Figure 4. A contrast-enhanced transverse CT image of an 11-year-old dachshund with acute signs of right forebrain disease.
A contrast-enhancing lesion is evident in the white matter in the right temporoparietal lobe (arrow). Ventricular asymmetry
is also evident (arrowheads).
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After a sterile scrub is done on the target area, a small skin incision is made. The underlying muscles are also incised and
dissected from the calvaria, and a hand drill is used to make a small hole in the calvaria. The apparatus holding the biopsy
needle is then mounted over the patient's head, and the needle is aligned to the lesion by using serial transverse CT scans.
A Sedan Side-Cutting Biopsy Needle (Elekta) is used, which is a 2.1-mm-diameter side-holed brain cannula that includes an
outer and inner needle (Figure 2). The outer needle has a blunt, nonbeveled end, while the windows have cutting edges. The distance from the tip of the needle
to the center of the lesion is measured by using CT, and the surgeon then advances the needle (Figures 3-5). Two or three samples are usually collected through the lateral window of the biopsy needle. A gentle negative pressure
is created with a 10-ml syringe applied to the proximal end of the inner needle to introduce the sample to be collected into
the needle window, and the inner biopsy needle is rotated 180 degrees to cut the collected sample. The inner needle is then
removed (the external needle is left in place), and the sample is extracted by flushing the needle with air.
After collecting the first proximal sample, the inner needle is replaced into the external needle, and both needles are advanced
to a precise location, according to the CT measurements, to obtain one or two additional samples. (We collect at least one
sample from the center of the lesion and one from the periphery.) The samples are submitted for cytologic and histologic examination
and bacterial and fungal culture and antimicrobial sensitivity testing. To ensure that the samples are diagnostic, the cytologic
examination is performed before the apparatus is removed.
Figure 5. The same dog as in Figure 4. Under the guidance of contrast-enhanced transverse CT scans, the biopsy needle is advanced into the exact location of the
lesion. In this case, the histologic diagnosis was granulomatous meningoencephalitis. At the time of the definitive diagnosis,
the dog was already receiving corticosteroids, and its neurologic signs were severe. Combination prednisone and cyclosporine
therapy was initiated and partially reversed the neurologic signs, and during the following three weeks the dog improved from
nonambulatory tetraparetic to ambulatory hemiparetic. At an 8-month recheck, the dog exhibited only ataxia, and the owner
is happy with the outcome
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Typically, this procedure takes about two hours. Potential risks are the same as those reported with the stereotactic technique
and include seizures, intracranial bleeding, coma, and death. Usually patients are kept in intensive care for 24 hours, allowing
clinicians to administer supportive care, monitor vital signs, and detect any signs of neurologic deterioration. Patients
are usually discharged 48 hours after the biopsy.
Why use this technique?
A definitive diagnosis allows clinicians to give owners a more exact prognosis, which can also help clinicians determine whether
treatment is likely to succeed.The procedure is being done at the University of Wisconsin, School of Veterinary Medicine.
It has been used in dogs to diagnose granulomatous meningoencephalomyelitis and various brain tumors; however, it could also
be applied in cats. The procedure costs $1,200, and preoperative testing is required, including an MRI scan that costs $1,800,
to determine whether a lesion is present. If you would like more information about this procedure, write to Dr. Filippo Adamo
at the Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin, 2015 Linden Drive West, Madison,
WI 53706; call (608) 263-7600; fax (608) 265-8276; or e-mailadamopf@svm.vetmed.wisc.edu
.
REFERENCES
1. Koblik, P.D. et al.: CT-guided brain biopsy using a modified Pelorus Mark III stereotactic system: Experience with 50 dogs.
Vet. Radiol. Ultrasound 40 (5):434-440; 1999.
2. Moissonnier, P. et al.: Stereotactic CT-guided brain biopsy in the dog. J. Small Anim. Pract. 43 (3):115-123; 2002.
3. Moissonnier, P. et al.: Accuracy testing of a new stereotactic CT-guided brain biopsy device in the dog. Res. Vet. Sci. 68
(3):243-247; 2000.
The information for "On the Forefront" was provided by Filippo Adamo, DVM, DECVN, Department of Medical Sciences, School of
Veterinary Medicine, University of Wisconsin, Madison, WI 53706.
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