Retrobulbar Cryptococcoma Mimicking Tumor in a Labrador Retriever

Abstract

Background: Cryptococcosis is a systemic mycotic disease caused by encapsulated yeasts C. neoformans and C. gattii. Cryptococcus neoformans is predominantly found in soils and feces of pigeons and psittacids. Infection occurs mainly through the respiratory tract, through the inspiration of fungal propagules (basidiospores and/or desiccated yeast cells). The main lesions observed are in the nasal cavity and lungs, but in dogs, the central nervous system and eyes are widely affected. Despite some previously mentioned reports, the retrobulbar form has not been described in the literature. Therefore, the purpose of this report is to describe a case of retrobulbar cryptococcoma mimetizing a tumor in a young bitch.  Case: A 2-year-old female Labrador Retriever,  was admitted to one Veterinary Hospital with exophthalmia on the left eye for 15 days and other signs included negative retropulsion, mydriasis, and abscence of menace and pupillary reflexes. Ocular ultrasound imaging revealed a hyperecotic and heterogeneous retrobulbar mass in the mid-dorsal region compressing the optic nerve. Computed tomography of the skull showed the presence of proliferation of neoplastic tissue in a locally invasive retrobulbar region promoting      moderate rostrolateral displacement of the left ocular bulb, discrete osthelysis in maxillary bone, palatine, medial wall of the orbital bone and frontal bone, with destruction of cribiform plate adjacent to the dorsal region of the orbital wall and presence of mild contrast uptake in the region of the left olfactory bulb lobe, characterizing a picture compatible with neoplasia with malignancy and locally invasive characteristics. Exenteration and excision of part of the frontal bone were performed and histopathological examination revealed granulation with the presence of fibroblasts and  numerous typical blastoconidia of Cryptococcus neoformans. The patient was treated with Itraconazole [10 mg/kg, v.o, SID, for 90 days] and one year after diagnosis, X-ray was performed to control the lesion and radiographic aspects were within normal limits.Discussion: Cryptococcus sp. is an environmental fungus that has the potential to be pathogenic to humans and animals. Fungus present as a basidiospores in pigeon droppings. The patient described had a history of contact with free-living pigeons, making it a risk factor for the occurrence of cryptococcosis, being the possible cause of the infection. In dogs, the disease is mainly described in immunosuppressed animals, which was not the case of the patient, who presented clinical and laboratory results within the normal range and without a previous history of use of immunosuppressants. The alterations described in the computed tomography, such as destruction of the cribriform plate adjacent to the dorsal region of the left orbital wall and the presence of slight contrast uptake in the left olfactory bulb lobe region, are compatible with the main entry point for propagules of Cryptococcus sp. In the present case, no periocular and ocular alterations were observed as described in the literature, and the lesion was restricted to the retrobulbar space. Ultrasonography and computed tomography revealed a neoformation mimicking a malignant neoplasm and the diagnosis of cryptococcoma was revealed by histopathology.  Based on the present case, cytology through aspiration of retrobulbal neoformations is imperative as a diagnostic method, especially in endemic areas for fungal diseases that can mimic ocular neoplasms. Keywords: cryptococcosis, fungus, Cryptococcus sp., dog. Descritores: criptococose, fungo, Cryptococcus sp., cão.