Unique Imaging Findings of a Calvarial Ossifying Fibroma Successfully Managed With Surgery and Definitive Intent Radiotherapy.

This case report describes a 6-year-old female neutered Boxer dog diagnosed with calvarial ossifying fibroma presenting with left-sided periocular swelling, nasal discharge, epistaxis, and subtle exophthalmos. Diagnostic investigations included serial computed tomography (CT; five studies over 14 months), ultrasound-guided needle aspiration, surgical biopsy, and CT-guided core biopsy. CT identified a well-delineated, non-mineralized, strongly enhancing expansile lesion within the orbital portion of the left frontal bone with retrobulbar tissue displacement and a lobular sinonasal mass causing unilateral turbinate destruction. Progressive mineralization of the calvarial lesion was observed on subsequent CT studies following surgery and radiotherapy. Histopathology confirmed ossifying fibroma in both components (left frontal bone and sinonasal mass). The patient received partial surgical excision followed by definitive external beam volumetric modulated arc radiotherapy (VMAT), achieving durable local control with no recurrence after more than 1 year. The patient required ongoing ophthalmological monitoring and long-term medication following VMAT.