Page 686 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

664 PART IV Specific Malignancies in the Small Animal Patient

Cats with cerebral meningiomas treated surgically often survive 11%. 104 Common causes of morbidity and early perioperative
in excess of 2 years, with reported MSTs ranging from 23 to 37 mortality include aspiration pneumonia, intracranial hemorrhage
3,29,87,88
Approximately 25% of feline meningiomas will
or infarction, pneumocephalus, medically refractory provoked sei-
months.
VetBooks.ir recur after surgery, with highly variable times to recurrence rang- zures, transient or permanent neurologic disability, electrolyte and
87,88
ing from 3 to 69 months.
78
osmotic disturbances, and thermoregulatory dysfunction.
Outcomes associated with surgical management of canine
meningiomas are more variable than those of feline meningiomas, Radiation Therapy
reflective of the previously identified operator and technical fac- RT is beneficial for the treatment of PBTs and SBTs when used
tors, in addition to the propensity for all grades of canine menin- as a sole or adjunctive therapeutic modality. As with other treat-
20
giomas to locally invade brain tissue. Most surgical studies of ments, extrapolating meaningful data from the veterinary brain
canine meningiomas have included superficially located cerebral or tumor RT literature with respect to the outcomes associated with
cerebellar convexity, falcine, parasagittal, or olfactory tumors. 90–94 specific tumor types in confounded by a general lack of histologi-
Surgical treatment of basilar, cerebellopontomedulary angle, fora- cally diagnosed tumors included in RT studies, grouping of het-
men magnum, parasellar, and tentorial meningiomas is techni- erogeneous intracranial masses in data analyses, and considerable
cally challenging and has not been frequently reported. When variability in the RT types and dose prescriptions used. RT equip-
90
standard cytoreductive surgical techniques are used, the MST ment and techniques have advanced to current predominantly
for canine meningiomas is approximately 7 months. 91–93 Stud- linear accelerator-based options, including intensity-modulated
ies describing the use of techniques or technologies that facilitate RT (IMRT) capabilities such as VMAT and tomotherapy, as well
removal of infiltrative tumor or intraoperative visualization such as stereotactic RT (SRT). The advantages of IMRT, VMAT,
81
as cortical resection, extirpation with an ultrasonic aspirator, or and SRT are improved target volume conformity, particularly
endoscopic assisted resection in canine meningiomas report supe- in volumes with complex shapes, and improved sparing of nor-
81
rior MSTs (16–70 months) compared with conventional surgi- mal tissues resulting in reduced risk for toxicities. SRT broadly
cal methods. 90,94 Dogs with meningiomas treated surgically also encompasses treatments that involve the precision delivery of high
benefit from the addition of adjunctive radiation therapy (RT), as doses of ionizing radiation to a stereotactically defined anatomic
MSTs associated with multimodal surgery and RT protocols range target in a limited number (1–5) of fractions, compared with the
from 16 to 30 months. 92,95,96 16 to 20 fractions for standard RT protocols. 9
There is a paucity of data regarding the potential efficacy of sur- Studies of cohorts of dogs treated with RT as a sole treat-
gery as a primary treatment of other PBTs, such as ependymomas, ment modality for brain tumors report MSTs ranging from
gliomas, and choroid plexus tumors, although a few individual 7 to 23 months when all treated intracranial masses are
animals with these tumor types experienced prolonged survival included. 81,96,106–111 MSTs associated with RT treatment of extra-
times (STs) after surgery or multimodal investigational thera- axial masses, the majority of which were presumptively diagnosed
pies. 7,21,84,97 Surgical removal of these tumors is seldom attempted meningiomas, range from 9 to 19 months; and MSTs reported for
because approaching and removing them is technically demand- intraaxial masses ranges from 9 to 13 months. 78, 81,96,106–111 Some
ing due to their intraaxial or intraventricular locations. In addi- RT studies report that extraaxial tumors have a more favorable
tion, as high-grade variants of these tumors are poorly delineated prognosis than intraaxial tumors. 110 Given the variable outcomes
and locally invasive, it is inherently more difficult to discriminate associated with both RT and surgery, there is currently no clearly
the margins of tumor from the neighboring neuropil. Clinician superior choice between these two modalities when either is used
attitudes and abilities with respect to the resection of these tumors a sole treatment for canine meningiomas. 78
types are evolving in parallel with improvements in brain imag- RT is also useful for the adjunctive therapy of canine menin-
ing techniques, intraoperative stereotactic and neuronavigational giomas, with combined surgical and RT therapy producing MSTs
systems, minimally invasive automated tissue resection devices, of 16 to 30 months. 92,95,96 Selected biomarkers have been shown
and “tumor painting” with fluorophores to assist with delineation to have prognostic value in dogs with meningiomas treated with
of tumors from the surrounding brain. 7,84,97,98 The literature also surgery and RT. In one study of 17 dogs treated with surgery and
suggests that the prognosis for some tumor types, such as HS, is adjunctive hypofractionated RT, survival was negatively correlated
poor, irrespective of the types of treatment administered. 99 with VEGF expression. The MST was 25 months for dogs with
8
Surgery also has utility in the management of some SBTs. tumors with 75% or fewer cells demonstrating immunoreactivity
Transsphenoidal hypophysectomy is an effective technique for to VEGF compared with 15 months for dogs with tumors with
the treatment canine and feline pituitary-dependent hyperad- greater than 75% of cell staining for VEGF, and dogs with tumors
renocorticism (PDH) and feline acromegaly, producing durable demonstrating more intense VEGF immunoreactivity also had a
endocrinologic and clinical remissions. 100–102 However, micro- significantly shorter MST. 112 Progesterone receptor expression has
surgical hypophysectomy has limited value in cases with pituitary also been shown to be inversely related to the tumor proliferative
macrotumors, is associated with a steep operator learning curve, index (PF PCNA index), which was predictive of survival in dogs
and is currently only offered at a few centers worldwide. 101,102 with meningiomas after surgery and postoperative RT. The 2-year
Some calvarial SBTs, such as multilobular osteochondrosarcoma progression-free survival rate was 42% for tumors with a PF PCNA
can also be managed surgically with good long-term outcomes index 24% or greater and 91% for tumors with a PF PCNA index
depending on histologic grade and completeness of excision (see less than 24%. 95
Figs. 31.4I, J). 103 Compared with palliative therapy, RT is effective at reduc-
The frequency of significant adverse events associated surgi- ing tumor size, improving neurologic signs, and providing a sur-
cal treatment of PBTs varies widely between individual studies, vival benefit in dogs and cats with pituitary tumors. 80,108,113–117
ranging from 6% to 100%. 29,78,84,87,88,90–92,98,104,105 If the outlier RT is the preferred therapeutic modality for pituitary macrotu-
study with 100% perioperative mortality is excluded from anal- mors. 80,115 In cases of PDH treated with RT, the reported rates of
ysis, the average rate of surgical adverse events is approximately endocrinologic remission are variable, with some studies reporting