Page 701 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 32 Ocular Tumors 679

it may be difficult to arrive at a definitive diagnosis without invad-
ing the eye or removing it because organizing blood clots are not
always distinguishable from neoplastic mass lesions. Because most
VetBooks.ir anterior uveal brown or black masses are cystic and not neoplastic,
transillumination should be attempted before more invasive pro-
cedures. Uveal cysts typically permit bright light to pass through
them, are roughly spherical, and may be attached to the ciliary
body or free-floating in the anterior chamber. Once suspected,
most primary canine intraocular tumors are observed for progres-
sion, although occasionally FNA (with its risks of inflammation,
infection, and hemorrhage) or attempts at intraocular resection
or enucleation are used for diagnostic purposes. The possibility of
metastasis from another primary site (i.e., oral cavity or nail bed)
to the eye or from the eye to other organs should be eliminated.
Therapy
Canine primary intraocular tumors are often carefully observed,
although surgical intervention (sector iridectomy/cyclectomy,
• Fig. 32.5 Most anterior uveal melanomas originate from the iris or ciliary laser ablation, enucleation) should also be considered. Digital
body and are benign. photographs are a valuable aid in assessing progression. Enu-
cleation is advised if there is concern about malignancy or if
complications such as intractable uveitis, chronic hyphema or
mitotic rate being the most important. 30,31 Benign tumors have secondary glaucoma occur. In the COPLOW collection, 14%
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fewer than two to four mitotic figures/10 HPFs (mitotic index), of canine globes with glaucoma that are removed also had mela-
and malignant tumors demonstrate nuclear pleomorphism and a noma. The low risk of metastasis and unproved efficacy of enu-
mitotic index of at least four and often more than 30. Destruction cleation at preventing metastasis in the few malignant tumors
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of the eye is not by itself sufficient for a diagnosis of malignancy. that have been reported make it difficult to automatically advise
The overall rate of metastasis of intraocular melanomas is approxi- enucleation of normotensive, noninflamed, visual eyes. Iso-
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mately 4% and usually occurs via the hematogenous route. lated primary masses involving only the iris or a portion of the
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Local spread along ocular vessels and nerves or via direct penetra- ciliary body may be amenable to local resection by sector iri-
tion of the sclera or cornea also occurs. Benign tumors tend to be dectomy/cyclectomy to preserve the eye and vision. 32,40 These
smaller, more darkly pigmented and have a lower mitotic index intraocular procedures, however, require an accomplished oph-
than malignant tumors. 30,31 thalmic surgeon and often have unsatisfactory long-term results.
Circumscribed, nevus-like pigmented iridal growths have been Transscleral and transcorneal Nd:YAG or diode laser therapy
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described in young dogs (7 months to 2 years old). The natural has induced remission in some small- to moderate-sized primary
history of these lesions is variable because enlargement may not intraocular tumors. 43,44 Specialized goniolenses may also allow
occur over several years. 32,40 Some, however, are capable of rapid laser treatment of masses that have invaded into the iridocorneal
growth, but to date all are clinically and histologically benign. angle. Although the results were variable, perhaps because these
Ocular melanosis of Cairn terriers resembles feline diffuse iris tumors varied histologically in nature, laser therapy holds prom-
melanoma in some respects. This disorder is probably an auto- ise for the palliation or potential cure of a number of intraocu-
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somal-dominant condition with a variable age of onset and rate of lar tumor types while also preserving vision. Metastasis was not
progression. It results in a thickening and pigmentation of the iris, observed after this procedure, although this obviously remains a
release of pigment into the aqueous, pigment deposition in the risk when the tumor is malignant.
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sclera/episclera, and to a lesser extent posterior segment pigment
deposition. Secondary glaucoma is common, and overt uveal Prognosis
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melanocytic neoplasia occurs in a small percentage of dogs. Although the data in most studies are heavily “censored,” the prog-
nosis for histologically benign melanomas appears to be excellent.
History and Clinical Signs Enucleation is curative, but attempts at local excision or laser pho-
Common presentations of intraocular tumors include a visible toablation may be only palliative, especially if the ciliary body or
intraocular or scleral mass, glaucoma, hyphema, anterior uveitis, trabecular meshwork is involved. The presence of black, nonsolid
or extrabulbar spread, or they can be an incidental finding during material within the orbit after the enucleation of benign mela-
an ophthalmic examination. 30,41 Because glaucoma or hyphema nomas with scleral invasion apparently does not affect prognosis
are often the only overtly visible clinical signs, 30,41 intraocular because these cells appear incapable of continued growth. In one
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neoplasia should always be considered in animals with hyphema, study, approximately 25% of histologically malignant melanomas
glaucoma, or both when there is no history of trauma or coagu- demonstrated metastasis, typically within 3 months of enucle-
lopathy. Small masses frequently create few symptoms other than ation, and most dogs with metastasis were euthanatized within 6
pupillary distortion. Pigmentation is variable and not a reliable months of enucleation. This surprisingly poor prognosis has not
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indicator of tumor type. been the experience of cases followed recently in the COPLOW
data set, and in a larger study, dogs with tumors classified as malig-
Diagnostic Techniques and Workup nant were reported to have only a somewhat decreased survival
Usually, the clinical or ultrasonographic appearance (if the media time compared with dogs with melanocytoma and dogs from a
are opaque) is strongly suggestive of intraocular neoplasia, although control population.
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