Presumed atypical cor triatriatum dexter in a geriatric dog: A case report.

Membranous structures within the right atrium (RA), such as the Chiari network, eustachian valve, Thebesian valve, and cor triatriatum dexter (CTD), can present with overlapping imaging features and complicated diagnoses. A 17-year-old male Maltese presented with a cardiac murmur, cough, anorexia, and exercise intolerance. Echocardiography revealed a mobile membrane in the RA, dividing it into two chambers. Computed tomography (CT) confirmed this finding, demonstrating differential attenuation of contrast between the chambers. The vascular connections and anatomical relationships of the structure differed from those of previously reported CTD types. Although other sinus venosus valve remnants were considered, the findings supported a provisional diagnosis of atypical CTD. This case highlights the utility of multimodal imaging for the characterisation of right atrial membranous structures. In human medicine, a detailed anatomical comparison of sinus venosus valve remnants aids in the differential diagnosis. Applying a similar approach in veterinary medicine, especially in geriatric patients, may improve diagnostic accuracy. Comprehensive imaging evaluations, including echocardiography and CT, are recommended to assess RA membranes that may be misinterpreted as variants of the CTD or other embryological remnants.