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INTERVENTIONAL AND OTHER TECHNIQUES 257
Figure 11.4 Spring-loaded gun designed to operate the
cutting needle.
As an alternative to the gun/needle combination
a number of ‘self-fire’ needles are available.
This is essentially a single-use spring-loaded biopsy
needle. Again these come in a variety of sizes but
their advantage is that they are easier and lighter to
use than the gun/needle combination, and therefore
are easier employed in the CT situation. Most
departments will tend to utilize a combination of
both.
In cases where the clinician is not familiar with
ultrasound techniques, appropriate guidance by
a sonographer, while the clinician biopsies, is
highly successful, quick and avoids potential
complications.
Fine-needle histology, involving the use of needles
of 21 gauge or less, reduces even further the
possibility of postprocedure complications. These
are generally not used as only small amounts of tissue
are obtained for analysis and, as thin needles,
they are apt to bend more easily, and are therefore
more difficult to see and retain within the plane of
the scan. Biopsy of deep lesions is therefore more
difficult, if not impossible.
Fine-needle aspiration cytology
Cytology is the analysis of cells rather than the core
of tissue obtained for histology. This is generally
more difficult to interpret pathologically, as the
characteristic architecture and intercellular relationships
seen in a histological sample are absent.
It has the advantage, however, of allowing a finer
needle to be used. This can be passed through
structures, for example the stomach, blood vessels,
en route to the site of interest, with no adverse
effects.
Fine needles for cytology are of 21 gauge or
smaller. They are of a simple design with a bevelled,
hollow core and no cutting mechanism.
The needle is introduced under ultrasound
guidance to the required position. Fragments of
tissue are removed into the needle by applying
negative (sucking) pressure with a syringe to the
needle, while moving the needle to and fro to
loosen the tissue.
These can then be expelled on to a microscope
slide and smeared. The main disadvantage of this
technique is that it requires a highly trained and
specialized pathologist to interpret the samples,
whereas all trained pathologists can view histological
specimens. In addition, for many conditions,
histological diagnosis is required, although
cytology remains a useful tool in the breast and
thyroid.
ULTRASOUND-GUIDED BIOPSY
PROCEDURES
Liver biopsy
The most common reason for ultrasound-guided
biopsy is for suspected metastatic disease. The liver
is one of the most common sites for metastases and
histology is often required to confirm the diagnosis,
or to identify the origin of an unknown primary
lesion (Figs 11.5 and 11.6).
Biopsy of other focal lesions in patients with
chronic liver disease (for example, cirrhosis, hepatitis
B or C) in whom there may be suspected hepatocellular
carcinoma and occasionally in patients
with benign disease (for example, capillary haemangiomas
or focal nodular hyperplasia) can also
be performed, although MRI and contrast ultrasound
are increasingly used to characterize lesions,
without recourse to biopsy.
Focal lesion biopsy is generally safely and accurately
performed with an 18G Tru-Cut needle
which yields reliable tissue for histological analysis.
In general an accuracy of 96% should be achievable
2 (Fig. 11.7).
In addition to focal lesion biopsy another
common reason for liver biopsy is to assess the