Invasion of the anterior segment by retinoblastoma is a well recognized if not very common complication, and in that it may simulate ocular inflammation it is a significant source of misdiagnosis.
Rarer diffuse infiltrating growth patterns have been reported where the retina may appear clinically normal despite tumor growth infiltration of the anterior chamber, including the iris.
Affected dogs usually present with visual deficits and presence of blood in the anterior chamber.
Ophthalmoscopy usually reveals the presence of a hemorrhagic mass in the posterior chamber.
Imaging studies, particularly CT and MRI may be required to determine metastatic involvement of the central nervous system.
Diagnosis is based on histological examination of enucleated material, with characteristic Flexner-Wintersteiner rosettes. These tumors show strong immunoreactivity with S-antigen and glial fibrillary acidic protein.
Topical corticosteroid ointments and systemic prednisolone may temporarily alleviate edema associated with this tumor, but enucleation is usually recommended.
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