A 10 yr old female spayed Pomeranian presented with a history of dyspnea and coughing and was diagnosed with a cranial mediastinal mass presumed to be a thymoma. Surgical removal was elected and occurred without intraoperative complications. Histopathology revealed the lesion to be a cholesterol granuloma. The patient developed a brief period of increased respiratory difficulty 3 days postoperatively. Thoracic radiographs showed mild pleural effusion and the patient improved with supportive care. Five months postoperatively, repeat thoracic radiographs revealed no evidence of recurrence or respiratory pathology. This case report describes a cholesterol granuloma in a unique location and reviews the pathogenesis/pathophysiology of this type of mass.