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Retroperitoneal paragangliomas are rare tumors of the neuroendocrine system. Only a few canine case reports are available with rare descriptions of their imaging features. The objectives of this multi-center, retrospective case series study were to describe the diagnostic imaging features of confirmed retroperitoneal paragangliomas and specify their location. Medical records and imaging studies of 10 affected dogs with cytological or histopathologic results concordant with retroperitoneal paragangliomas were evaluated. Dogs had a median age of 9 years. Four of them had clinical signs and laboratory reports compatible with excessive production of catecholamines. Six ultrasound, four CT, four radiographic, and one MRI studies were included. The paragangliomas did not have a specific location along the aorta. They were of various sizes (median 33mm, range: 9–85mm of length). Masses had heterogeneous parenchyma in six of 10 dogs, regardless of the imaging modality. Strong contrast enhancement was found in all CT studies. Encircling of at least one vessel was detected in six of 10 masses, clear invasion of a vessel was identified in one of 10 masses. In five of 10 cases, the masses were initially misconstrued as lymph nodes by the on-site radiologist. Retroperitoneal paragangliomas appear along the abdominal aorta, often presenting heterogeneous parenchyma, possibly affecting the local vasculature, and displaying strong contrast enhancement on CT. Clinical signs can be secondary to mass effects or excessive catecholamine production. Underdiagnosis and misdiagnosis of this tumor are suspected as they can be silent, of small size, or confused with other structures.

International audience; Myxoma virus (MYXV), a member of the Poxviridae family, is the agent responsible for myxomatosis, a fatal disease in the European rabbit (Oryctolagus cuniculus). MYXV has a linear double-stranded DNA genome that encodes several factors important for evasion from the host immune system. Among them, four ankyrin (ANK) repeat proteins were identified: M148R, M149R, M150R and M-T5. To date, only M150R and M-T5 were studied and characterized as critical virulence factors. This article presents the first characterization of M148R and M149R. Green Fluorescent Protein (GFP) fusions allowed us to localize them in a viral context. Whereas M149R is only cytoplasmic, interestingly, M148R is in part located in the nucleolus, a unique feature for an ANK repeat poxviral protein. In order to evaluate their implication in viral pathogenicity, targeted M148R, M149R, or both deletions were constructed in the wild type T1 strain of myxoma virus. In vitro infection of rabbit and primate cultured cells as well as primary rabbit cells allowed us to conclude that M148R and M149R are not likely to be implicated in cell tropism or host range functions. However, in vivo experiments revealed that they are virulence factors since after infection of European rabbits with mutant viruses, a delay in the onset of clinical signs, an increase of survival time and a dramatic decrease in mortality rate were observed. Moreover, histological analysis suggests that M148R plays a role in the subversion of host inflammatory response by MYXV.