and prone positions, are pulled into a plane, which is parallel to the skin line. This minimizes critical angle shadowing and improves penetration and prevents degradation of focusing characteristics.
Scan Plane – Radial and Anti-radial
All solid lesions should be scanned in the plane of the ductal system (radial and anti-radial) in order to demonstrate subtle projections that course towards the nipple or branch outward in the breast.
If a nodule is scanned only in the conventional method of longitudinal and transverse, these subtle findings may be missed, and the lesion may appear spheroid or ellipsoid, and be misclassified as probably benign.
System Optimization
Ensure that your system is optimized for breast imaging before starting your scan. If the gain is not set correctly, solid lesions can look cystic or a cyst look solid. Before starting to scan the area of interest, find an area in the breast with fatty tissue. Most patients have some fat, usually in the inner aspect of the breast. Set your gain so the fat is medium gray.
Compare all lesions in the breast to fat. If the gain is set correctly and fat is medium gray, glandular tissue and most benign lesions, such as fibroadenomas, appear isoechoic to mildly hypoechoic compared to fat. Malignant lesions can be mildly hypoechoic to markedly hypoechoic and cysts are markedly hypoechoic to anechoic compared to fat. The structures that are hyperechoic compared to fat are skin, fibrous tissue and calcifications.
Mammographic vs. Sonographic
Correlation
When the main indication for breast ultrasound is a palpable lump, it is imperative that the lump be palpated while scanning. A breast biopsy can be avoided if it can be shown that the lump is due to a simple cyst or normal fibroglandular tissue. Both can cause palpable lumps. Simple cysts are so common in some age groups that they are virtually a variant of normal. Fibroglandular tissue is present in at least some part of the breast, in the majority of all women -- especially those who are within the reproductive years and even in postmenopausal women who are undergoing hormonal replacement therapy
When the main indication for breast ultrasound is a mammographic nodule, mass, or focal asymmetrical density, it is essential that size, shape, location, and density of surrounding tissues are the same on mammograms and ultrasound. As for the palpable lumps, merely showing a simple cyst or focal collection of fibroglandular tissues does not prove that either is the cause of the mammographic abnormality. Either could easily be an incidental finding, especially if the breasts are mammographically dense or if there are multiple mammographic densities. Only if the size, shape, location, and density of surrounding tissues are similar on mammography and sonography, are we sure that a simple cyst or fibrous pseudo-tumor is the cause of the mammographic density
When correlating breast ultrasound with mammography, one should compare the CC view of the mammogram with the transverse view on ultrasound. The shape of a mammographic lesion will be easier to reproduce sonographically if the scan plane is identical to the projection plane of the mammogram. The MLO view of the mammogram may vary from 30o to 60o. It is difficult to reproduce the exact degree of obliquity on the ultrasound that was used on the MLO view of the mammogram.
Normal
Sonographic Anatomy
The skin is hyperechoic and approximately 2mm thick. The subcutaneous fat is seen anterior to the pre-mammary fascia. Cooper’s ligaments may be seen as hyperechoic bands coursing through the subcutaneous fat. The mammary zone is where the majority of breast cancers, detectable by ultrasound, are located. Posterior to the mammary zone is the retro-mammary fascia and fat. And the most posterior structure is the pectoralis muscle and then the lung.
Continue to page 3
