Page 32 - Zoo Animal Learning and Training

24 Section I: Diagnostics and Planning

Intracranial Imaging Tumor Resection/Biopsy
Based on advanced imaging a presumptive diagnosis is made and Intracranial neoplasms, even when aggressive, rarely metastasize.
consideration for surgery begins. Characteristics of the skull However, 23% of patients diagnosed with primary brain neoplasms
shape and brain lesion will influence patient positioning, surgical have primary neoplasms in other locations [15]. For this reason,
approach, and need for additional medical intervention. imaging of the thoracic cavity and abdomen are recommended
prior to surgery. Thoracic radiographs and abdominal ultrasound
are most commonly performed. Bicavitary CT may be done at some
institutions and is likely more sensitive, particularly in the detection
Specific Neurosurgery Considerations of pulmonary nodules (Figure 3.2) [16].
Any nodules, masses, or otherwise abnormal‐appearing organs
General Considerations should be aspirated at the clinician’s discretion to rule out signifi-
Most commonly, CBC, serum chemistry, and urinalysis have cant pathology. The presence of extracranial malignancies may pre-
been performed prior to surgery; in most cases this has been clude intracranial surgery for some patients or clients and certainly
done in association with presurgical neuroimaging. However, can worsen the overall long‐term prognosis. It may be difficult to
additional testing is recommended in some situations based on obtain a definitive diagnosis by fine‐needle aspirate. Splenic and
examination findings (see above) or surgical approach. In hepatic nodules are not uncommon in older dogs and adrenal
situations where surgical bleeding is anticipated, preoperative masses may be incidental in up to 57% of dogs (Figure 3.3) [17]. In
PCV and total solids (TS) is helpful for postoperative comparisons these situations, the risks and benefits of surgical or percutaneous
because it requires less blood than that needed for a CBC. If
there is a significant time lapse (1 week or more) between
previous blood work and the date of the surgical procedure,
abbreviated hematological and biochemical assessment should
be done including PCV/TS, blood glucose, and rapid azotemia
assessment. The most common protocols are summarized in
Table 3.1.
Increases in ICP and surgical bleeding can be lethal complica-
tions of intracranial surgery. All blood from the cranial vault even-
tually leaves via the jugular veins. Venipuncture of the jugular veins
and jugular catheters should be avoided when possible and blood is
preferably collected from a peripheral vessel. Neck collars, wraps,
and e‐collars should be avoided as well. When elevating the head,
an angle of 30° is appropriate and support should be ramp‐like with
padding extending from under the shoulder to the mid‐mandible to
avoid kinking of the cervical spine and vasculature. Elevated ICP
should be addressed medically as soon as detected. During surgery
maintenance of physiological mean arterial blood pressure is
critical. Autoregulatory mechanisms to maintain cerebral blood
flow at a rate of 50 mL per 100 g [1] are effective when systemic
blood pressure is kept between 50 and 150 mmHg. Outside of this
range or within injured areas, autoregulatory mechanisms fail. With Figure 3.2 Left lateral radiograph demonstrating diffuse pulmonary nod-
ules consistent with metastatic disease.
hypotension there is risk for decreased perfusion and ischemic
injury, and with hypertension ICP may rise and surgical bleeding
may worsen.

Table 3.1 The most common protocols for neurosurgical assessment.
Diagnostic test Tumor resection FMD VP shunt Trauma
Abdominal ultrasound √ +/–
Resting blood pressure √ +/– √
Blood type √ +/– +/–
CBC √ +/– +/– √
Chemistry √ +/– +/– √
Electrolytes +/– √ √ +/–
ECG √ +/–
PCV √ +/–
Thoracic radiographs √ +/–
Urinalysis √ +/–* +/–* √
*In otherwise healthy patients, PCV, TS, blood glucose, BUN, and urine specific Figure 3.3 Still image from an abdominal ultrasound of a patient with a
gravity may suffice. glioblastoma. Aspirates of the nodule were nondiagnostic and surgical
FMD, foramen magnum decompression; VP, ventriculoperitoneal. treatment was performed.