Page 700 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

678 PART IV Specific Malignancies in the Small Animal Patient

second or third time if complete regression is not achieved after
the first session. Substantial postoperative swelling and usually
transient depigmentation of the frozen tissue are to be expected.
VetBooks.ir conjunctival hemangiosarcomas, melanomas, and nictitans ade-
Tumors involving the conjunctiva and third eyelid (especially
nocarcinomas) are most effectively treated by surgical excision,
occasionally to the point of exenterating the orbit. If the globe is
to be spared, however, excision of the entire nictitans should not
be taken lightly because undesirable sequelae such as ocular drying
and chronic keratitis frequently result. Bulbar conjunctival tumors
move freely and, if small, are generally amenable to excision under
only topical anesthesia and perhaps sedation. Cryosurgery may
permit the nictitans to be spared in the cases of papillomas and
early SCC, or it can be used as an adjunct to excision in advanced
canine conjunctival melanomas and SCC. 6,28
Superficial keratectomy/sclerectomy is preferred for many
corneal and scleral tumors, although some tumors require a full-
thickness resection of the cornea or sclera. In the latter case, cor-
neal or scleral allografts or autologous tissue grafts should be used • Fig. 32.4 Epibulbar melanomas typically originate from the superior lim-
to maintain ocular structural integrity. Limbal SCC and epibulbar bal region of the globe. (Image courtesy Dr. Elizabeth Adkins.)
melanoma may also be amenable to cryosurgery, although the ice
ball should be carefully monitored to avoid unnecessary freezing local corneal invasion, epiphora, and mild conjunctival irritation
of intraocular structures. may be seen. 32,33 Differential diagnoses include conjunctival
melanoma, invasive uveal melanoma, metastatic melanoma, and
Prognosis staphyloma or coloboma. Gonioscopy aids in differentiating inva-
sive intraocular tumors from limbal melanomas.
The prognosis for most canine primary eyelid tumors is excellent, Therapy should be considered if the tumor has invaded the
whether treated by excision or cryosurgery. Metastasis is rare, even eye or if growth is rapid. Given its benign nature and usually
in histologically malignant primary lid tumors, and recurrence slow growth rate (imperceptible growth over 18 months has been
rates are low (approximately 10%–15%). New primary eyelid described), observation alone may be appropriate in older dogs.
2
tumors are not uncommon and must be distinguished from recur- If intervention is required, lamellar keratectomy/sclerectomy
rence. Because most eyelid tumors in cats are malignant, the prog- with graft placement is often curative. 36–38 Beta-irradiation and
nosis is not as good as that for dogs, but it is unclear how prognosis cryosurgery have been used as adjuncts to surgery. 36,39 Cryosur-
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correlates with the histologic features. Conjunctival melanomas gery alone or laser photocoagulation has also been described as
and nictitans adenocarcinomas frequently recur after partial exci- effective means of treatment. Regrowth after local surgical exci-
sion of the nictitans, even if all the clinically visible tumor has sion occurs in approximately 30% of patients, but 2 to 3 years
6
been removed. Conjunctival hemangiosarcomas appear to have may pass before the anterior chamber is invaded and enucleation
a good prognosis because total excision may be curative, although is required. 30,32,33 The addition of adjunctive therapy such as
recurrence and loss of the eye is still possible. 15–19 Conjunctival cryotherapy or beta-irradiation substantially reduces the risk of
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MCTs also appear to have a good prognosis. recurrence after local excision. 36,39 Enucleation is curative and
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indicated if painful intraocular disease is present.
Limbal (Epibulbar) Melanomas
Limbal melanomas are typically benign, slightly raised, heavily Primary Ocular Tumors
pigmented masses originating from melanocytes in the sclera or
subconjunctival connective tissue (Fig. 32.4). 29–35 They comprise Canine Anterior Uveal Melanomas
3.5% of all canine ocular tumors and 1% of feline ocular tumor Incidence and Risk Factors
submissions to COPLOW. The majority of these slow-growing In one review of data from the Armed Forces Institute of Pathol-
tumors originate in the superior limbal region, suggesting expo- ogy, intraocular melanomas, other primary intraocular tumors,
sure to solar radiation may be a risk factor. Affected dogs aver- and metastatic intraocular neoplasms constituted 12%, 14%, and
15
40
age 5 to 6 years old (cats 8+ years), and a female sex and German 9%, respectively, of canine ophthalmic/orbital/adnexal tumors.
shepherd, golden retriever and Labrador retriever breed predilec- In the COPLOW archive, uveal melanocytic tumors make up
tion has been inconsistently reported. 29–35 Confirmed metastasis 25% of all ocular tumor submissions. Any age is at risk, but most
has not been reported in dogs or cats and mitotic figures are rarely affected dogs are older than 7 years of age, and breed or sex predi-
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encountered; although in one study, two of four cats also had lections are inconsistent.
feline leukemia virus (FeLV)-associated lymphoma or leukemia,
and a third cat had a second intraocular pigmented mass unas- Pathology and Natural Behavior
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sociated with the limbal tumor. Lightly pigmented spindle cells Approximately 75% of canine intraocular melanomas are benign,
capable of division are seen histologically, but the dominant cell and 95% arise from the iris or ciliary body (Fig. 32.5). 30,32,41 The
is presumably a hypermature spindle cell that is large, round, pig- most clinically useful classification scheme classifies these tumors
ment laden, and benign. These masses are often only inciden- simply as melanocytoma (benign) and melanoma (potentially
30
tally noted and the clinical signs are typically minimal, although malignant) based on nuclear features of the tumor cells, with