Computed tomographic staging of dogs with anal sac adenocarcinoma

Objectives To describe the CT appearance of anal sac adenocarcinoma lesions in a population of dogs including the relations between primary tumour, and locoregional and distant metastasis. Materials and Methods Retrospective review of dogs with confirmed anal sac adenocarcinoma and available CT images of the thorax, abdomen and pelvis. Results A population of 70 dogs were included in the study. No association was found between anal sac mass size and presence or absence of iliosacral lymph node enlargement. The prevalence of local metastatic disease characterised by iliosacral lymphadenomegaly in this study was 71%, with pulmonary metastases identified in 11% of cases. There were no cases of distant pulmonary metastasis without concurrent locoregional lymphadenomegaly. Clinical Significance In our population of dogs local metastatic spread of anal sac adenocarcinoma was common, with a relatively low prevalence of pulmonary metastasis. The study demonstrates the importance of thorough rectal examination and/or imaging to assess the iliosacral lymph centre in this disease irrespective of the size of the anal sac mass.