Abstract
Atresia or stenosis of the intestinal tract is uncommon in mammalian species and rarely reported in avian species.1 Atresia is the complete occlusion of the lumen, and stenosis implies incomplete occlusion. Atresia is further classified as membrane atresia, in which the obstruction is formed by a simple membrane; cord atresia where the blind ends of the intestine are joined by a cord of connective tissues; and blind end atresia that has a completely missing segment of intestine and possibly the mesentery. Segmental ischemia from a mechanical lesion of the blood supply (ischemia) such as from a volvulus, intussusception, or malrotation is purported to be the primary cause.1,2 This etiology has been supported by experiments done in lambs, dogs, rabbits, and chickens where a persistent occlusion of the blood supply of a fetal intestine results in atresia.3 In domestic mammals, atresia is most commonly described in equine, bovine, and porcine species. In some of these cases, there is a suggestion of a heritable condition, as atresia can be identified back along common breeding lines.2
With the exception of the experimentally induced lesions of chickens, no other reports are found of intestinal atresia of avian species.3 One, and possibly two, breeding pairs of helmeted guineafowl (Numida meleagris) produced several clutches of chicks that have died shortly after hatching. These chicks, three of which were examined, had segmental intestinal atresia at various levels. One had a focal colonic atresia at the level of the cloaca. There was no connection between the end of the large intestine to the cloaca. The intestinal section was greatly dilated. In this chick, the large intestinal atresia resulted in extensive damage to the kidney, most likely due to the enlarging mass of the intestine. A second guineafowl had the lesion within the cloaca, where the closure was within the cloaca close to the level of the vent (coprodeum). The large intestinal blind end into the cloaca was lined with mucosal epithelium and submucosal tissue. There is no opening or connection through the vent. The cloaca had developed and a bursa of Fabricius was recognized. Again, the intestinal sections were greatly dilated with intraluminal amorphous material. A third guineafowl chick had a lesion most suggestive of cord atresia, with a connection from the cloaca to the vent by a thin remnant of muscular tunic connecting the coprodeum and the proctodeum. In this chick, there was also no connection between the ventriculus and small intestine. On this third chick, there was also an apparent cardiac lesion in that the cardia atria were bilaterally dilated. No specific lesions were noted of the heart, with the exception of the atrial dilation. No further cases have been identified in the next breeding season.
Literature Cited
1. van der Gaag, I., D. Tibboel. 1980. Intestinal atresia and stenosis in animals: a report of 34 cases. Vet Pathol. 17(5):565–574.
2. Smith, D.F., N.G. Ducharme, S.L. Fubini, W.J. Donawick, and H.N. Erb. 1991. Clinical management and surgical repair of atresia coli in calves: 66 cases (1977–1988). J Am Vet Med Assoc. 199(9):1185–1190.
3. Tibboel, D., C.J. van Nie, and J.C. Molenaar. 1980. The effects of temporary general hypoxia and local ischemia on the development of the intestines: an experimental study. J. Pediatr. Surg. 15(1):57–62.