Page 1312 - Clinical Small Animal Internal Medicine

1250 Section 11 Oncologic Disease

Surgery to the current state utilizing 3D computer planning and
VetBooks.ir Intracranial modern technology. Long‐term efficacy of radiation
therapy alone is limited given the tolerance of the brain
Depending on the location, surgical intervention is rec-
ommended as a sole therapy for well‐circumscribed and as macroscopic tumor control is generally not as
rewarding as adjunctive treatment following cytoreduc-
meningiomas or a prelude to postoperative radiation tive surgery. Table 136.1 gives a summary of treatment‐
therapy and/or chemotherapy. Surgery alone for menin- related outcomes of CNS tumors.
gioma in dogs is associated with a median survival time Recently, stereotactic radiosurgical (SRS) approaches
of 4.5–7 months. Radiation therapy in the postoperative have been employed which allow for one or two fractions
setting has increased that median to 16–30 months. of high‐dose radiation to be delivered rather than the
Other surgical techniques such as ultrasonic aspiration conventional 15–25 daily fractions of lower doses per
or endoscopic‐assisted surgical resection have resulted fraction. This high dose per fraction is limited to the
in survival times of 41 and 70 months in dogs, demon- tumor and a small volume of normal surrounding tissue.
strating the utility of more aggressive approaches. This form of treatment theoretically minimizes the risk
Surgery as sole therapy for nonmeningioma tumors is of complications to normal tissues while providing abla-
more variable, case dependent, and generally results in tive doses to the tumor. SRS is still in the investigational
median survival times of months rather than years. stage in veterinary oncology and direct comparison to
Meningioma in the cat is often less aggressive and
invasive compared to the dog. Hence, the prognosis with conventional fractionated radiation therapy has not been
performed. However, preliminary results in the literature
surgery as sole therapy is good to very good with median are encouraging and the shortened overall treatment
survival times of 23–28 months. times and minimal dose to noninvolved tissues are
Surgical approaches to the pituitary gland (transsphe-
noidal hypophysectomy) have been described but man- attractive to both clinicians and owners and SRS likely
represents the future of radiation therapy for brain
agement is usually accomplished with fractionated neoplasia.
external beam radiation therapy or more recently radio-
surgical techniques in both dogs and cats.
Side‐Effects
Acute and late developing radiotherapy side‐effects vary
Spinal Cord depending on total dose given, dose per fraction, and the
Outcomes in dogs and cats with spinal cord neoplasia total volume and specific tissue type being irradiated.
are understandably highly variable and there is consider- Late‐term side‐effects are rare (<20%) but when they
able perioperative mortality due to poor return to func- occur, management is challenging as they are often life‐
tion. Overall median survival in one study of 37 dogs was threatening. Of the late effects, brain necrosis is the most
240 days if they survived 20 days following surgery, but common but others including spinal cord myelopathy
40% did not survive to that point. In a separate study can occur. Unfortunately, the clinical distinction between
evaluating surgery for intraspinal meningioma, clinical these late side‐effects and tumor recurrence is difficult
improvement was noted in all dogs surviving the periop- and often requires histopathology.
erative period but recurrence of clinical signs was at a Acute side‐effects of CNS irradiation are rare and
mean of 19 months. Only a minority were disease free often limited to surrounding normal structures in the
long term, thus indicating the need for postoperative treatment field such as the oral cavity, otic and ocular
radiation therapy. Postoperative radiation therapy did structures, and gastrointestinal tract. A syndrome of
appear to have a benefit based on time to neurologic delayed acute CNS effects can be seen several months
deterioration but recurrence of signs and/or tumor was after completion of radiation therapy and are manifested
still noted anywhere from 18 to 36 months. In cats by responsiveness to corticosteroids. This syndrome is
undergoing surgical treatment of spinal cord tumors, thought to be a transient demyelination of the white mat-
improvement was reported in 25/26 cases but the median ter rather than true necrosis which is the more classic
survival time for those with malignant neoplasms was delayed effect.
110.5 days, compared with 518 days for those with
benign tumors. In this study, the vast majority of cats Intracranial
eventually succumbed to disease‐related problems. Due to the limitations of available veterinary clinical
studies, the prognosis following irradiation of many pri-
mary intracranial tumors, especially those of glial origin,
Radiation Therapy
is largely unknown (see Table 136.1). Based on what has
Radiation therapy has evolved over the past several dec- been reported, median survival time following irradia-
ades from relatively unsophisticated planning techniques tion may range from four months to greater than four