Page 698 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

676 PART IV Specific Malignancies in the Small Animal Patient

13
all third eyelid tumors in dogs and cats. They are variable in possible. 13–15 Adenomas of the gland of the third eyelid are less
13
morphology and often show moderate infiltrative growth. They frequently reported in dogs (approximately 14% of all third eyelid
tumors) as are SCC (approximately 1% of all canine and 16% of
may mimic prolapse of the gland of the nictitans (“cherry eye”)
VetBooks.ir by appearing as localized, firm, smooth, pink swellings on the all feline third eyelid tumors). 13
The natural behavior of conjunctival vascular, melanocytic,
posterior surface of the nictitans, but a key differentiating feature
is their occurrence in much older dogs (10–16 years). Although and mast cell tumors (MCTs) is poorly understood, in part
excision of the grossly visible tumor may initially appear adequate, because they are uncommon. Conjunctival hemangiomas and
recurrence is common if the entire gland is not removed, and hemangiosarcomas tend to remain relatively superficial but may
metastasis, especially to the regional lymph nodes and orbit, is recur after simple excision. 15–19 Hemangiosarcomas may exhibit
a more aggressive course and a primary ocular hemangiosarcoma
must be differentiated from a metastatic lesion. However, metas-
Anatomic Distribution of Canine Primary Ocular Neoplasms (n = 11091)
tasis of primary conjunctival vascular tumors, even when classified
Orbit as hemangiosarcomas, appears to be rare. 15–19
Conjunctiva Feline conjunctival melanomas originate on the bulbar con-
junctiva and invade the eyelid. 20,21 Melanoma of the conjunctiva
in dogs is most often morphologically malignant, but metastatic
disease is not common. As in cats, canine conjunctival melanomas
have been reported to recur locally after surgical excision in 55%
of cases, and at least 17% of the dogs experienced orbital invasion
Eyelid Globe or spread to the regional lymph nodes or lungs. Melanomas origi-
6
nating from the palpebral conjunctiva may have greater metastatic
6
potential. Mitotic index, cell type, and degree of pigmentation
are not useful predictors of malignancy for canine conjunctival
A melanomas. Conjunctival (subconjunctival) MCTs make up 4%
6
of conjunctival tumors, but their natural history is poorly under-
Anatomic Distribution of Feline Primary Ocular Neoplasms (n = 4631) stood in part because they are uncommon. Nevertheless, they have
Eyelid been suggested to have a relatively benign course in dogs, even
Orbit with incomplete excision and if the tumors present more malig-
Conjunctiva nant histologic features. 22,23 Conjunctival MCTs are not typically
graded as the grading system was developed for cutaneous tumors
and the criteria are not applicable to conjunctival tissues. In the
largest review to date, local recurrence was observed in only 2 of
32 dogs, even though residual tumor was histologically present in
25 dogs. In addition, none of the 32 dogs died of conjunctival
23
23
Globe MCT-related disease.
History and Clinical Signs
B
Vascular tumors are often focal, raised, soft, red masses with vis-
• Fig. 32.1 The distribution of canine (A) and feline (B) ocular tumors sub- ible feeder vessels arising from the surface of the conjunctiva or
mitted to the Comparative Ocular Pathology Laboratory of Wisconsin. third eyelid. 15–19 SCC of the eyelid, third eyelid, or ocular surface

A B
• Fig. 32.2 (A) Squamous cell carcinoma affecting the lower eyelids of a boxer. (B) Same dog after cryosur-
gical ablation of the tumor. Lid function is spared.