Unveiling the Invisible: A Case of Canine Diffuse Microscopic Pancreatic Adenocarcinoma With Normal Imaging and Gross Appearance of the Pancreas Complicated by Sterile Peritonitis and Disseminated Intravascular Coagulation.

Pancreatic adenocarcinoma is an uncommon neoplasm in dogs, typically presenting as a discrete mass with metastasis frequently identified at the time of diagnosis. Herein, we describe an unusual presentation of canine pancreatic adenocarcinoma, characterised by diffuse microscopic infiltration of the pancreas without gross abnormalities on advanced imaging or exploratory laparotomy. An 11-year-old male neutered Shetland Sheepdog presented with recurrent anorexia, lethargy, and haematuria. Diagnostic investigations revealed progressive anaemia, thrombocytopenia, pulmonary consolidations and sterile peritonitis. Despite the absence of macroscopic pancreatic abnormalities, histopathology confirmed the presence of a diffuse pancreatic adenocarcinoma with associated fibrinohaemorrhagic peritonitis and disseminated intravascular coagulation. There was no evidence of gross metastasis. This rare presentation highlights the diagnostic challenges posed by microscopic pancreatic neoplasia and emphasises the necessity of early histopathological evaluation in cases of unexplained systemic inflammation. This case also underscores the importance of considering paraneoplastic syndromes and systemic complications in the context of pancreatic cancer, even in the absence of detectable metastases.