Page 704 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

682 PART IV Specific Malignancies in the Small Animal Patient

and prognosis may be accurately determined. There is reason to with potentially fatal metastasis has been described in dogs. 76,77
believe that the prognosis is considerably better if enucleation is These tumors are rare (0.2% of COPLOW’s canine tumors) and
affected dogs usually have long-standing disease thought to be
performed before the tumor invades the optic nerve or extends
VetBooks.ir beyond the sclera. To date, there have been no reports of treat- inflammatory or traumatic. One retrospective study reported that
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13% of cases had a history of known or suspected ocular trauma
ment by RT or chemotherapy.
Extraocular extension is common, as is recurrence after orbital and 33% received an intravitreous gentamicin injection for the
exenteration. 58,61 Continued growth up the remainder of the treatment of glaucoma. 77
optic nerve into the chiasm and brain, with vision loss or other Clinical signs include a retroiridal mass that may displace
neurologic signs, involvement of regional lymph nodes, and dis- the iris or lens by expansive growth, and if the tumor is large,
tant metastasis, has been reported. 47,59 The vast majority of ani- secondary glaucoma, ocular pain, and intraocular hemorrhage
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mals die of local invasion and recurrence, typically within several may be noted. The diagnostic workup and differential diag-
months of enucleation. 58,61 nosis are similar to that of anterior uveal melanomas. Given the
high frequency of ciliary body cysts in some predisposed breeds
(especially the golden retriever), it is essential to differentiate cili-
Spindle Cell Tumors (Uveal Schwannoma) of ary body tumors from a benign cystic lesion before enucleation.
Blue-Eyed Dogs Cystic lesions, which rarely require any intervention, are usually
seen as lightly pigmented, ovoid, retroiridal masses that can be
Dogs with a blue, or partially blue, iris appear to be at risk of shown to be hollow by transillumination or hypoechoic by ultra-
developing a spindle cell sarcoma in the uvea. 68,69 These tumors sonography. Early enucleation of ciliary body tumors has been
usually involve the iris but can originate or extend into the cili- recommended, although benign adenomas may remain static for
ary body, choroid, and even the vitreous. Breeds that commonly years, making enucleation controversial for small tumors unas-
have blue irides are more likely to develop an iridal spindle cell sociated with secondary ocular disease. Local intraocular resec-
sarcoma, but any dog with any blue in its iris appears to be at risk. tion or laser photoablation may permit vision and ocular comfort
The origin of these tumors is thought to be Schwann cells of non- to be maintained for at least some period of time. However,
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myelinated peripheral nerves and the term “uveal Schwannoma in one study, the vast majority of local excisional biopsies for
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of blue-eyed dogs” has been proposed. 69,70 The cells stain posi- iridociliary epithelial tumors had “dirty” margins and of the 19
tive with glial fibrillary acidic protein (GFAP), as do the Schwann dogs with follow-up only four did not have recurrence (which
cells of nonmyelinating nerves. In a case series involving 11 dogs, occurred an average of 23 months postbiopsy). In that study, ade-
more than half of the tumors were not clinically recognized and nomas were indistinguishable from adenocarcinomas on the basis
the diagnosis of neoplasia was not made until histopathology was of biopsy alone, although adenocarcinomas seldom metastasize.
performed. Metastatic disease appears uncommon, although one Complications of excisional biopsy include tumor recurrence,
case has been reported and local recurrence within the scleral shell intraocular hemorrhage, chronic uveitis, cataract, glaucoma, lens
was seen in another dog that had been treated by evisceration and displacement and retinal detachment. Systemic administration of
placement of an intrascleral prosthesis. 68,70 5-fluorouracil (5-FU) has been described as an adjunct to local
resection of ciliary body tumors, but the efficacy of this therapy
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Iridociliary Epithelial Tumors is unknown.
Primary iridociliary epithelial tumors (ciliary body adenomas,
adenocarcinomas, pleomorphic adenocarcinoma, and less com- Secondary Uveal Neoplasms
monly, medulloepitheliomas and other primitive neuroectoder- Numerous malignant tumors, especially adenocarcinomas, have
mal tumors [PNETs]) are the second most common primary been reported to metastasize to the highly vascular uveal tract.
intraocular tumors in dogs after melanocytic neoplasms and the Metastatic tumors to the eye in dogs account for approximately
third most common in cats. 71,72 They account for 12% of all 5% of all tumor submissions in the COPLOW database. Of those,
canine and 3.5% of all feline tumors in the COPLOW database. the most common tumors in descending order are lymphomas,
The two main histologic forms of iridociliary adenomas/carcino- histiocytic sarcomas, hemangiosarcomas, respiratory (nasal and
mas that have been described are papillary (57% of cases in one pulmonary) carcinomas, digital and oral melanomas, osteosarco-
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study) and solid tumors (43%). In the authors’ experience, these mas and SCC. In cats, the most common metastatic tumors to
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tumors often appear nonpigmented clinically, but histologically the eye are lymphomas, respiratory (nasal and pulmonary) carci-
at least some pigmented cells are present in approximately one- nomas and SCC.
half of cases. Pigmented tumors of the ciliary body may be grossly Lymphoma is the most common secondary intraocular tumor
indistinguishable from anterior uveal melanomas. Middle-aged to in the dog and cat, and ocular lesions are present in approximately
older dogs are the most commonly affected and golden and Lab- one-third of dogs with the disease. 74,79–81 Ocular lymphomas are
rador retrievers may be predisposed, for they comprised 27% of typically thought to be associated with systemic disease; however,
dogs with iridociliary epithelial tumors in one survey. Most of a recent study found that, 60% of dogs with ocular lymphomas
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these tumors appear to be benign, fairly well-delineated, some- are free of systemic disease at the time of enucleation and hence
times pedunculated, slow-growing masses that originate in the were classified as presumed solitary ocular lymphoma (PSOL).
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pars plicata of the ciliary body or the iris epithelium. 71–73 Although In this study, dogs with PSOL experienced a longer median
approximately 60% invade the uveal tract, only 21% invade the survival time (MST, 769 days) than dogs with known systemic
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sclera. Tumors that invade the sclera are typically classified as involvement (MST of 103 days). Histiocytic sarcomas account
adenocarcinomas and have anaplastic features, but metastasis is for 1.5% of all canine tumor submissions in the COPLOW data-
uncommon and occurs late in the course of the disease, if at all. 71– base. In dogs, the diagnosis of ocular histiocytic sarcomas carries
75 A small series of truly malignant pleomorphic adenocarcinomas a poor prognosis with rapid progression of systemic disease and