Diagnostic ultrasound ( PDFDrive )

CHAPTER 21 The Breast 767
involve internal mammary lymph nodes in the second and third
interspaces. Using color Doppler sonography to identify the
internal mammary vessels can be helpful in inding abnormal
internal mammary lymph nodes. Normal internal mammary
lymph nodes can be identiied under ideal circumstances, but
not in all patients.
A signiicant percentage of patients have lymph nodes that
lie within the breast and are called intramammary lymph nodes.
hese can lie anywhere within the breast but are most common
in the axillary segment just below the axilla. hey usually lie
within a centimeter of the posterior mammary artery, a branch
of the axillary artery that extends from the axilla toward the
nipple. Intramammary lymph nodes can also be found occasionally
in the medial edge of the breast supericial to the internal
mammary lymph nodes. hese medial lymph nodes are seen
much less frequently on mammography than on sonography
because mammographic compression can seldom pull them far
3
2
Pec minor
Pec major
FIG. 21.10 Pectoralis Minor Muscle and Levels of Axillary Lymph
Nodes. Extended–ield-of-view (FOV) sonogram shows metastases to
all three axillary lymph node levels on the left. The level of axillary lymph
nodes is determined by the pectoralis minor muscle. Lymph nodes that
lie inferior and lateral to the inferolateral edge of the pectoralis minor
muscle are level 1 nodes; those that lie deep to the pectoralis minor
muscle are level 2 lymph nodes; and those that lie superior and medial
to the superomedial edge of the pectoralis minor muscles are level 3
(infraclavicular) lymph nodes.
2
OBL LT AX LNS
1
enough away from the chest wall to be mammographically visible.
Medial intramammary lymph nodes can be diicult to demonstrate
sonographically without the use of an acoustic standof
because of their supericial location just beneath the skin.
Breast cancer metastases can involve the supraclavicular
lymph nodes, but these nodes are positive only when
lymph node metastases are extensive. Metastases oten involve
levels 1, 2, and 3 axillary lymph nodes or internal mammary
and internal jugular lymph nodes before reaching the supraclavicular
nodes.
he irst lymph node to which lymphatic drainage lows and
the irst node involved by metastases has been termed the sentinel
lymph node. he location of the sentinel node varies, depending
on the location of the primary tumor within the breast. he
sentinel lymph node is usually a level 1 axillary lymph node, but
in certain cases it may be an intramammary node or even a level
2 node. Occasionally the sentinel node may be an internal
mammary node.
SONOGRAPHIC EQUIPMENT
Breast ultrasound requires high-frequency transducers that
are optimized for near-ield imaging. Transducers used for
breast sonography should be high-resolution, real-time, lineararray,
broad-bandwidth transducers operating at a center frequency
of at least 12 MHz and preferably higher. Other transducers
may be used in special circumstances. Focal zones should be
electronically adjustable. In general, the highest frequency capable
of adequate penetration to the depth of interest should be used. 1
When evaluating more supericial lesions, such as those within
the skin or those that are palpable and “pea-sized” or smaller,
an acoustic standof should be used (Fig. 21.11). his is either
an acoustic standof pad or a thick layer of acoustic gel that
allows better characterization of these areas. In some patients,
simply scanning with lighter compression can obviate the need
for a standof.
A
B
FIG. 21.11 Value of Standoff Pad. (A) Ultrasound evaluation of an epidermal inclusion cyst in the skin without a standoff pad did not
delineate the obstructed gland neck. (B) A thick layer of acoustic gel was then used and clearly shows the obstructed gland neck extending to the
skin surface (arrow).