Feline Ocular Neoplasia

Chapter 258


Feline Ocular Neoplasia




Ocular neoplasia is less common in the cat than in the dog, but the proportion of primary tumors that are malignant is much higher. For appropriate therapeutic intervention, it is important to distinguish primary tumors from secondary neoplasms. Staging of disease also is important, and the concepts applicable to the cat are discussed in the chapter on canine ocular neoplasia (see Chapter 257) in this section. Treatment of many ocular neoplasms is surgical, and complications of surgery, including scarring, can lead to a number of problems of the globe or adnexa. Thus optimal surgical outcomes are most likely when the procedure is performed by a specialist in ophthalmic surgery. Additionally, other treatments may involve advanced oncologic therapies that can be obtained only by referral.



Primary Ocular Neoplasia



Adnexa


Feline eyelid neoplasms are less common and more likely to be malignant than similar neoplasms in dogs. Virtually any epidermal or dermal tumor may affect the eyelid. The most commonly reported neoplasm is squamous cell carcinoma. Other tumors include fibrosarcoma, adenocarcinoma or adenoma, mast cell tumor, basal cell tumor, fibroma, papilloma, hemangiosarcoma, and melanoma. Large eyelid tumors require extensive reconstructive surgery after resection, which may deter owners from pursuing treatment. Because malignant eyelid tumors can result in death or euthanasia of the cat, it is best to examine and treat these tumors early in the course of disease.


Squamous cell carcinomas may appear as ulcerated or proliferative, pink, cobblestone masses. They are more common in older cats with lightly pigmented (pink) eyelid margins. Exposure to ultraviolet light is a significant risk factor for the development of squamous cell carcinoma. Squamous cell carcinoma is locally invasive and tends to metastasize late in the course of disease. The treatment of choice is complete surgical excision, although this may be challenging with large or multifocal lesions. Adjunctive therapies, including beta irradiation (using a strontium 90 probe) or cryotherapy can successfully induce remission in some patients with small tumors. If complete surgical excision is unattainable and adjunctive therapies are not available, enucleation or exenteration may be necessary. Piroxicam 0.3 mg/kg q48h PO is an empirical treatment for some cats with squamous cell carcinoma, but the patient must be closely monitored for nephrotoxicity and gastrointestinal ulceration as well as for efficacy.


Feline periocular peripheral nerve sheath tumor appears clinically as a firm intradermal mass with little to no alopecia or surface ulceration. Surgical resection with wide margins is recommended, and reconstructive surgery may be required to maintain eyelid function. Enucleation, with creation of rotational flaps to cover the orbital wound, may be necessary to prevent recurrence.


Apocrine gland hidrocystomas are an unusual type of benign neoplasia seen most commonly in aged brachycephalic cats. The clinical appearance is that of multiple 2- to 8-mm smooth, round, darkly pigmented masses that contain a brown serous fluid. Although the masses are benign, their rupture may be associated with ocular discomfort. Surgical excision alone is associated with recurrence. Topical application of trichloroacetic acid and cryoablation have been reported to be more effective therapies in preventing reappearance.


Neoplasia uncommonly affects the feline nictitans. Clinical signs include elevation of the nictitans, mass effect with deviation of the globe, conjunctivitis, and enophthalmos or exophthalmos. The most commonly reported tumor is squamous cell carcinoma, which may be a local extension from an eyelid or palpebral conjunctival lesion. Other reported tumors include adenocarcinoma, mast cell tumor, hemangiosarcoma, fibrosarcoma, lymphoma, and melanoma. Care must be taken to differentiate prolapse of the gland of the nictitans (also called cherry eye), a relatively uncommon condition in cats except for the Burmese and Bombay breeds, from neoplasia of the nictitans. Surgical excision is indicated for most neoplasms, with exenteration necessary when adequate surgical margins cannot be achieved with the globe in situ.



Cornea and Conjunctiva


Primary corneal neoplasia is uncommon in the cat. The limbus is the most frequently affected region of the cornea. Limbal or epibulbar melanoma is the most commonly recognized tumor of the feline limbus. Limbal melanomas arise from the pigmented melanocytes of the limbus and sclera. The clinical appearance is that of a black, smooth, well-circumscribed mass that may be observed to invade the cornea and sclera. Gonioscopy is useful to detect extension into the iridocorneal angle, and high-resolution (35- to 50-MHz) ultrasonography may be necessary to determine the extent of intraocular involvement. Because limbal melanomas in cats generally are benign and nonpainful, monitoring alone is indicated in most cases. If progression is noted, treatment options include surgical debulking and adjunctive treatment of the tumor bed (diode laser ablation, cryoablation, beta irradiation) or full-thickness surgical excision with grafting to restore scleral integrity. Digital photographs and detailed measurements are useful for detecting subtle changes in size and shape. Although distant metastasis of limbal melanoma has been reported, it is rare.


Other primary corneal tumors include squamous cell carcinoma, hemangiosarcoma, fibrous histiocytoma, and lymphoma. All would be expected to arise at the limbus and usually involve corneal neovascularization. Careful clinical examination and diagnostic cytologic examination or biopsy are required to differentiate these uncommon corneal neoplasms from the more common feline corneal diseases of eosinophilic keratitis or feline herpesvirus 1–associated keratoconjunctivitis. Keratectomy with adjunctive radiation therapy or cryotherapy is indicated for these primary corneal neoplasms.


Unlike limbal melanomas, conjunctival melanomas are more likely to be malignant and are associated with a higher rate of metastasis. Golden to brown granular pigmentation of the temporal bulbar conjunctiva, palpebral conjunctiva, and eyelid margin is a common ocular finding in cats with an orange coat and must not be confused with a conjunctival melanoma. Conjunctival melanomas typically are dark brown or black and raised. The palpebral, bulbar, or nictitans conjunctiva may be affected. Although excision and adjunctive treatment, including irradiation or cryoablation, may be effective in treating local disease, widespread metastasis still may result within weeks to months. Local recurrence may follow simple excision.


Primary conjunctival hemangiomas and hemangiosarcomas are diagnosed rarely. Their biologic behavior is locally aggressive with rare metastasis. Complete excision is recommended. A single report of B-cell lymphoma with the clinical manifestation of palpebral conjunctival masses suggests that the conjunctiva may be primarily involved in rare cases of lymphoma.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Feline Ocular Neoplasia

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