Page 706 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

684 PART IV Specific Malignancies in the Small Animal Patient

nerve meningioma to maintain vision for several weeks to months.
RT may be helpful in the case of nasal tumors with orbital exten-
sion, in subtotally excised or recurrent meningiomas, and in other
VetBooks.ir select cases.

Prognosis
With conservative treatment, the prognosis for most tumors
involving the orbit and optic nerve is poor, 86,87 especially if
there is bony involvement on skull radiographs. Recurrence at
the primary site and involvement of adjacent or distant sites are
common, often occurring within weeks to a few months. Even
benign-appearing tumors such as lobular orbital adenomas and
orbital meningiomas may be locally invasive and have a propensity
for recurrence after wide excison. 84–90,96 In one study, however,
radical orbitectomy (with or without chemotherapy or RT) pro-
vided a local disease-free interval of more than 1 year in more than
50% of patients and a 70% survival rate for the first year. In
96
another study, the mean survival time for cats with orbital tumors
treated by RT, chemotherapy, or surgery that included resection
86
of affected orbital bones was only 4.3 months. In a study of 23
dogs with orbital tumors, most of which were treated by exentera-
tion with or without adjunct therapy, only three survived 3 years
• Fig. 32.8 CT (dorsal view) provides detailed information about the loca- or longer. The majority of these animals died as a direct result
87
tion and extent of orbital tumors, as in this 17-year-old cat with orbital of the tumor or were euthanatized at the time of diagnosis. 84–87
osteosarcoma.
86
may have a nondiagnostic FNA, especially in cases of SCC, Ocular Effects of Cancer Therapeutic
exploratory orbitotomy via a number of approaches 94–99 or exen- Modalities
teration may be required to characterize the mass and resect it if
possible. Cerebrospinal fluid taps may aid in distinguishing optic The ocular effect of external-beam RT for nasal and periocular
nerve neoplasia from optic neuritis. tumors can have a substantial effect on an animal’s quality of life.
Common complications include chronic keratoconjunctivitis,
Therapy corneal ulceration, “dry eye,” enophthalmia, entropion, cataracts,
Primary orbital and optic nerve tumors that lack metastasis or retinal hemorrhages, retinal detachments, and blindness. 100–103
regional lymph node involvement may be amenable to surgical Many of these conditions respond poorly to treatment, and vigor-
excision. If bony involvement is not present, orbital exenteration ous attempts at prevention should be made to avoid chronic ocu-
by widely dissecting around the mass (stripping periorbita if nec- lar pain and blindness. Recently intensity-modulated RT (IMRT),
essary) is usually the preferred procedure, as the advanced stage of which uses conformal avoidance, has been shown to significantly
the tumor at the time of diagnosis typically makes it impossible to decrease the ocular toxicity seen in dogs treated by RT for sponta-
excise the mass completely and preserve a functional or comfort- neous sinonasal tumors. 102,103
able eye. If periorbital bones are involved, radical “orbitectomy,” In humans, blurred vision, partial visual field defects, loss of
which resects the affected orbital tissues and surrounding bones, color vision, and diplopia have been associated with several anti-
96
should be considered. When treating optic nerve tumors, as neoplastic drugs. 104–107 Similar effects probably occur in ani-
much of the ipsilateral optic nerve as possible should be removed mals but would be difficult to detect. In addition, in humans,
in an attempt to obtain complete excision. 87 the bacillus Calmette-Guérin (BCG) has been associated with
If preservation of a comfortable eye and vision appears possible, uveitis; cyclophosphamide has been associated with dry eye; cis-
a variety of orbitotomy/partial orbitectomy techniques, ranging platin has been associated with neuroretinal toxicity; doxorubicin
from small incisions through the eyelid or mouth to reflection of has been associated with excessive lacrimation and conjunctivitis;
the zygomatic arch, temporalis muscle elevation, zygomatic pro- 5-FU has been associated with blurred vision, excessive lacrima-
cess osteotomy and ostectomy of a variety of orbital bony struc- tion, blepharitis, conjunctivitis, and keratitis; and vincristine has
tures have been described. 94–99 Recently orbital reconstruction been associated with cranial nerve palsies, optic neuropathy, and
techniques have also been described which improve the tectonic, cortical and night blindness. 104 Monoclonal antibodies directed
99
cosmetic and functional results of the procedure. Postoperative at the vasculature supporting the tumor also have been associated
complications are common and may include secondary enoph- with uveitis. 105 Antibody–drug conjugates have been associated
thalmia with entropion and possibly diplopia (double vision). with blurred vision, dry eye, and corneal abnormalities including
Surgical debulking as an alternative to “radical orbitectomy” can microcystic corneal disease. 106
be palliative, and some dogs may survive a year or more with mini-
mal therapy. Comparative Aspects
The role of chemotherapy and RT, either alone or as an adjunct
to surgery, is yet to be defined in the treatment of orbital tumors, Malignant melanoma of the choroid is the most common primary
although chemotherapy for orbital lymphoma may be effective. ocular malignancy in adult humans. Initially, it was believed that
Systemic corticosteroids may permit some patients with optic enucleation of these patients may enhance the risk of metastasis;