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 until 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 reduce 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.
Indications for cystography include chronic unresponsive hematuria, non-visualization of the bladder post trauma, suspect radiolucent calculi, and post bladder or urethral surgical evaluation. There are three different types of cystograms: positive, negative, and double contrast. A positive contrast cystogram is indicated to assess for bladder rupture and urachal diverticulum. A negative contrast procedure is indicated to assess the ureterovesicular junction for ectopic ureters. A double contrast cystogram should be performed to diagnose cystitis, non-radiopaque cystic calculi, mucosal abnormalities and bladder wall neoplasia. To perform a cystogram, initially you need to obtain survey radiographs to make sure there is no overlying feces. A preplaced urethral catheter is necessary. Dilute high osmolar contrast media is utilized for a positive contrast cystogram. Dilute 1 part contrast to 2 parts sterile saline. The maximum dose is 5ml/ lb, but only use enough until the bladder palpates tight. Lateral and 45" VD oblique views are obtained. A negative contrast cystogram utilizing room air is easiest. However carbon dioxide and nitrous oxide are more soluble in blood, thus are safer and have lower incidence of fatal air embolism compared to room air. The maximum dose is again 5ml/ lb. 45' VD obliques help to visualize the ureterovesicular junction. For a double contrast cystogram, initially administer non diluted high osmolar iodine through the urethral catheter at a dose of 1ml/ lb. Next administer room air, CO2, or N20 at a dose of 5ml/ lb (until the bladder feels taught). VD, right and left lateral recumbent, and VD oblique views are obtained. A normal cystogram shows a less than 2mm thick bladder wall. Ureterovesicular reflux can be normal in dogs less than 6 months of age and should not be viewed as pathologic. Mucosal abnormalities occur with cystitis and irregularity is detected which is usually more severe in ventral apex. This is accentuated with inadequate bladder distention. Intramural thickening is often caused by neoplasia, commonly transitional cell carcinoma. However inflammation and hemorrhage are also possible differentials. Filling defects in the contrast can be air bubbles, calculi, or blood clots. The location of the filling defects helps to determine their composition. Air bubbles are located at the periphery of contrast and show smooth margins. Calculi by comparison are located in center of contrast and have irregular margins. Blood clots are located anywhere in bladder and are irregular in shape and margination. Contrast can be located outside of bladder but within urinary tract in cases of urachal anomalies and bladder diverticuli. Contrast which is uncontained is seen within peritoneal cavity and is due to bladder rupture. The urinary tract can communicate with other hollow visceral structures when rectal or vaginal fistulas are present.
Urethrography is indicated when there is dysuria, pelvic fractures, voiding hematuria with normal cystography or to localize and characterize urethral rupture. Initially survey radiographs are obtained. With male dogs a "butt shot" with the rear legs pulled forward centered on the membraneous urethra is necessary. General anesthesia is needed and a Foley catheter is inserted into very distal urethra. Pre-fill the catheter with contrast so that air bubbles won't interfere with study. 2 to 5 mls of 2% lidocaine is infused into the urethra to prevent urethral spasm. Utilize dilute iodine (1 part contrast to 2 parts sterile saline). Male dogs require more contrast (between 10 to 20mls), where as female dogs and cat use only 5-10 mls. If you are unable to place a urethral catheter, you can do an antegrade (normograde) urethrogram by performing an excretory urogram and then placing pressure on bladder and radiographing during voiding. For female dogs and cats this is the only way to see entire urethra. Normal dog prostatic urethra is the widest whereas the membraneous urethra is narrowest. In cats the penile urethra is narrowest. Filling defects in the urethra can be air, calculi, or blood clots. Their effect on the urethral wall allows determination of composition. Air is round to oval with smooth margins and defined borders. Calculi are variable in shape with irregular margins and ill-defined borders. Calculi can cause widening of urethral lumen. Blood clots are variable in shape with irregular margins and ill-defined borders. Neoplasia such as transitional cell carcinoma and granulomatous urethritis can resulting in regional luminal narrowing with irregular mucosal margins. Extraluminal obstruction is caused by prostatic masses. Urethral trauma can be iatrogenic or due to pelvic fractures and you will note extravasion of contrast material on the urethrogram.