Computed tomography findings of peritoneal tumour in the absence of primary lesions: preliminary study

Primary peritoneal tumours are uncommon and include mesothelioma and carcinoma. Mesothelioma identification is challenging, as there are no established rapid diagnostic methods. In the absence of a simple means of diagnosis, evaluation often requires several invasive biopsies, highlighting the need to develop a definitive diagnostic method. To address this, we focused on identifying characteristic computed tomography (CT) findings of primary peritoneal tumours. This study retrospectively assessed CT findings of peritoneal tumours in the absence of primary lesions elsewhere, including four carcinomas, five mesotheliomas, and three lymphomas in five dogs and seven cats. Whole-body contrast-enhanced CT was performed with data obtained on peritoneal tumour location, shape, contrast enhancement patterns during the arterial, portal and equilibrium phases, lymphadenopathy, ascites, calcification and attenuation values of peritoneal tumours among precontrast and postcontrast images. For carcinomas, 25% of cases were located in the visceral region and 75% in both parietal and visceral regions. All cases of mesothelioms were identified in the parietal region, while 80% were identified on the diaphragm. For Lymphomas, 67% of cases were located in the parietal region and 33% of cases in the visceral region. Location was a characteristic feature, showing significant differences among tumours (P = 0.006). Among tumours, no significant differences were observed for tumour shape, contrast enhancement patterns, lymphadenopathy, ascites and calcification. For mesothelioma, the attenuation value was significantly high in the portal and equilibrium phases images compared to precontrast images (P = 0.04). Thus, tumour location and attenuation value may assist in differentiating peritoneal tumours.