As in the canine species, intraocular tumours are relatively frequent also in felines. These tumours can be primary or metastatic, unilateral or bilateral. Clinically, they can occur as organized neoformations or with non-specific signs of uveitis, or with a combination of both. Clinical signs resulting from the complications of uveitis, such as haemorrhages, retinal detachment and glaucoma, are often present. In the metastatic forms of intraocular tumours systemic signs of the primary malignancy may also be present.
PRIMARY INTRAOCULAR TUMOURS
- Melanoma
- Diffuse iris melanoma
- Atypical anterior uveal melanoma
- Limbal melanocytoma
- Post-traumatic ocular sarcoma
- Ciliary body tumours
- Adenoma/adenocarcinoma
- Spindle cell iris tumour
Diffuse iris melanoma
Diffuse iris melanoma is the most common primary neoplasm in the feline species. It is almost exclusively unilateral and presents as a pigmented lesion, which may initially be isolated, or more frequently as multiple, small pigmented areas on the surface of the iris (Fig. 1). With time, these lesions tend to increase in colour intensity and size as they often have the tendency to coalesce (Fig. 2). The tumour originates from the anterior part of the surface of the iris and then tends to infiltrate under the surface, altering the stromal architecture, the shape of the pupil (dyscoria) and increasing the thickness of the iris itself. Finally, the lesion tends to extend to the iridocorneal filtration angle, with the consequent frequent onset of secondary glaucoma (Fig. 3). The pigmented cells which are characteristic of these lesions have a limited capacity for cohesion and with time tend to exfoliate into the aqueous humor in the anterior chamber, and secondarily tend to infiltrate the drainage tracts, involving the scleral venous plexus, with a consequent possible spread to internal organs (spleen and lungs). Metastatic spread may take place even some years after the recognition of the disease (and eventual enucleation of the eye): the metastatic rate is not currently known, although some authors claim that it is about 50-63%. The mean age at tumour onset is around 11 years (range, 4-20 years). There is no predilection for gender, breed or age. One case of amelanotic diffuse iris melanoma has been described.
The treatment of choice is enucleation although the decision to operate is often extremely complex, especially in the initial stages, because of the diagnostic difficulties that force the clinician to ponder on whether to intervene and, if so, when. The decision in favour of radical surgery may be justified by the presence of a marked increase in the colour of the iris, with coalescence of the pigmented areas, by thickening of the stroma of the iris whose surface acquires a powdery appearance, by the presence of dyscoria, iris ectropion, uveitis not responsive to treatment, glaucoma, involvement of the ciliary body and by extension to the sclera.
Atypical anterior uveal melanoma
This is a rare, highly metastasising tumour, which tends to involve secondarily the anterior uvea and the iris; it probably originates from the posterior segment (choroid) and also infiltrates the subretinal space. From a clinical point of view the initial symptoms are those of the complications resulting from the intraocular growth of the tumour, such as secondary glaucoma and buphthalmos. In some cases there can be increased pigmentation and thickening of the iris, but more frequently there is a markedly pigmented, intraocular, multifocal neoformation which tends to infiltrate and extend beyond the sclera. The treatment of choice is enucleation.
Limbal melanocytoma
This is a neoplasm with an extremely low incidence (around 3% of melanocytic tumours according to some authors), characterized by the presence of a pigmented lesion, occasionally raised, with irregular margins, which may partially extend to the cornea, where it can give rise to a secondary lipid keratopathy. The neoformation is typically located in the dorsolateral quadrant of the sclera (Fig. 4). The diagnosis can be made clinically, with the aid of a biomicroscope. Gonioscopy and ultrasonography are important instrumental examinations, which are helpful for the differential diagnosis in order to distinguish limbal melanocytomas from conjunctival melanoma, extrascleral extension of a uveal melanoma or atypical uveal melanoma. The biological behaviour of limbal melanocytoma is substantially benign, and metastases are rare. Treatment consists of surgical excision, which may be followed by local treatment with cryotherapy and laser photocoagulation. In some cases a cartilage graft of the third eyelid or a graft with biosynthetic material may be combined with the surgical resection in order to repair the corneoscleral defect.
Post-traumatic ocular sarcoma
Post-traumatic ocular sarcoma is the second most frequent primary ocular neoplasm in the cat, after diffuse iris melanoma. This tumour has an extremely malignant behaviour and tends to spread by continuity and contiguity to the orbital tissues or through the optic nerve. A common denominator in the clinical history of cases of ocular sarcoma is previous ocular trauma or protracted inflammation. The latency period between the triggering episode and the overt clinical manifestation of the neoplasm can be extremely long in some cases (up to 12 years with a mean period of around 5 years). The age at onset of the tumour varies between 7 and 16 years of age. Clinically, the neoplastic tissue (pinkish-white neoformations) can be seen: it may involve all of the components of the eyeball, it may infiltrate the sclera and it may extend beyond it, involving the peripheral nervous tissue and the optic nerve, apart from, as previously mentioned, the orbital tissues. A clear view of the lesions is very often prevented by the concomitant presence of corneal oedema, inflammation and intraocular haemorrhages. In some cases the presenting clinical sign may be non-specific chronic uveitis [4] or glaucoma. Metastases may spread through the blood circulation or, less frequently, from the affected orbital tissues via the lymphatic system to the tributary regional lymph nodes. Histologically there is a spindle cell variant of the tumour, which accounts for about 70% of these neoplasms, a round cell variant (24%), which is thought to be a form of lymphoma, and finally a chondrosarcoma/osteosarcoma variant (6%).
There has been a long debate on the tissue of origin of post-traumatic ocular sarcoma, which is currently considered most likely to be the epithelium of the lens [9]. Factors supporting this hypothesis are that laceration of the lens capsule is frequently encountered in histopathological studies of these tumours, in early forms there are often neoplastic cells around the lens, and finally, in some areas of these tumours there is a basal membrane, similar to that of the lens capsule, around the neoplastic cells.
In view of the marked aggressiveness of this tumour, enucleation and exenteration of the orbit must be done as early as possible. Given the aetiopathogenesis of this tumour, careful, frequent and repeated assessments must be made of blind eyes which present chronic uveitis, phthisis bulbi, sequelae of post-traumatic lesions or post-traumatic glaucoma.
Ciliary body tumours: adenomas and adenocarcinomas
In order of frequency, ciliary body tumours come behind diffuse iris melanoma, lymphoma and post-traumatic sarcoma. These tumours are not common in cats; when present they can affect the ciliary bodies or the iris, with a tendency, during their growth, to luxate or subluxate the crystalline lens [9]. The mean age of tumour onset is around 9 years, with no gender or breed predilection. From a clinical point of view these tumours may present as non-pigmented masses, which infiltrate the ciliary bodies and the posterior and anterior chambers. Frequently, however, in the early stages the complications from such tumours, such as anterior uveitis, intraocular haemorrhages and glaucoma, may be more evident clinically. The suggested treatment is enucleation.
METASTATIC INTRAOCULAR TUMOURS
- Lymphosarcoma
- Adenocarcinoma
- Haemangiosarcoma
- Extramedullary plasmacytoma
- Squamous cell carcinoma
- Angioinvasive pulmonary carcinoma
- Fibrosarcoma
Lymphosarcoma
Lymphosarcoma is the most common secondary tumour in the cat, and in absolute terms it is the second most common feline intraocular tumour. It can be unilateral or bilateral and most frequently affects the anterior uvea, where it is present as a nodular infiltration or in a diffuse form. Frequently, there is only an inflammatory reaction, caused by the intraocular manifestation of the disease, which can mask the nodular and infiltrative forms (Fig. 5). Localisation to the posterior uvea is less frequent, and is manifested by retinaldetachment, chorioretinitis and retinal and/or vitreous haemorrhages. Other structures which may be involved are the corneal limbus, the adnexae, peripheral nervous tissue and the optic nerve. The mean age of onset is about 8 or 9 years. There is no gender or age predilection. No relation has been found between this lymphoma and positivity for Feline leukemia virus and Feline immunodeficiency virus, although cats with lymphoma which are positive for the retrovirus very frequently have diseases associated with the lymphomatous state and shorter survival than unaffected cats. Ocular lymphoma is considered a form of multicentric lymphoma and the ocular form often precedes the clinical signs of the systemic disease. Apart from the clinical signs, the diagnosis may be based on an invasive intraocular biopsy, on cytology of the aqueous humor and finally on histopathology.
Systemic therapy is based on appropriate chemotherapy protocols, while topical therapy consists of corticosteroids combined with an antibiotic, atropine 1% in order to prevent synechiae and adhesions, and pressure-lowering drugs if secondary glaucoma occurs.
Other metastatic neoplasms
Other metastatic neoplasms described in the feline species are adenocarcinoma, originating from the mammary glands or from the uterus, haemangiosarcoma, extramedullary plasmacytoma, squamous cell carcinoma, angioinvasive pulmonary carcinoma and fibrosarcoma. From a clinical point of view also in these cases the signs may be unilateral or bilateral, with the presence of an infiltrating mass or a non-specific form of uveitis which is more frequently localised in the posterior segment, where it is manifested by retinal haemorrhages and detachment, and the characteristic presence of wedge-shaped areas of discoloration and attenuation of the blood vessels.
Suggested readings
- Plummer CE, Kallberg ME, Ollivier FJ, Gelatt KN, Brooks DE. Use of a biosynthetic material to repair the surgical defect following excision of an epibulbar melanoma in a cat. Vet Ophthalmol. 2008 Jul-Aug;11(4):250-4.
- Betton A, Healy LN, English RV, Bunch SE. Atypical limbal melanoma in a cat.J Vet Intern Med. 1999 Jul-Aug;13(4):379-81.
- Sullivan TC, Nasisse MP, Davidson MG, Glover TL. Photocoagulation of limbal melanoma in dogs and cats: 15 cases (1989-1993). J Am Vet Med Assoc. 1996 Mar 15;208(6):891-4.
- Day MJ, Lucke VM. Melanocytic neoplasia in the cat.J Small Anim Pract. 1995 May;36(5):207-13.
- Dubielzig R.R. (1990): Ocular neoplasia in small animals. Vet.Clin.North Am. Small Anim.Pract., 20, 3, 837-848.
- Dubielzig RR, Steinberg H, Garvin H, Deehr AJ, Fischer B. Iridociliary epithelial tumors in 100 dogs and 17 cats: a morphological study. Vet Ophthalmol 1:223 –231,1998
- Peiffer RL. Ciliary body tumours in the dog and cat; a report of thirteen cases.J Small Anim Pract 24:347 –370,1983