A gross and microscopical morphometric evaluation of feline large intestinal anatomy

The objective of this study was to examine measurable parameters that could be used to describe the gross and microscopical anatomy of the feline colon, which has not been previously characterized. Post-mortem data were collected from 35 specific pathogen-free cats. Gross morphometric data (total colonic length, wet weight, number of lymphoid aggregates) were collected together with microscopical measurement of crypt depth and numbers, intra-epithelial lymphocyte numbers and the number of proliferating cell nuclear antigen (PCNA)-positive cells and their relative position within the crypt. Colonic length as a percentage of intestinal length was remarkably constant (20.9+/-2.0%). Crypt depth, however, showed considerable inter-cat variation (149-688 microm); the crypts became deeper with distance from the anus. Cellular proliferation was predominantly in the lower part of the crypt, and the numbers of PCNA-positive cells increased with distance from the anus. The number of lymphoid aggregates varied with distance from the anorectum and appeared to reflect the bacterial load. Intra-epithelial lymphocytes were relatively sparse (3.9+/-2.7/100 epithelial cells); they showed considerable inter-cat variation but did not vary with distance from the anus. These data suggest that to improve the interpretation of morphometric parameters by reducing inter-cat variation, samples should be taken at a consistent distance from the anus, broad reference ranges having now been established.