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48 Section I: Diagnostics and Planning

than the meningiomas. Vascular supply to the intracranial tumors canine skull. A description of a typical CT‐guided brain biopsy
was detected by color Doppler and aided in directing the approach procedure in dogs using the modified Pelorus Mark III Stereotactic
to the masses using the ultrasonic aspirator [154]. System has been published [159,160]. Accuracy of biopsy needle
Correlating the preoperative MRI or CT images with the intraop- placement was determined by comparing the x, y, and z coordinates
erative ultrasound images was very valuable to the surgeons in gain- of the biopsy target site with the actual coordinates of the needle tip
ing a perspective of the size of the mass, the proximity of ventricles, on CT images. Mean needle placement error was 3.5 ± 1.6 mm.
the eloquent areas of the brain, and the location of larger blood ves- Needle placement error was not significantly related to operator
sels. In addition, the serial images consistently gave the surgeons a experience, dog size (body weight), or needle path length, although
definitive perspective on the completeness of the resection and needle placement error was significantly affected by lesion location
helped differentiate grossly abnormal from grossly normal struc- [160]. CT‐guided stereotactic brain biopsies were performed on 50
tures. Postoperative imaging correlated well with ultrasound imag- consecutive dogs using this system [159]. Based on available histo-
ing at the conclusion of the surgeries. The authors conclude that the pathological samples (stereotactic biopsy, n = 50; surgery, n = 17;
use of intraoperative ultrasound imaging is a valuable adjunct and necropsy, n = 9) the patient population consisted of 34 dogs with
correlates well with both preoperative and postoperative advanced primary brain tumors, two with invasive nasal adenocarcinomas,
imaging. Intraoperative ultrasound should be a standard imaging and 13 with nonneoplastic brain lesions. Brain tissue was not
modality for intracranial procedures. Additional development of obtained from one dog. In 22 dogs a final diagnosis was made from
this technique, including the use of three‐dimensional ultrasound, tissue subsequently obtained from surgical resection or at necropsy.
is warranted. Intraoperative ultrasonography is helpful in localizing The final diagnosis was in agreement with the stereotactic biopsy
and defining the margins of intracranial masses and accurately diagnosis in 20 of these 22 dogs. In 17 other dogs without follow‐up,
determines the extent of resection, as confirmed by postoperative stereotactic biopsy provided a diagnosis of a specific primary brain
MRI or CT [154]. tumor subtype.
Postoperative complications associated with the biopsy proce-
Image‐guided Brain Biopsy in Veterinary Patients dure were assessed in 41 dogs. The other nine dogs either went
Needle biopsy may be performed either “‘freehand,” usually to directly to surgery (n = 7) or were euthanized (n = 2) immediately
access very superficial lesions through a burr‐hole created follow- after the biopsy procedure; 36 dogs recovered without apparent
ing imaging and localization (with or without the assistance of clinical complications. Postoperative clinical complications in the
ultrasonography), or using a stereotactic frame to guide the needle, remaining five dogs included transient epistaxis (one dog), tran-
again following imaging and localization. Freehand fine‐needle sient exacerbation of cerebellar signs (one dog), obtundation pro-
aspiration may also be performed on superficial lesions. gressing to coma (one dog), and medically uncontrollable seizures
Stereotactic biopsy is generally performed using a side‐cutting (two dogs). The latter three dogs with severe neurological compli-
brain cannula. The cannula is a blunt‐ended needle with an inner cations all had large primary brain tumors and had been receiving
and outer sheath, both of which contain a lateral window. Once high doses of phenobarbital and glucocorticoids to control seizures
the cannula is introduced into the region to be sampled, tissue is at the time of biopsy. These results suggest that this CT‐guided
drawn into the inner sheath using gentle suction applied via a biopsy procedure can provide an accurate pathological diagnosis of
syringe attached to the end of the cannula. The inner sheath is brain lesions detected by CT and MRI neuroimaging [159].
then rotated through 180° in relation to the outer sheath; the A more recent study evaluated a Kopf stereotactic system, a com-
sharp edges of the lateral window of the inner sheath excise the mercially available patient restraint system that does not require
brain fragment within the inner sheath using a guillotine action. additional modification for use in small animals [40]. The accuracy
The sample is then collected by withdrawing the inner sheath of biopsy needle placement was determined by injecting dilute
from the outer sheath. Stereotactic needle biopsy has been used in iohexol into cadaver brains and comparing the three‐dimensional
human neurosurgical institutions extensively over the past two coordinates of the desired target location to the actual needle tract
decades, and stereotactic frames and biopsy systems have now observed on postcontrast CT images. Overall mean error in needle
been developed for use with dogs and cats, although they are not placement in a dorsoventral trajectory was 0.9 ± 0.9 mm (n = 80
yet widely available [10,40,155–161]. injections) for dogs and 1.0 ± 1.1 mm (n = 30 injections) for cats.
Frameless stereotactic systems have also been developed which The overall mean error in needle placement via an oblique trajec-
utilize cameras and fiducial markers placed on the skin to triangu- tory in five dogs was 1.7 ± 1.6 mm (n = 12 injections). Another
late the position of the tip of the biopsy needle in three‐dimensional study assessing a different device evaluated its accuracy on 23 cli-
space and reference this to previously acquired CT or MRI images ent‐owned dogs which presented with a brain lesion [157]. Biopsy
in real time. of the lesion was achieved in 95% of cases. The target tissue was not
sampled in one dog. Complications were observed in six dogs. Two
CT‐assisted Biopsy dogs with highly vascularized brainstem tumors died after CT‐
The most well‐documented CT‐guided brain biopsy system in vet- guided stereotactic brain biopsy. Minor complications (slight varia-
erinary use is a modification of the Pelorus Mark III Stereotactic tion in the neurological status) were observed in a further four
System, which is a commercially available device for CT‐guided cases. A diagnosis was reached in 16 dogs after cytological exami-
stereotactic brain biopsy in humans [159,160]. This device has been nation and in 21 dogs after histological evaluation.
used to safely and accurately perform CT‐guided stereotactic brain
biopsies in dogs with intracranial lesions. Modifications were nec- MRI‐assisted Biopsy
essary to accommodate a 90° shift in orientation of the canine head The Brainsight™ system is an example of a frameless stereotactic
compared with the human head during the imaging phase of MRI device developed for use in animals, and has the advantage of
the procedure, and to facilitate other phases of the biopsy procedure allowing both needle biopsy and intraoperative navigation to be
that are affected by the uneven and variable topography of the performed during open craniectomy (Figure 4.25) [161]. A recent