Predominance of hypoechoic tissue changes in nine dogs with malignant prostatic lymphoma.

Neoplasia of the prostate is relatively uncommon in dogs with adenocarcinoma being the most common type. Non-epithelial tumors are rare and only individual cases of malignant lymphoma affecting the prostate have been reported. The purpose of this multi-institutional, retrospective, descriptive study was to characterize the ultrasonographic features of canine prostatic lymphoma. Inclusion criteria were an abdominal ultrasound and cytological/histological diagnosis of malignant prostatic lymphoma. Ultrasonographic features were recorded based on the original ultrasonographic reports and consensus opinion of two readers on the available image sets retrospectively. Nine dogs met the inclusion criteria with a mean age of 6.5 years. Seven dogs were intact and two neutered. Subjective prostatomegaly was noted in all patients however not reproducible by objective measurements. Altered shape with rounded/irregular margins was detected in 78% of the cases. All prostates presented either diffuse (three dogs) or focal/periurethral (four dogs) and/or multifocal areas of hypoechogenicity (three dogs). In one dog, focal and multifocal hypoechoic changes co-occurred. Prostatic mineralization was not present in any of the cases. Ultrasonographic features of infiltrative disease of multiple organs and/or lymphadenopathy was found in all cases. Even though malignant lymphoma is rare in the prostate, it should be included in the list of differentials in patients with hypoechoic lesions/areas, altered shape, lack of mineralization of the prostatic parenchyma and evidence of multiorgan involvement.