Page 697 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

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Ocular Tumors

PAUL E. MILLER AND LEANDRO B.C. TEIXEIRA

Tumors of the eye, orbit, or adnexa can have devastating conse- Melanomas often occur in dogs with a pigmented conjunctiva and
quences for an animal’s vision, appearance, and comfort and may are the most common malignant tumor of the canine conjunctiva,
be harbingers of potentially life-threatening disease elsewhere in making up 16% of conjunctival tumor biopsies. Older (mean =
the body. By virtue of their location, even benign ocular tumors 11 years), female, Weimaraner, and possibly German shepherd/
6
may cause blindness and loss of the eye. Although these tumors large-breed dogs may be predisposed to conjunctival melanomas.
reportedly affected only 0.87% of all dogs and 0.34% of all cats Melanomas also have a propensity for the nictitating membrane
6,7
recorded in the Veterinary Medical Database (VMDB) over a 10- and superior palpebral conjunctiva. Ocular viral papillomas
year period, their actual frequency is undoubtedly greater because compose about 3% of conjunctival tumors and tend to occur in
many presumably benign ocular tumors are not histologically ex- young dogs and are believed to have a papillomavirus etiology
8
amined. Additional insights into the relative frequency of ocular (perhaps canine oral papillomavirus). However, one study failed
tumors can also be gained by reviewing submissions over several to identify papillomaviral genetic material in older dogs with
decades to the large ophthalmic pathology database compiled smaller solitary lesions, suggesting that the cause of ocular sur-
9
by the Comparative Ocular Pathology Laboratory of Wisconsin face papillomas in dogs may be heterogeneous. Canine squamous
(COPLOW) (Fig. 32.1). This chapter describes the more com- papilloma is a benign papillary tumor of unknown etiology and
mon ocular tumors in small animals and also uses the database makes up 9% of conjunctival tumor biopsies. Reactive papilloma
of the COPLOW laboratory to estimate the relative frequency of is seen secondary to other conditions such as meibomian tumors,
various ocular tumors. but they make up 18% of conjunctival tumor biopsies. Corneal
tumors have a predilection for the limbus.
Tumors of the Eyelids, Third Eyelid, Pathology and Natural Behavior
Conjunctiva, and Ocular Surface Sebaceous or meibomian gland adenomas and epitheliomas, pap-
Incidence and Risk Factors illomas, and melanomas comprise more than 80% of canine eyelid
and conjunctival neoplasms, and a substantial majority of these
1,2
Benign adenomas and melanomas of the haired skin or eyelid tumors are histologically benign. Even histologically malignant
margin make up 76% of canine eyelid tumors in the COPLOW eyelid tumors in dogs rarely metastasize, although they are more
1,2
database and tend to affect old dogs. One study suggests Boxers, likely to be locally invasive and recur after surgery. In contrast,
collies, Weimaraners, cocker spaniels, and springer spaniels are at most feline eyelid and ocular surface tumors such as SCC are
greater risk for eyelid neoplasia than the general hospital popula- malignant. 3
1
tion, and another study suggests that beagles, Siberian huskies, Viral papillomas tend to be well demarcated and superficial,
2
and English setters are at greater risk than mixed-breed dogs. minimally altering deeper tissues. Surgical manipulation has occa-
Canine juvenile histiocytomas affect the eyelid skin of young sionally been associated with dispersal of papillomas through-
1,2
to middle-aged dogs but are relatively uncommon, compris- out the ocular surface. 10,11 Papillomas, like histiocytomas, often
ing only 3% of eyelid biopsy samples submitted to COPLOW. spontaneously regress in young dogs, although they may persist
Squamous cell carcinoma (SCC) comprises up to two-thirds of in the older dog where they may not be of viral origin. SCC may
feline eyelid and third eyelid tumors and has a predilection for also develop superficially, but after malignant transformation the
3
the lower eyelid and medial canthus of white cats. Ocular SCC preinvasive actinic plaque can invade deeper tissues. SCC may
is less frequent in dogs, but in both cats and dogs increased expo- spread to regional lymph nodes late in the course of the disease
sure to solar radiation, lack of adnexal pigmentation, and possibly and uncommonly distantly metastasize. SCC of the third eyelid
chronic ocular surface irritation are believed to be predisposing may more readily invade the orbit than corneal or eyelid SCC.
factors (Fig. 32.2). 1,4,5 Primary corneal SCC is more common in brachycephalic dogs
Vascular endothelial cell tumors of the lateral limbus or the and has been reported to be associated with chronic keratitis and
leading edge of the third eyelid constitute 25% of conjunctival topical immunosuppressive therapy. 12
tumors in dogs and tend to occur in the nonpigmented conjunc- Adenocarcinomas of the gland of the third eyelid constitute
tiva in Bassett hounds, springer spaniels, and beagles (Fig. 32.3). 12% of conjunctival tumors in dogs and approximately 85% of

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