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

Our plain-English summary of Computed tomography findings of peritoneal tumour in the absence of primary lesions: preliminary study, by T. Tanaka, M. Tomihari, T. Hasegawa (Australian Veterinary Journal, 2026).

The study

• Authors: T. Tanaka, M. Tomihari, T. Hasegawa
• Journal: Australian Veterinary Journal
• Published: 2026;104(8):532-537
• Read it: PubMed · Publisher · Free full text

Abstract

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.

© 2026 The Author(s). Australian Veterinary Journal published by John Wiley & Sons Australia, Ltd on behalf of Australian Veterinary Association.

In plain English

This veterinary study looked back at computed tomography (CT) scans of 12 pet animals, five dogs and seven cats. Each had a tumour of the peritoneum (the lining of the abdomen), and no primary tumour was found elsewhere. The animals were seen at two centres in Osaka, Japan, between 2016 and 2025. The tumours were four carcinomas, five mesotheliomas and three lymphomas. The study did not examine asbestos or any other cause of disease. Tumour location differed significantly among the three tumour types (P = 0.006). All five mesotheliomas were in the parietal peritoneum, and in four of the five the lesions were on the diaphragm. Tumour shape, contrast enhancement pattern, lymphadenopathy, ascites and calcification did not differ significantly among the types. In the mesotheliomas, tumour attenuation (brightness on CT) was significantly higher in the portal and equilibrium phases than before contrast was given (P = 0.04 each). The authors concluded that mesothelioma tended to sit on the diaphragm and showed delayed enhancement. They called their results preliminary because there were few cases.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Retrospective case series (labelled 'case report' in the journal header, described by the authors as a preliminary retrospective study) reviewing contrast-enhanced CT scans
• Who was studied: Five dogs and seven cats with histopathologically diagnosed peritoneal tumours and no primary lesion elsewhere, scanned at the Veterinary Medical Centre of Osaka Metropolitan University and the Kinki Animal Medical Training Institute, Japan, between 2016 and 2025. There were 4 carcinomas (all cats), 5 mesotheliomas (1 cat, 4 dogs) and 3 lymphomas (1 dog, 2 cats).
• Exposure: No asbestos or other environmental exposure was studied. The article describes whole-body contrast-enhanced CT imaging features of peritoneal tumours.
• Main results:
  • Mesothelioma: lesions were in the parietal peritoneum in all 5 of 5 cases, and on the diaphragm in 4 of 5 (80%).
  • Carcinoma: lesions were in both parietal and visceral regions in 3 of 4 cases and in the visceral peritoneum in 1 of 4. Lymphoma: lesions were parietal in 2 of 3 cases and visceral in 1 of 3. Location differed significantly among tumour types (P = 0.006).
  • No significant differences among tumour types were found for tumour shape (P = 0.22) or contrast enhancement pattern (P = 0.77).
  • Ascites was seen in 5 of 5 mesothelioma cases, 2 of 4 carcinoma cases and 2 of 3 lymphoma cases. The difference was not significant (P = 0.27).
  • Lymphadenopathy was detected in only one carcinoma case (1 of 4) and in no mesothelioma or lymphoma cases.
  • Mesothelioma: median tumour attenuation was 34.7 HU before contrast, 60.7 HU in the arterial phase, 144.3 HU in the portal phase and 104.3 HU in the equilibrium phase. Attenuation was significantly higher in the portal (P = 0.04) and equilibrium (P = 0.04) phases than before contrast.
  • Carcinoma and lymphoma: attenuation showed an overall significant difference across phases, but post hoc tests did not confirm differences between specific phases.
• The authors' conclusion: The authors concluded that carcinoma was located in visceral or both parietal and visceral peritoneum, that mesothelioma tended to localise on the diaphragm and showed delayed enhancement, and that peritoneal lymphoma was not associated with lymphadenopathy. They suggested mesothelioma may be differentiated based on tumour location and attenuation value.
• Limitations the authors state:
  • Only a small number of peritoneal tumours were included, so the results should be interpreted as preliminary findings.
  • The design was retrospective, and not every lesion was examined histopathologically, so tumour classification may contain inaccuracies.
  • A fixed time-delay contrast method was used, which gives less consistent contrast enhancement than bolus tracking.
  • Dogs and cats were analysed together, and CT findings may differ between the species.
  • Mesothelioma histological types were not assessed.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma, Peritoneal mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Carcinoma, Lymphadenopathy, Ascites, Diaphragm.

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