Idiopathic sclerosing orbital pseudotumor in seven cats

Abstract

Clinical findings and histopathology of globes and orbital tissues in cats bore many similarities to idiopathic sclerosing orbital pseudotumor in humans. In cats, the prognosis for the globe appears to be poor but an elucidation of the pathogenesis and earlier diagnosis coupled with more aggressive treatment modalities as indicated in humans may be beneficial.

Idiopathic sclerosing orbital inflammation mimicking a malignant spindle cell tumor in a dog

“…The spindle cell proliferation expanded and effaced the retrobulbar soft tissue and skeletal muscle. Together with lymphoplasmacytic infiltration and a prominent reactive fibroblastic profile, the aggressive nature of this mass was consistent with a malignant spindle cell tumor, a sclerosing form of idiopathic orbital inflammation (ISOI) or an inflammatory myofibroblastic tumor (IMT) 1, 2, 3. Given the sparcity of literature describing IMT in the dog, the absence of any reports describing ISOI in this species, and the distribution of the lesion, the most likely histological diagnosis was malignant peripheral nerve sheath tumor.…”

“…However, a few early reports in this species did describe a relatively extended survival time alongside immunosuppressive treatment 13, suggesting one or more of the following: (1) that a less aggressive subtype exists, (2) that patient‐derived factors modify disease progression and/or therapeutic response, or (3) that FROMS and feline IOI are two separate disease entities. The course of FROMS resembles the clinical history of the dog, with insidious exophthalmos and progressive lack of globe mobility 1, 3. Neither FROMS nor IOI are reported to metastasize – however, they exhibit divergent microscopic features.…”

“…Such disorders occur infrequently in animals and include immune‐mediated conditions and idiopathic orbital inflammation (IOI; otherwise known as orbital pseudotumor) 1, 2, 8. We consider that the term “pseudotumor” is less than ideal for these orbital inflammatory growths – we have thus adopted the most recent nomenclature from the human literature to promote cohesive cross‐translational understanding of the pathology while awaiting a more refined classification in companion species.…”

“…Descriptions of orbital pseudotumor in the veterinary literature, however, include only one prosimian primate and a lacrimal pseudotumor in a bull terrier 26, 27. Feline lesions originally recorded as orbital pseudotumor have since been reclassified as feline restrictive orbital myofibroblastic sarcoma (FROMS) owing to their highly aggressive nature, resulting in bilateral exenteration and/or euthanasia in all reported cases 1, 3, 28, 29. However, a few early reports in this species did describe a relatively extended survival time alongside immunosuppressive treatment 13, suggesting one or more of the following: (1) that a less aggressive subtype exists, (2) that patient‐derived factors modify disease progression and/or therapeutic response, or (3) that FROMS and feline IOI are two separate disease entities.…”

“…Neither FROMS nor IOI are reported to metastasize – however, they exhibit divergent microscopic features. Feline restrictive orbital myofibroblastic sarcoma displays a mixed inflammatory response with perivascular cellular infiltrate and fibrous tissue spreading along fascial planes 1. Mild fibroblastic pleomorphism without mitotic figures and positive immunohistochemistry for S100, smooth muscle actin and vimentin (with or without glial fibrillary acidic protein) are additional characteristic features not seen in the canine mass 1, 28.…”