Date Published: April 12, 2019
Publisher: Public Library of Science
Author(s): Arcangelo Gentile, Marilena Bolcato, Gianfranco Militerno, Günter Rademacher, André Desrochers, Annamaria Grandis, Jacopo Guccione.
The term heterotopy of the spiral colon encompasses a dysmorphological condition in which the spiral loops of the ascending colon (SLACs) do not form an orderly spiraling mass adjacent to the left side of the mesojejunum. As a consequence, the spiral loops are spread over a larger surface, making them more or less movable. It has been hypothesized that the abnormal position of the spiral loops of the ascending colon might constitute a predisposing factor for an intestinal obstruction or an ileus condition. The objective of the present study was to evaluate the anatomy of the spiral loops of the ascending colon in a population of healthy calves and to determine the prevalence of dysmorphism. The investigation was carried out on 1113 slaughtered veal calves. In 472 out of the 1113 calves, the spiral loops showed conformational aspects different from what has so far been described as normal in reference textbooks. In 91 calves the condition was definitely considered a pathological deviation from normality: in fact, the spiral colon had lost its typical spiral shape with random spacing between the loops, and it was nearly or completely detached from the mesojejunum. The lack of a broad attachment of the spiral loops of the ascending colon to the mesentery could provoke an alteration of the intestinal centre of gravity, enhancing the already asymmetrical distribution of weight between the jejunum and the descending colon.
In ruminants, the large colon (Colon crassum) is composed of the ascending colon (Colon ascendens), the transverse colon (Colon transversum) and the descending colon (Colon descendens). Furthermore, the ascending colon is divided into the proximal loop (Ansa proximalis coli), the spiral loop (Ansa spiralis coli) and the distal loop (Ansa distalis coli) . The ascending colon is functionally associated with the caecum and is often associated with any caecal abnormalities. The spiral loop of the ascending colon (SLAC) is an elliptical coil on a single plane where there are 1.5–2 centripetal gyri, and the same number of centrifugal gyri with a central flexure between them [2–4]. Other than atresia coli, specific anomalies affecting the spiral loop are rare. Atresia coli is a lethal congenital disease if not treated. Affected calves are lacking parts or the entire spiral, and the distal loops of the ascending colon as well as the descending colon [5–7].
The animals selected for this study were obtained from a single slaughterhouse in November 2010; 1113 Holstein veal male calves were examined post-mortem. Their origin was unknown whereas their diet, according to the Italian regulation for veal rearing, was expected to be based on milk replacer and a small amount of fibrous food (corn silage and/or grain). Specific age was not available but their slaughter weight (body weight ranging from 240 to 275 kg) put them between 6 to 8 months of age. They were healthy and without abnormalities at pre-slaughter clinical investigation. Previous medical history was not available.
The observations regarding the SLACs of the 1113 slaughtered calves are summarised in Table 1. A normal configuration, as expected according to the veterinary anatomical literature, was observed in 641 (57.6± 2.9%) out of the 1113 calves. A conical shape looseness of the SLAC was found in 381 out of 1113 (34.2±2.8%). Partial dystopia of the SLAC was noted in 68 out of 1113 cases (6.1±1.4%) whereas complete ectopia was present in 23 out of 1113 calves (2.1±0.8%).
This study clearly indicated that the heterotopy of the SLAC represented a relatively common anatomical anomaly in young clinically healthy animals of the Holstein breed. In fact, 42.4% of the SLACs examined in this study had significant anatomical divergence from what is normally described in reference textbooks. The anomalies observed went from loose attachment of the spiral loops to the mesojejunum, abnormal elongation of the mesocolon, overlapping of adjacent loops, abnormal coiling and finally to complete detachment of the SLAC from the mesojejunum. While conical shape looseness, observed in 34.2% of the calves, might be accepted as a paraphysiological deviation from complete anatomical compliance, the same cannot be said for the animals with partial dystopia and complete ectopia (6.1% and 2.1%, respectively), that should be considered as pathological deviations. In fact, the location and configuration of the SLAC significantly diverges from the normal where the centripetal and the centrifugal loops of the SLAC should be securely attached to the left side or the medial aspect of the mesojejunum. The physiological coil-shaped disposition of the loops attached to the mesojejunum is due to the movement to which the future coils of the ascending colon are subjected during embryonic development. According to the current understanding of intestinal development, the considerable elongation of the primitive intestine at approximately the 60th day of the embryonic stage forces a part of the colon to wind itself as a flat wreath around a central bend (the future central flexure). An intestinal disk (the future SLAC) is formed with a more or less elliptical shape. Later in foetal development, this disc will superimpose itself on the left side of the mesojejunum. Thereafter, the ascending mesocolon will fuse with the mesojejunum integrating the vessels, and the fatty and the connective tissues definitely fasten the SLAC to the mesojejunum [2,10–12]. Consequently, in the physiological ontogenetically-developed animal, the SLAC is perfectly contained in the mesojejunum.
This study described four different configurations of the SLAC in a population of 6-8-month-old calves, involving loose attachment of the spiral loops to the mesojejunum, abnormal elongation of the mesocolon, overlapping of adjacent loops, abnormal coiling and finally complete detachment of the SLAC from the mesojejunum.