Diagnostic ultrasound ( PDFDrive )

600 PART II Abdominal and Pelvic Sonography
are traditionally used to obtain cells for cytologic analysis by
using a procedure commonly referred to as ine-needle aspiration
(FNA). However, small pieces of tissue may be obtained for
histologic examination as well. With these small-caliber needles,
masses behind loops of bowel can be punctured with minimal
likelihood of infection. 4 he smaller samples yielded by smallcaliber
needles are appropriate to conirm tumor recurrence or
metastasis in a patient known to have a previous primary
malignancy. Even if the sample is small, the pathologist is usually
able to make an accurate diagnosis by comparing the biopsy
specimen with the original tissue.
Large-caliber needles can be used to obtain greater amounts
of tissue for more thorough histologic and cytologic analysis.
Larger needles may be necessary to obtain suicient tissue to
diagnose and subtype some types of malignancies (e.g., lymphoma),
many benign lesions, and most chronic difuse parenchymal
diseases (e.g., hepatic cirrhosis, renal glomerulonephritis,
renal allograt rejection). 36 he large-caliber tissue sample can
also be used to generate an additional “touch prep” specimen,
whereby the tissue is manually swiped across a glass pathology
slide, leaving a cellular sample on the slide for cytologic
analysis. 37
he preference and level of expertise of the pathologist involved
in the interpretation of biopsy specimens are considerations in
the selection of needle size and type. Cytopathologists specialize
in the interpretation of cellular samples, rendering a diagnosis
based on the cells provided. Unfortunately, some clinical facilities
do not ofer cytopathologic interpretation. Histopathologists,
in contrast, oten prefer a large biopsy specimen for interpretation.
For example, a large biopsy specimen from a metastatic lesion
oten allows a more reliable prediction of the primary site of the
malignancy than a tiny sample or a cytologic aspirate. Determination
of the primary site allows the oncologist to tailor subsequent
treatment.
Biopsy Procedure
Before any invasive procedure is performed, the procedure, risks,
alternatives, and beneits should be explained in terms that the
patient can understand so that informed consent can be obtained.
he performing physician must address patient apprehension
about potential pain during the procedure and possible complications
of the biopsy. Ater discussing the procedure, any patient
questions should be answered fully.
Biopsies are frequently performed on an outpatient basis.
Discomfort during the procedure is rarely severe and is usually
controlled by appropriate administration of local anesthetic ater
the skin is cleaned and draped. An IV access may be established
before the biopsy in the event that luid or medications are
necessary during the procedure. Premedication is usually not
necessary. Sedatives and analgesics such as midazolam or fentanyl
can be administered intravenously ater consent has been
obtained. 38 In patients with an increased risk of bleeding, a larger
or second IV access site may be prudent.
here are two options to sterilize the transducer. he transducer
may be covered with a sterile plastic sheath, although
this may degrade image quality and make the transducer more
diicult to handle. Alternatively, the transducer itself may be
directly sterilized and placed directly on the skin. Sterile gel
is used as an acoustic coupling agent. Ater the biopsy, the
transducer is soaked for 10 minutes in a bactericidal dialdehyde
solution.
Most ultrasound-guided biopsies are performed under continuous
real-time visualization. Needle guidance systems designed
to facilitate proper needle placement are commercially available.
hese guides attach to the transducer and direct the needle to
various depths from the transducer surface, depending on the
preselected angle of the guide relative to the transducer (Fig.
17.1A,B). Many radiologists prefer the “freehand” technique in
which the needle is inserted through the skin directly into the
view of the transducer without the use of a guide (Fig. 17.1C).
he needle is then independently directed to the target lesion by
the operator under real-time ultrasound visualization (Videos
17.3 and 17.4).
In contrasting these two biopsy techniques, one can appreciate
the technical ease provided by the needle guidance method. his
can decrease the time to perform a biopsy, particularly in the
hands of a novice operator. 39 However, the freehand technique
allows greater lexibility to the operator in performing subtle
adjustments to the needle path in the event of patient movement,
particularly with respiration.
FNA biopsies are performed by placing the tip of the needle
into the target lesion and rapidly “bobbing” the needle within
the mass, collecting cellular samples within the lumen of the
small needle. Some biopsy devices include a syringe on the end
to provide negative pressure within the lumen, increasing the
cellular yield.
Large-caliber needles are used to obtain cores of tissue. With
the typical spring-loaded core biopsy device (biopsy “gun”), the
needle tip is advanced to the margin of the target lesion. Careful
attention is made to the anticipated excursion of the device to
prevent injury to deeper structures. Some biopsy devices allow
initial manual advancement of the stylet through the target lesion
to the desired depth. When the spring-loaded cutting sheath is
activated, the sheath advances over the stylet, but there is no
additional forward motion of the needle (Fig. 17.2).
Most biopsies are performed by making one or more passes
into a mass with a single needle. Occasionally, two needles are
used in a coaxial manner, whereby a larger introducer needle
is irst placed into the mass. he inner stylet of this needle is
then removed, and a longer, smaller-caliber needle is placed
through its lumen. Multiple samples can then be obtained with
the smaller needle without the need to reposition the larger
introducer needle. his technique allows a large amount of tissue
to be obtained with only one puncture of the organ capsule,
although gas introduced during the procedure may interfere
with ultrasound imaging. Although intuitively this should decrease
bleeding complications, this has not been conclusively demonstrated
in real practice. 40 his may be related to the large caliber
of the introducer needle or the extended time during which the
introducer needle lies within the organ, potentially tearing the
capsule.
Ater the biopsy is performed, the patient is typically observed
in the radiology department for a period commensurate with
procedure risk. Longer observation may be appropriate if there