Colonoscopy in the Dog and Cat
Albert E. Jergens, DVM, MS, Diplomate ACVIM
Iowa State University
Ames, Iowa, USA
In recent years, the availability and extended use of rigid and flexible endoscopy has led to a marked increase in diagnostic procedures involving visualization and biopsy of the upper and lower gastrointestinal (GI) tract in domestic animals. Endoscopy provides rapid, minimally invasive examination of mucosal surfaces and permits procurement of tissues for histologic and cytologic examination, or of fluid specimens for laboratory evaluation. Key to the success of GI endoscopy in detecting mucosal disease is proper biopsy technique. Pertinent considerations include 1) the organ being sampled, 2) nature of the suspected lesion, 3) presence of focal versus diffuse mucosal disease, 4) selection of biopsy instrumentation, and 5) post-biopsy specimen handling considerations.
ABNORMAL MUCOSAL APPEARANCES
Gross mucosal abnormalities are common and range from the obvious, such as intraluminal masses, to discrete erosions. Mass lesions are usually seen with infiltrative mucosal diseases (malignant neoplasia, benign polyps, inflammatory disorders) and may be pedunculated or sessile. Masses should be biopsied deeply to avoid necrotic surface debris and superficial cells which may obscure a correct diagnosis. If diffuse neoplasia is suspected, multiple biopsy specimens deep within the lamina propria should be obtained from both normal and abnormal appearing mucosa.
Consistent endoscopic terminology has been proposed to aid in lesion description and the formulation of a definitive diagnosis. Erythema denotes mucosal redness which may be pathologic or a normal physiologic response to endoscope induced trauma, blood flow changes associated with anesthesia, or warm water enemas. Friability describes the ease with which the mucosa is damaged by contact with the endoscope or biopsy instrument. Alterations in mucosal texture are described as increased granularity. Granularity of the intestinal mucosa may be influenced by gland height and crypt depth as the light of the endoscope reflects off these structures.
Mucosal ulceration-erosion is defined as an endoscopically visible breach in mucosal integrity associated with active hemorrhage. Ulcers are typically focal, crateriform, well-circumscribed lesions which extend deeply into the adjacent mucosa and contain central fibrinous exudate. Erosions are discrete, superficial mucosal defects which do not have raised margins or necrotic centers. Ulcers and erosions are characteristic of inflammatory and neoplastic lesions. Erosive lesions are biopsied directly. Ulcerative lesions are best biopsied by obtaining specimens from the ulcer rim as it interfaces with adjacent tissue. Mucosal biopsies from tissue surrounding an ulcer should also be obtained to characterize benign from malignant ulcer disease.
NORMAL MUCOSAL APPEARANCE
Normal colonic mucosa is pale pink, smooth, and glistening. Submucosal blood vessels are readily observed with adequate insufflation. Lymphoid aggregates, 3-5 mm in diameter and umbilicated, are diffusely abundant in the aboral colon. Visual inspection of the cecum and ileocolic valve should be performed in all patients undergoing full colonoscopy. Parasitism, cecal inversion, ileocolic intussusception, inflammatory bowel disease, and neoplasia may cause mucosal lesions in this region.
ENDOSCOPIC EXAMINATION OF THE LARGE INTESTINE (COLONOSCOPY)
Indications: Clinical signs of chronic colonic disease including large bowel diarrhea (exhibited by tenesmus, dyschezia, hematochezia, or the passage of mucoid feces). Colonoscopy is particularly useful in the diagnosis of IBD (lymphocytic-plasmacytic colitis) in both dogs and cats.
Patient preparation. Withhold food for 18-24 hours. In dogs, I prefer to administer two doses of a colonic electrolyte lavage solution (GoLYTELY, 20 ml/kg/dose given 4-6 hours apart orally) the afternoon before an AM endoscopy. The morning of the procedure, I give a warm-water enema to both dogs and cats.
Instrumentation. A rigid endoscope is sufficient for examination of the descending colon alone. Since many inflammatory disorders diffusely affect the colon, visualization and biopsy of the descending colon are often diagnostic. Flexible endoscopy allows for visualization of all colonic regions as well as retrograde ileoscopy. Biopsy instrumentation should include serrated jaw pinch biopsy instruments.
Abnormal findings. Similar as for enteroscopy including increased mucosal granularity, increased friability, and the presence of ulcer/erosions. Loss of submucosal vascularity is a significant finding and may be caused by mucosal edema, the accumulation of exudate (blood, mucous, necrotic debris), or infiltration of inflammatory or neoplastic cells. Masses and colonic nematodes (Trichuris vulpis) are less common endoscopic observations.
Biopsy recommendations. Colonic biopsies are always obtained regardless of mucosal appearance. Flexible endoscopy is preferable since examination and biopsy of the transverse and ascending colons may also be performed. Focal lesions are biopsied directly. In the absence of gross mucosal abnormalities, obtain 3-4 biopsy specimens from each colonic region using serrated jaw pinch biopsy forceps.
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Albert E. Jergens, DVM, MS, Diplomate ACVIM