Limbic Tumors (Melanoma)

The following is excerpted from one of my fave sites, (Vetfolio) for my notes category. (For future reference but linked for bibliographical accuracy.)

Limbal (Epibulbar)

Limbal melanomas are the most common ocular melanomas in dogs, accounting for 20% to 50% of these tumors,17-19 and are less common in cats.7 In both species, this tumor is typically a smooth, black or heavily pigmented, subconjunctival mass ( FIGURE 3 ) that is noted incidentally by an owner or a veterinarian.20,21 These tumors usually involve the adjacent cornea and/or conjunctiva and, much less commonly, may extend intraocularly.20,21 Differentiating a tumor of limbal origin from extension of an intraocular uveal tumor into the sclera may be difficult with advanced disease. Most canine limbal melanomas are located along the superior half of the limbus, and German shepherds appear to be affected more frequently than other breeds.17,19,22

carbon dioxide laser27 energy treatment
These tumors are generally considered to be benign, and no cases of confirmed metastasis have been reported in dogs.17,19,21 However, subpopulations of cells within the tumor may display more malignant characteristics.21 The tumors tend to grow more rapidly in younger dogs and more slowly in older dogs and most affected cats.20,21 Limbal melanomas in cats are similar to those in dogs in appearance, treatment, and prognosis, although distant metastasis has been reported.7,20,23The recommended treatment of a limbal melanoma depends on the rate of tumor enlargement, extent of the tumor at presentation, and expertise of the surgeon or the possibility of referral to a specialist. Because of the benign nature of most of these tumors, small, slowly growing masses may be monitored for progression, particularly in older patients.1,21 For rapidly growing tumors, surgical resection (partial- or full-thickness sclerectomy/keratectomy) is potentially curative and may maintain a functional and cosmetic globe.19,24 Techniques for removing the mass and repairing the resultant corneoscleral defect are described elsewhere.25Additional treatment modalities have also been evaluated. Cautious application of strontium irradiation26 or Nd:YAG,17 diode, or carbon dioxide laser27 energy treatment alone or in addition to surgical debulking can be effective. Cryotherapy has also been reported as an effective component of the treatment of limbal melanomas.1,10,20 The relative success of cryosurgery in treating limbal melanomas has not been thoroughly evaluated. Enucleation can be curative but is recommended only in eyes in which the melanoma has invaded the anterior chamber, filtration angle, or uveal tract and painful intraocular disease (e.g., glaucoma, uveitis) has resulted. Determining the full extent of the tumor before surgery may require diagnostics (e.g., gonioscopy, high-resolution ultrasonography) typically performed by a specialist.
Dr Erik Johnson is a Marietta, Georgia Veterinarian with a practice in small animal medicine. He graduated from University of Georgia with his Doctorate in 1991. Dr Johnson is the author of several texts on Koi and Pond Fish Health and Disease as well as numerous articles on dog and cat health topics.