Fun with radiographic contrast procedures (Proceedings)
Indications for an esophagram include regurgitation, gagging or retching, dysphagia, cough associated with eating, as well as the presence of a mediastinal, cervical, or thoracic mass. The pertinent anatomy to remember is that in the cat the caudal 1/3 of the esophagus is smooth muscle. The contrast media utilized includes paste which adheres to the mucosal surface (allowing for best mucosal evaluation), barium suspension mixed with food (which better outlines space-occupying lesion or stenoses in the esophagus), and organic iodides which are only used if perforation is suspected, but are not recommended for routine use due to poor mucosal coating. If you are going to use an iodine contrast media, nonionic agents (ie Omnipaque), which are isomolar are recommended. Hyperosmolar agents if aspirated cause fulminant pulmonary edema. If you must sedate an animal to perform the procedure, you can use low dose acepromazine. Initially, you administer barium paste into the mouth and wait for the patient to swallow, take lateral radiographs of the thorax and repeat paste administration until able to visualize coating of the entire esophageal mucosa. Next you feed barium mixed with wet food and wait for swallowing. Take radiographs until all the esophagus is seen. If no abnormalities are identified up to this point, feed barium soaked kibble and take radiographs unitl all the esophagus is seen. Normal esophagrams in cats should show herringbone striations in the caudal 1/3 of esophagus. In normal dogs there are 6-12 smooth, linear longitudinal folds along length of esophagus. In brachycephalic breeds and Shar Pei's slight ventral deviation and redundancy of the esophagus at thoracic inlet can be detected and is not considered abnormal. Abnormal esophagrams reveal diffuse or focal luminal dilation, focal or diffuse luminal narrowing, luminal filling defects, or displacement from the normal anatomic location. Luminal dilation can be generalized due to megaesophagus or locally dilated proximal to an obstruction (caused by an intraluminal foreign body or extraluminal stricture due to vascular ring anomaly). Focal or diffuse luminal narrowing can occur from esophagitis. With esophagitis you also see an irregular mucosal pattern which is spiculated. Luminal filling defects are most often due to foreign bodies though they can also be due to neoplasia.
Upper GIIndications for an upper GI exam include persistent vomiting, suspected (but unconfirmed) obstruction/ FB, abdominal mass (very often for birds), and suspected perforation of stomach or intestines. Upper GI exams are contraindicated if there has been administration of drugs that slow gastrointestinal transit such as xylazine or atropine as well as perforation or mechanical obstruction which is confirmed on plain films. The contrast media which should be used is micropulverised barium suspension. It comes as a 60% solution and you should dilute with 1 part barium to 1 part water to make it a 30% solution. THE DOSE IS 6ML/ LB ADMINISTERED VIA OROGASTRIC TUBE. The dose is only reduced to 4ml/lb for giant breeds! If you administer orally, you will not be able to give enough volume fast enough to fully distend the stomach. BIPS and iodinated contrast produce inferior studies and are not recommended. Prior to performing an upper GI exam, survey radiographs should be obtained. (Sometimes the diagnosis is obvious and doesn't require barium!). If the colon contains feces, an enema should be administered to remove colonic contents. Acepromazine in dogs and Ketamine with Valium in cats can be used if sedation is necessary to administer a fractious patient. Four radiographs (DV, VD, right lateral and left lateral) centered on the stomach are taken immediately after barium administration. Then VD and right lateral views of the abdomen are obtained at 15 minutes, 30 minutes, 60 minutes, and then every hour until the contrast reaches the colon.
Normal upper GI exams show a continuous rope-like column of barium. In dogs, "pseudoulcers" are seen in the duodenum on the antimesenteric border, which actually represent Peyers Patches and the normal small intestinal diameter is approximately 1.6x height of L5 at narrowest point. The duodenum is slightly wider than the jejunum. In dogs, barium is in the duodenum by 15 minutes, the jejunum by 30 minutes, the ileocolic junction by 120 minutes and only in the colon between 3-5 hours. In cats, there is usually minimal or no luminal gas identified on survey films. The normal diameter of small bowel (serosal to serosal surface) is 10-12mm. A "string of pearls" is often visualized in the feline duodenum due to peristalsis. Barium transit time through the small intestines is slightly faster in the cat than the dog, being present in the duodenum by 10 minutes, the jejunum by 20 minutes, at the ileocolic junction by 60 minutes and completely in the colon in 2-3 hours. Mechanical obstruction can be confirmed on an upper GI exam. Physiologically with mechanical obstruction the bowel initially is hyperperistaltic proximal to the obstruction but then becomes fatigued, hypotonic and dilates. Radiographic signs of mechanical obstruction include severe focal/ segmental dilation of the small bowel which results in two populations of bowel with hairpin turns, squared off dilated loops that appear to "stack". Functional ileus is the failure of passage due to generalized neurologic or muscular dysfunction of the intestinal wall. Radiographically with function ileus there is less dilation than with mechanical ileus and all the small bowel is distended similarly. Overall there is slowed gastrointestinal transit. Enteriitis results in rapid gastrointestinal transit time, spiculation of mucosal margins, and decreased luminal width. Linear foreign bodies result in plication of the bowel with most of small bowel located in right cranial abdominal quadrant. Intussception causes a mass effect on survey radiographs and can appear as a coilspring with barium surrounding a filling defect.