Comparison of Barium and Iohexol as Gastrointestinal Contrast Media in Avian Radiography
Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA;
Barium sulfate, iohexol, and half-strength iohexol solutions were compared as gastrointestinal contrast media in three different psittacine species. Gastrointestinal contrast studies utilizing iohexol were of comparable diagnostic quality to those using the more routinely recommended barium sulfate. Iohexol should be considered as an equivalent alternative when planning avian gastrointestinal contrast studies. Half-strength iohexol did not provide adequate opacification as a gastrointestinal contrast agent. Although not isotonic, no adverse effects were associated with the use of iohexol as a gastrointestinal contrast agent. In all three species, films made within the first hour of administration of contrast media will show all portions of the gastrointestinal tract opacified, with the exception of the cloaca.
The indications for gastrointestinal contrast radiography in avian medicine are generally the same as in mammals. Studies to assess different contrast media in birds are limited.2,5 The primary indications for a gastrointestinal contrast study in birds include regurgitation, vomiting or diarrhea, palpation of an abnormal crop or abdominal mass, or abnormal radiographic findings such as an obstructive bowel pattern, organomegaly or organ displacement.4 Similar to mammals, barium sulfate suspension is contraindicated if gastrointestinal perforation is suspect.7 However, the routine use of iodinated gastrointestinal contrast agents have not been recommended for GI studies in birds,6 probably because of the hypertonicity of the solutions.
The use of a non-ionic, iodinated contrast media, iohexol (Omnipaque, Winthrop Pharmaceuticals, New York, NY, USA), as a gastrointestinal contrast agent was reported in a cockatiel (Nymphicus hollandicus) with crop stasis.9 Iohexol (240 mgI/ml) has low osmolality (520 mOsm). A recent study in pigeons (Columba livia) described the safety and efficacy of iohexol.3
The purpose of this study was to evaluate gastrointestinal studies made with either barium sulfate suspension or iohexol solution in three psittacine species of differing body size.
Materials and Methods
Nine birds were used in a cross-over design study, each bird serving as its own control. We used three African grey parrots (Psittacus erithacus), body wt range 371–440 g; three monk parakeets (Myiopsitta monachis), body wt range 104–148 g; and three budgerigars (Melopsittacus undulatus), body wt range 43–47 g. On three separate occasions, each bird underwent a complete gastrointestinal radiographic study. Contrast media used was barium sulfate 25% w/vol suspension, iohexol 240 mgI/ml solution, and iohexol 120 mgI/ml solution (normal saline diluent). The volume of contrast media administered was the same for each study, but the smaller species were given relatively more contrast media. The African grey parrots received 0.025 ml/g body wt (approximately 10 ml), and the monk parakeets and budgerigars received 0.05 ml/g body wt (approximately 6 ml and 2 ml, respectively).8 Birds were fasted overnight preceding the study. All birds were dosed using a flexible feeding tube to deposit the contrast media into the crop. Radiographs were made with the bird physically restrained on a plexiglass restraint board; neither sedation nor anesthesia was used to avoid chemical effects on gastrointestinal motility.6 Radiographs were made from the right lateral recumbent and ventrodorsal positions at 5, 15, 30, 60, 120, 180 and 240 min after contrast media administration. All radiographs were made on Lanex Fine screens (Kodak X-Omatic Cassette, Kodak, Rochester, NY, USA) with TML -RA film (Kodak, Rochester, NY, USA) exposed with a 40" SFD at 2.5 mAs and either 52 kvp (budgerigars) or 54 kvp (parrots). The birds were observed closely during and for 48 hr following the procedures. This protocol was approved by the Cornell University Institutional Animal Care and Use Committee.
Each study was evaluated individually and separately by two radiologists (NLD, VTR). While the species was obvious, the contrast medium was not known during the reading. Each examiner was asked to comment on intestinal transit, clarity of viscera and ability to identify specific regions in the gastrointestinal tract. Evaluations were considered qualitative; no statistical analyses were made. There was good agreement among the two radiologist examiners and results are presented as consensus.
In African grey parrots, the undiluted iohexol opacified the proximal portions of the gastrointestinal tract longer than either dilute iohexol or barium, although this was not true in every case. The diluted iohexol study was less opaque overall and had faster transit times through the bowel. Lumen margins were harder to see and opacity tended to decrease with time. Some luminal contents appeared frothy with indistinct margins.
In monk parakeets all contrast agents tended to leave the upper gastrointestinal tract more rapidly. The intestines remained opacified for several hours with any contrast agent. Overall transit times were rapid with either iohexol concentration. For the diluted iohexol, readers felt there was more rapid GI transit and poor opacification of structures.
In the budgerigars the iodinated contrast agents tended to stay in the crop and esophagus though emptied faster from the proventriculus and venticulus. As in other species studied, films made within the first hour will show all portions of the gastrointestinal tract except the cloaca.
None of the birds regurgitated contrast media after administration. However, some birds did reflux some contrast (any type) later in the study. This was documented by appearance of contrast media in the nasal sinus cavity. This usually occurred after 2 hr. No clinical abnormalities were associated with this phenomenon or in general during the 48-hr observation period following each study.
In general, diluted iohexol, not surprisingly, produced the least opacification of bowel. Some studies showed decreasing opacity with time most likely as a result of further dilution. Barium produced consistently well opacified bowel lumens in all the study species. Iohexol-240 mgI/ml also produced well opacified bowel lumen and was not distinguished from barium by the observers of this study.
Discussion and Conclusions
Gastrointestinal contrast studies are performed to enhance visualization of the morphology of the intestinal tract. Alteration in the size, shape, opacity, location and distribution of the components of the bowel are interpreted to various disease conditions. Contrast materials make it easier to see the bowel and discern these changes. Functional aberrations of transit time, partial or complete obstruction, or malabsorption and maldigestion are interpreted from changes in morphology of the bowel. Morphologic abnormalities are easier to describe and functional conclusions are subject to interpretation error. This study confirms that different contrast materials are suitable to visualize the gastrointestinal tract in avian species and there is variation between species, among individuals, and between contrast media in the ability to demonstrate bowel morphology.
Results suggest that either 25% w/v barium suspension or iohexol-240 mgI/ml are useful for avian GI radiography. Diluted iohexol produced less opaque bowel and increased rate of transit through the proximal portions of the intestine making evaluation of these regions more difficult. Also, dilute contrast makes lumen margins less distinct and defeats the major purpose of contrast radiography. These results contrast with those of a recent study that concluded that half and full strength iohexol were equally efficacious in such studies.1
Both barium and full strength iohexol provide excellent morphologic distinction and choice of agent is mediated by consideration of possible bowel perforation. When suspected, the non-ionic, iodinated contrast medium, iohexol is preferred over the particulate barium suspension. While not confirmed, we strongly suspect that barium in the coelomic cavity would induce an inflammatory response as it does in mammals. Though not isosmotic at the undiluted concentration, there were no ill effects observed with iohexol in any of the birds.
All contrast media moved rapidly into the intestines in all birds. In most studies, the intestine was opaque very early and stayed so for nearly 4 hr. From these results, a contrast study of the avian gastrointestinal tract can be performed in 1 hr in most birds. Films should be made immediately after contrast is given and subsequent examinations timed by the rate of transit through the bowel. If the “upper GI” regions are of prime interest, more films should be made early in the hour. We could recommend every 15 min, though this may be very stressful for ill birds. We do recommend that sufficient films be made to visualize all portions of the gastrointestinal tract and that any morphologic abnormalities are persistent in more than one film. This prevents transitory phenomenon such as incomplete lumen filling, peristalsis, or ingesta being confused with pathologic processes. A true morphologic abnormality should be persistent on multiple films.
This study suggests that either iohexol 240 mgI/ml or 25% w/v barium suspension can be used for safe, effective, and efficient contrast studies of the avian gastrointestinal system.
This study was supported by a grant from the Joint Alumni/Faculty Committee on Unrestricted Funds of the Cornell University College of Veterinary Medicine.
1. Ernst S, J.M. Goggin, D.S. Biller, et al. 1998. Comparison of iohexol and barium sulfate as gastrointestinal contrast media in mid-sized psittacine birds. J Avian Med Surg 12:16–20.
2. Krautwald, M.E.. 1987. Radiographic examination of the urinary tract in birds with organic iodinated contrast media. Proc Assoc Avian Vet 177–193.
3. Love N.E., O. Ramirez, L. Degernes, et al. 1997. A comparison of iohexol and barium sulfate suspension in the radiographic evaluation of the gastrointestinal tract of the pigeon. Proc Ann Conf Am Coll Vet Radiol. Chicago: 47.
4. McMillan M.C. 1983. Avian gastrointestinal radiography. Compendium of Continuing Education for Practicing Veterinarians 5:273–284.
5. McMillan M.C. 1988. Imaging of avian urogenital disorders. J Assoc Avian Vet 2: 74–82.
6. McMillan M.C. 1994. Imaging techniques. In: Ritchie BW, Harrison GJ, Harrison LR. Avian Medicine: Principles and Applications. Lake Worth, FL: Wingers Publishing.
7. Moon M. and W. Myer. 1986. Gastrointestinal contrast radiology in small animals. Semin Vet Med Surg (Small Anim). 1:121–143.
8. Smith B.J. and S.A. Smith. 1997. Radiology. In: Altman RB, Clubb SL, Dorrestein GM, Quesenberry K. Avian Medicine and Surgery. Philadelphia: WB Saunders.
9. Williams J., D.S. Biller, and W. Myer, et al. 1993. Use of iohexol as a gastrointestinal contrast agent in three dogs, five cats, and one bird. J Am Vet Med Assoc 202:624–627.