Rare intestinal malformation (diverticulum confluens) in a horse.

Intestinal congenital diverticula are uncommon in domestic animals (Barker et al. 1993). They can arise from the omphalomesenteric (vitelline) duct or from each part of the intestine. Rarely, the vitelline duct may be retained in postnatal life as a patent duct extending from the antimesenteric side of the intestine to the umbilicus (fistula omphalo-enterica completa). In some cases, only the portion adjacent to the abdominal wall remains patent forming an umbilical pouch (fistula omphaloenterica incompleta externa). More commonly, only the portion immediately adjacent to the intestine remains patent (Meckel’s diverticulum or fistula omphalo-enterica incompleta interna). The vitelline duct can be obliterated at both its ends and present one or more cysts along the corresponding tract. In horses, only the fistula completa and Meckel’s diverticulum have been described (Godlück 1967). Meckel’s diverticulum is present as a short cone-shaped sac of up to 10 cm diameter, which may be attached by mesodiverticular folds to the ventral abdominal wall. Hahn (1877) described a large gastro-like Meckel’s diverticulum with capacity of about 7 litres. Other congenital diverticula not arising from the vitelline duct occur rarely in horses as well as in other animal species (Godlück 1967). A classification of the latter is generically based on their shape: sac-like, double, loop, confluence and spindle diverticula. Few cases are described in the veterinary literature. Joest (1910) observed a double diverticulum in the small colon of a horse: from an intestinal loop, 2 sac-like symmetric and opposing dilatations emerg e d , each of them of a baby’s head size, both with normal intestinal wall structure. Schmidt (1940) observed different types of intestinal dilatations in horses, one of them corresponding to a congenital rectal diverticulum. It derived from the ventral flexure of an abnormal colon-rectal loop and was directed (and closed) dorsocaudally. Confluence diverticula are very rare intestinal dilatations which have been described only in swine. In a case observed by Joest (1905) the diverticulum was formed by 2 neighbour colon loops and 6 small intestinal loops. The case described by A s e r (1918) occurred in a 10-week-old swine, where different small intestine loops merged in a fist-sized dilatation. In 2 further cases, Kitt (1923) found dilated, stomach-like sacs, resulting from the confluence of 3 small intestinal loops and consequently endowed with 6 openings. The present study derives from the observation of a confluence diverticulum in a horse.