Various versions of the
Silverman needle have long been employed in
percutaneous biopsies. The simple but elegant
structure of that instrument is well known and
self-evident on inspection.
In the photograph above, the
main body of the needle is shown with the
trochar inserted. The operator is holding the
tip of the central cutting needle and slightly
spreading the two arms of the needle tip to
demonstrate its bifurcated structure.
***
After the patient is comfortably
positioned and the position of the kidney has
been preliminarily determined by the
ultrasonographer, the operating physician may
wish to manipulate the transducer and determine
a "proprioceptive" sense of the approximate
position of the kidney in relation to obvious
landmarks.
***
Meticulous localization of the
kidney will be rewarded by a safe and productive
procedure.
A particularly successful
operating physician determines and marks a
"cross-hair" over the kidney area, as
illustrated in the following photograph.
After the transducer is located
over the lower pole of the kidney, a
straightened paper clip is centered beneath the
transducer and the projected ends of the paper
clip are used to define four points and the two
axes which intersect over the selected biopsy
site.
Note that one such point has
already been selected and marked with a pen, on
the patients skin, just beneath the thumb of the
physician.
The following figure illustrates
a biopsy site in which the "cross-hair" has been
marked, and the operating physician is holding
the transducer and performing a final recheck of
the image of the kidney in relationship to the
marked field.
***
The central spot in the
"cross-hair" defines the carefully point which
should be directly above the area on the lower
pole of the kidney where the biopsy needle will
be directed.
Now the sterile field may be
prepared and draped, and local anesthetic
injected.
After anesthetic is injected at
a depth near to the estimated depth of the
capsule of the kidney, ordinarily using a spinal
needle, the syringe may be detached and the
needle may be used as a "sound" delicately
probing the area in order to "feel" the capsule
of the kidney, its firmness contrasting with the
soft perirenal fat..
After the capsular surface of
the kidney is "palpated" by this "sounding"
procedure, the operating physician may 1) grasp
the needle shaft at the skin surface, 2)
withdraw the needle, and 3) measure the length
of the needle which extended from the skin
surface to the tip of the needle. This
measured length of the needle should be compared
to the estimated depth of the kidney previously
estimated by the ultrasonographer. The two
estimates should be comparable. If there is a
substantial disparity between the two
measurements, the depth of the kidney should be
re-estimated and the disparity resolved.
***
With the carefully estimated
depth of the kidney determined, a template may
be easily prepared as a guide to the operating
physician in determining the proper depth for
insertion of the Silverman needle.
In the photograph below note the
Silverman needle, a ruler, and a length of white
plastic material which is a segment of the
handle of a cotton swab, broken to length.
Having determined the probable
depth of the kidney (distance from the skin
surface to the capsule of the kidney, a segment
of white marker stick is broken to length, such
that 1) the length of the white stick segment
equals the distance from the hub of the needle
to the skin surface, and 2) the remaining length
of the Silverman needle is approximately equal
to the depth of the kidney.
The depth to which the needle
will need to be inserted, at the end of the
white segment and at the end of the ruler
(above) may be marked with a drop of antiseptic
solution or other visible mark. (See next
picture).
The brown mark on the shaft of
the Silverman needle is faintly visible. The
white template stick is at hand. A small skin
incision is made to allow introduction of the
Silverman needle.
***
The Silverman needle may now be
inserted in a vertical direction, stepwise, to
the estimated depth. After each stepwise
insertion, the operating physician will
carefully observe the needle for deflection
which may occur with regular synchronicity with
respiratory movements as the kidney is
approached and contacted by the needle.
As the surface of the kidney is
approached, the operating physician may withdraw
the trochar and insert the center cutting needle
(as in the picture above). By carefully " "percussing"
the tissues at the tip of the central cutting
needle, by lightly tapping the cutting needle
and feeling the resistance offered by the
underlying tissues, the skilled operating
physician may with impressive reliability be
able to judge when the cutting needle is
positioned exactly at the capsular surface of
the kidney.
The experienced operator, can,
after successfully executing the steps above,
reliably obtain a substantial and satisfactory
kidney biopsy in a very high percentage of
cases.
The final motions of executing
the biopsy do not lend themselves well to static
photographs. The steps involved may be
summarized as follows:
1) On instruction, the patient
suspends respiratory activity, ordinarily at
inspiration.
2) The central cutting needle is
crisply and with moderate force fully inserted
into the kidney, followed quickly by advancing
the outer cylinder of the needle, using a
rotational motion, to the desired depth,
followed by quickly removing the entire needle
assembly.
After the biopsy needle is
removed from the patient, the central portion of
the needle is extracted, the two sides of the
needle are spread apart, and the biopsy tissue
is carefully removed from the needle.
I have found it quite useful to
have the operating physician gently transfer the
biopsy to a small piece of paper which may then
be handed to the pathologist or his assistant
for examination. The operating field should
remain sterile, in case a second biopsy is
indicated.
A gauze sponge or similar
material should never be used to transfer the
biopsy tissue, since such cloth-like material
will adhere to the tissue excessively and cause
disruption of the biopsy.
Hard surfaced, non-absorbent
paper is an excellent transfer medium. Biopsy
kits often contain small brochures, labels, etc.
which are convenient sources for such paper.
Evaluation and allocation of the biopsy
tissue by the pathologist is described above.
