The histological appearance of large intestinal biopsies in dogs with clinical signs of large bowel disease.

Colonic and rectal forceps and excision biopsies of 355 dogs with clinical signs of large bowel disease were investigated. Five percent of the forceps biopsies were unsuitable for examination; all excision biopsies were of good quality. Forceps biopsies were obtained from one to eight sites, up to 60 cm cranial from the anus, while excision biopsies, mostly from tumors, were from the rectoanal region. Slight to severe colitis and/or proctitis was found in 192 dogs (54%). A single type of colitis was seen in 160 dogs; in 53 cases the lesions were local, in 107 cases multiple. A combination of different types of colitis was found in 32 dogs. Atrophic colitis, diffuse colitis and canine histiocytic ulcerative colitis were the most prominent findings, followed by ulcerative, superficial and eosinophilic colitis. Follicular, hypertrophic and aspecific granulomatous colitis were found in only a few cases. Tumors were diagnosed in 57 dogs (16%). Of these tumors 50 were of epithelial and seven were of mesenchymal origin. A high percentage (61%) of the epithelial tumors consisted of adenomas of the rectoanal region. In ten other dogs (3%) a differential diagnosis of lymphosarcoma or colitis had to be made. Colitis and colorectal tumors were more prevalent in Boxers, German Shepherds, Poodles, Great Danes and Spaniels. In the Boxers simple chronic colitis, as well as canine histiocytic ulcerative colitis were more frequently found, the latter especially in females. Other biopsy findings were edema, crypt cysts, hemorrhages, an increased number of intraepithelial lymphocytes and an increased or decreased number of goblet cells.