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Breast ultrasound is an important modality in breast imaging. It is the usual initial breast imaging modality in those under 30 years of age in many countries ref.
In assessing for malignancy, it is important to remember that one must use the most suspicious feature of three modalities (pathology, ultrasound and mammography) to guide management.
- breast ultrasound is targeted to a clinical problem
- reasonable sensitivity but poor specificity
- may have a place in screening women at high risk or with mammographically-dense breasts
- patient positioning: support elbow, flat, supine
- probe: linear array 7-13 MHz
- correct depth (skin to pectoral fascia) and correct focal zone (up to '2' is acceptable)
- dynamic range: some settings can make a cystic lesion look solid and vice versa
- scanning: radial/antiradial
- clock face with distance from nipple
- only caliper things that are real
- compression and angulation of probe from heel to toe to sharpen up the edges of a lesion
- compound imaging and resolution
- cleans up speckles
- gives between edge definition
- transmits at one frequency
- receives only multiples of this single frequency
- most noise is generated near the transducer due to reverberation
- traps for beginners
- edge refraction: from vessels, Cooper's ligaments, edge of cysts
- focal fat locules
Use of breast ultrasound
- evaluate young (usually under 30 years of age) or pregnant patients who are symptomatic
- evaluate a palpable lump with negative or equivocal mammographic findings
- detect lesions in lower contrast field
- help to distinguish between benign vs malignant characteristics
- guiding biopsy
- evaluate breast implants for rupture
See main article on breast cysts:
- edge is the most important feature
- no rind
- pencil thin
- well-defined all the way around
- is it compressible?
- can you move the inside?
- is there a solid edge: sometimes color Doppler will help
Power Doppler and vocal fremitus
- to help distinguish malignant from benign tumors
- get patient to say "ahhh" or "99" very loud and observe the center of the lesion:
- cancer - vibrations conducted along tumor infiltration into center, hence color pixels run into center of tumor and fill it in
- benign lesions (e.g. fat lobules) - cannot get power Doppler into center of lesion
- not a useful test in superficial lesions or large breasts
Features that are found not to be useful in differentiating malignant from benign lesions
- heterogeneity/homogeneity of texture
- normal/enhanced through transmission, e.g. mucinous cancers
- being iso-mildly hypoechoic
- maximum diameter
Classification of nodules
- benign: no malignant features, combinations of benign findings
- indeterminate: no malignant findings; no combination of benign findings (needs biopsy)
- malignant: one malignant feature (needs biopsy)
Potential pitfalls in breast ultrasound in practice
Always correlate the mammogram images before the ultrasound is done. The operator must know where the lesion is located in the breast and the nature of the lesion. What are you looking for and where is it located?
If you work with ultrasound technologists, review by the radiologist in real time is almost always required unless for the simplest of overtly benign breast pathology. In everyday practice, do not be tempted to review static images of breast pathology without looking in real time. This is a very significant potential pitfall for the misdiagnosis of breast pathology.
With the high resolution of the newest apparatus, consider doing ultrasound even if you are working up microcalcifications. In cases where you find them on ultrasound, you may be able to supply a tissue diagnosis and save the inconvenience of mammotome biopsy for the patient.
With greater emphasis now being placed on characterizing breast density, more authors feel there is a place for screening ultrasound in the dense (>75%) breast. In Connecticut, ultrasound of the dense breast is now mandated and paid for by the state. There is good evidence that in this group of patients the yield of ultrasound in picking up cancers is almost as high as mammography itself in the range of an additional 3-4/1000 cancers found (Berg, ECR, 2013). In the context of screening for breast cancer, ultrasound in capable hands will find low grade DCIS that may not be visible on mammography. "Second look" ultrasound after breast MRI will yield a positive finding in about 56% of cases.
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