Page 531 - Clinical Small Animal Internal Medicine

48 Gastrointestinal Imaging 499

be followed caudally into the descending colon. The might not be tolerated. Barium sulfate suspension
VetBooks.ir descending colon can also be seen caudally in the abdo­ (5%) at 7–14 mL/kg bodyweight should be slowly infused
(over 5–7 min) to allow contrast to extend to the ile­
men, dorsal to the urinary bladder. Ultrasonographic
assessment of the rectum is limited due to its location
monitor the advancement of the contrast agent within
within the pelvic canal and therefore it is not accessible ocolic junction. If available, fluoroscopy can be used to
with ultrasound. The cranial aspect of the rectum may be the colon and especially to ensure that contrast is not
visualized by tilting the ultrasound probe caudally from infused beyond the ileocolic junction. Once the con­
cranioventral to the pelvic floor. Positioning the ultra­ trast agent is infused, the catheter should be closed off
sound probe from caudal in the anus area and tilting it and the patient should be gently rolled to allow for uni­
cranially can visualize the caudal aspect of the rectum. form coating of the colon. Ventrodorsal and right lateral
Due to the typically hyperechoic content (fecal radiographic views should be obtained and additional
material and gas) in the colon, the colon wall close to the views should be added as needed to fully evaluate the
ultrasound probe may be the only aspect of the wall colon.
that is easily seen. The colon wall has a characteristic Double contrast radiography of the colon (double
ultrasound appearance and is usually hyperechoic rela­ contrast colonogram) can be performed by slowly and
tive to the small intestine. All five layers of the colon wall carefully insufflating air into the colon after a barium
are of equal thickness and are thinner than in the small enema has been performed. Double contrast colonogra­
intestine (see Figure 48.11). The colon wall in the dog phy can improve evaluation of colon wall lesions, help
and cat is usually very thin and only measures 1–2 mm identify strictures, and improve evaluation of the ileoce­
in thickness, rarely exceeding 3 mm in normal dogs. If cocolic junction.
the colon is very empty, luminal folding of the colon The mucosal surface of the colon should be smooth,
wall can be noted and the wall might subjectively appear continuous, and well defined when the colon is filled
thickened. It is a common finding that no peristalsis is with barium contrast agent. In the colon of the dog,
noted in the colon. small lymph follicles can be found and this might present
radiographically as small focal areas of thickening of the
colon wall or spicules similar to very small ulcers. These
Barium Examination of the Large Intestine
areas should become less apparent once the large intes­
Indications for performing a contrast study of the colon tine is distended. In the cat, the largest aggregate of
include evaluation of the position and appearance of the lymph follicles can be noted in the ileal area and apex of
colon, the presence of strictures, suspected intussus­ the cecum; however, this is usually not discernible on
ception, masses associated with the colon, congenital radiographs.
abnormalities, or colitis. Patient preparation should
include fasting for 24 hours if no preexisting clinical con­ Pneumocolonography
traindication is present. If only positional information of
the colon is needed, a pneumocolonography might pro­ The most common reason pneumocolonography is per­
vide sufficient information. It is important to remember formed is to gain positional information about the colon,
that an upper gastrointestinal contrast radiographic allowing differentiation between small and large intes­
study is often insufficient for evaluation of the colon tines. Pneumocolonography provides a quick, safe, and
as the colon is incompletely distended with contrast easy way to outline the entire colon but provides only
material and as fecal material often creates intraluminal limited information about involvement of the mucosa,
contrast filling defects, which can be misinterpreted as wall thickness and areas of the colon which cannot
mural or intraluminal lesions. Therefore, if a contrast be distended. In cases where a wall lesion is suspected,
study is performed to evaluate the colon wall, a more a barium enema should be performed. Pneumoco­
extensive preparation of the patient is required to ensure lonography is most easily performed by using either a
that the colon is empty. soft‐tipped catheter or catheter‐tipped syringe placed
Patient preparation should include a laxative 24 hours within the anal sphincter. In general, 1–3 mL of air/kg
prior to cleansing enemas of the colon. For the contrast bodyweight should result in sufficient filling of the colon.
radiographic procedure, sedation or anesthesia is pre­ It is important to ensure that the entire colon, including
ferred as it limits straining by the patient. Barium ene­ the cecum, is filled and distended with air. It is important
mas are best performed by placing a soft‐tipped catheter to close off the catheter or syringe once the colon is
with an inflatable cuff within the anal sphincter. The cuff insufflated to ensure that the air does not escape.
should be gently expanded to avoid overextension of the Ventrodorsal and right lateral radiographic views should
rectum or anal sphincter. In unsedated patients, expan­ be obtained and additional views should be added as
sion of the cuff or placement of a catheter into the rectum needed to fully evaluate the colon.