Computed tomography-based thymoma-to-cranial intrathoracic volume ratio predicts the feasibility of video-assisted thoracoscopic surgery in a small dog: A case report.

Background: Canine thymoma (CT) is the most common neoplastic disease of the cranial intrathoracic cavity. Reports of video-assisted thoracoscopic surgery-thymectomy (VATS-T) in dogs are increasing, but the surgical indication criteria remain unclear. This report highlights the value of a new criterion called the thymoma volume to cranial intrathoracic volume ratio (T/CI ratio) for evaluating the feasibility of VATS-T. Case Description: A neutered 9-year-old Papillon weighing 3.5 kg had a mass of approximately 20 mm in the cranial intrathoracic cavity. The dog was in good general condition and had no clinical symptoms. Computed tomography revealed a solitary mass with clear boundaries and weak contrast enhancement. The T/CI ratio obtained from CT examination was 2.4%. The dog underwent thoracoscopic tumor resection. Pathological examination revealed that the tumor was a thymoma. The dog was discharged without any postoperative complications. The T/CI ratios obtained from CT data of dogs of the same breed and weight, which ranged from 1.1% to 4.1%, were calculated based on previous reports that measured the volume of thymomas. Conclusion: The T/CI ratio may serve as a new objective criterion for evaluating the relationship between cranial intrathoracic volume and thymoma volume for VATS-T, regardless of dog body size. Although this case demonstrates a promising correlation between the CT-based T/CI ratio and the feasibility of VATS-T, the findings are limited to a single case. Further studies involving a larger number of patients are necessary to validate this observation.