Diagnostic ultrasound ( PDFDrive )

CHAPTER 17 Ultrasound-Guided Biopsy of Chest, Abdomen, and Pelvis 603
A bobbing or in-and-out jiggling movement of the biopsy
needle during insertion improves needle visualization. his
bobbing motion causes delection of the sot tissues adjacent to
the needle and makes the trajectory of the needle much more
discernible within the otherwise stationary ield. Alternatively,
if using a coaxial system, the inner, smaller needle can be
“pumped” or moved in and out within the larger cannula.
Needle visualization can also be improved by increasing the
relectivity of the biopsy needle. Large-caliber needles are more
readily visualized than small-caliber needles. Keeping the bevel
of the needle directed toward the transducer may also increase
the conspicuity of the needle tip. Some authors have found CDFI
helpful to visualize needle motion, 43 although we have not
routinely incorporated Doppler ultrasound into our practice.
Modiications in needle tip design to enhance needle visualization
include scoring the needle tip and using a screw stylet. Extrarelective
needles speciically designed for ultrasound guidance are
commercially available. Most needles, however, are suiciently
visible sonographically as long as the needle and transducer are
aligned.
he echogenicity of the parenchyma of the organ undergoing
biopsy also afects the visibility of the biopsy needle. If the
parenchyma is relatively hypoechoic, such as liver, kidney, or
spleen, the echogenic needle can usually be identiied easily.
Conversely, if the organ or sot tissues are relatively hyperechoic,
it is usually diicult to visualize the echogenic needle tip in this
background. his is particularly relevant in the biopsy of masses
in obese patients or masses surrounded by complex fat, as in
the retroperitoneum.
Linear or curved array transducers are frequently used for
guiding procedures because of their good near-ield resolution,
which allows visualization of the needle ater relatively little tissue
penetration. he focal zone of the ultrasound beam should
also be placed in the near ield for better needle visualization.
Sector transducers are oten used if there is a small acoustic
window or if there is a deep lesion where a steep needle approach
will be needed.
Clear visualization of the biopsy needle is an important element
in the success of ultrasound-guided needle biopsies. he various
techniques described here can be used to enhance needle visualization.
However, considerable real-time scanning experience
remains the key factor to the successful performance of
ultrasound-guided biopsies.
Speciic Anatomic Applications
Liver
he liver is the abdominal organ in which percutaneous biopsy
is most frequently performed. Common indications for biopsy
include nonsurgical conirmation of metastatic disease, characterization
of focal liver mass(es) with inconclusive imaging, and
diagnosis of parenchymal disease, although random parenchymal
biopsies have decreased at our own institution as a result of
increasing utilization of elastography for liver ibrosis evaluation.
Biopsy of large or supericial lesions is most easily done. With
experience, deep lesions and lesions smaller than 1 cm can
undergo accurate biopsy 44,45 (Fig. 17.4).
A
B
FIG. 17.4 Ultrasound-Guided Biopsy of Small Hepatic Metastasis.
(A) Longitudinal ultrasound image of inferior right lobe of the liver
shows a 1-cm mass (arrow). (B) Gross photograph of the core biopsy
sample shows the typical white core of pathologic tissue (arrows) bordered
by typical-appearing normal liver parenchyma (arrowheads).
In our practice, liver biopsy is almost universally performed
under ultrasound guidance because of the real-time visualization
of the needle. his advantage becomes particularly obvious when
there is signiicant movement of the liver caused by respiration
and diaphragm excursion.
Lesions in the let lobe of the liver and in the inferior portion
of the right lobe can usually undergo biopsy through a subcostal
approach. Lesions located superiorly in the dome of the liver
present a technical challenge for traditional CT-guided biopsy,
but real-time, of-axial imaging with ultrasound allows for accurate
needle targeting of such tumors, oten through an intercostal
approach. Although the intercostal approach may violate the
pleural space, aerated lung is rarely punctured because it is well
visualized sonographically and can be avoided. We usually place
the patient in a let posterior oblique rather than supine position
when an intercostal approach is used to improve visibility of the
liver. If working along the right side of the patient, such a position
also prevents the patient from watching needle manipulation.
As feasible, orienting the transducer along the longitudinal
axis of the patient is preferable. Such orientation minimizes the
interference of respiration, because the tumor and needle remain
in the ield of view throughout the procedure.
Benign hepatic lesions such as focal fatty iniltration, focal
areas of normal liver within a fatty iniltrated liver, cavernous
hemangiomas, focal nodular hyperplasia, and even atypical
hemangiomas can usually be conidently characterized as benign
by magnetic resonance imaging (MRI) of the liver. However,
they occasionally mimic the appearance of malignancy on imaging
studies. Biopsy of these processes can be done with ultrasound
guidance to exclude malignancy and to conirm their benign
nature if MRI indings are equivocal and especially if the