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Optic nerve astrocytoma in a dog
Piñyero, Pablo E.
Zimmerman, Kurt L.
Herring, Ian P.
Rossmeisl, John H.
Jortner, Bernard S.
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Intraocular neoplasms in dogs are uncommon in comparison with other anatomic locations [1–4]. Over 75% of these cases are attributed to melanocytic neoplasia . A majority of the remaining cases (~22%) are comprised of lymphoma, metastatic neoplasia, iridociliary epithelial tumors, optic nerve meningiomas, and histiocytic sarcomas in decreasing order of frequency [1, 2]. Rarely, optic nerve astrocytomas have been reported in humans, dogs, and horses [5–7]. In humans, astrocytomas involving the optic nerve are uncommon accounting for only about 1% of neoplasms at this site in comparison with 25% of neoplasms occurring in the brain [5, 8–14]. Most of these neoplasms occur unilaterally, are benign, and arise in children under 10 years of age; those involving the cerebellum have a more favorable prognosis [8, 14]. These younger patients commonly have an underlying familiar disorder such as neurofibromatosis. In older patients in their fourth and fifth decade of life, astrocytomas more commonly involve the cerebrum with a less favorable prognosis and can be associated with familiar disorders such as Li–Fraumeni syndrome [13, 15–17]. Most canine ocular astrocytoma cases are sporadic and not associated with any familial disorder [1, 13, 18–21]. However, Thomas et al. demonstrated a genomic risk factor associated with frequency of chromosome copy number aberrations within canine brain astrocytomas and tumor grade . Similar to humans, canine astrocytomas account for less than 1% of ocular and optic nerve neoplasms and 10–36% of primary intracranial neoplasms [1, 4, 16–18, 20, 21, 23]. There appears to be a breed predisposition for development of intracranial astrocytomas in English Toy Spaniels, Boston Terriers, French Bulldogs, Boxers, and English Bulldog with a peak prevalence at 7– 8 years and 1.5 odds ratio in favor of larger versus smaller breeds [13, 23]. These risk factors have not been shown in association with canine ocular forms of this neoplasm [1, 16, 17]. Gender as a risk factor has not been described for either anatomic location [1, 13, 16–18, 23]. Case reports related to ocular astrocytomas are still rare in veterinary literature. The purpose of this report is to add to this sparse body of information. This report presents the clinical, histological, and immunohistochemical features of an optic nerve astrocytoma in a dog.