Abstract
CASE SUMMARY: This case report describes the clinical and pathological features of telangiectatic osteosarcoma (TOS) with brain invasion in a 4-year-old female domestic shorthair cat. The cat presented with respiratory distress, epistaxis, anorexia and significant nasal obstruction. A rhinoscopy revealed an amorphous white neoformation in the left nasal cavity. Despite treatment, the cat's condition deteriorated and it succumbed to the disease. Necropsy and histopathologic examination revealed an infiltrative malignant neoplasm with osteoid matrix and sarcomatous cells surrounding blood-filled non-vascular spaces. Immunohistochemistry showed positive staining for bone cell markers and vimentin, while endothelial markers were negative, confirming TOS. RELEVANCE AND NOVEL INFORMATION: Nasal diseases in cats present significant diagnostic challenges due to similar clinical signs, such as respiratory distress and nasal discharge. Nasal osteosarcomas are rare, and TOS is the rarest subtype, characterized by blood-filled spaces within an aggressive osteolytic lesion. This case highlights the diagnostic complexities and poor prognosis associated with TOS in cats, emphasizing the need for advanced imaging and immunohistochemical tests for accurate diagnosis. Given the aggressive nature and rapid progression of TOS, it should be considered in differential diagnoses of feline nasal obstructive lesions.