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Rectal Mucosal Biopsy
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Rectal mucosa is easily biopsied with little risk to the horse.
Rectal Mucosal Biopsy
Indications
- Acute or chronic diarrhea. Concurrent culture of rectal mucosa and feces increases the likelihood of isolating Salmonella spp. compared to fecal culture alone. Diarrhea of some horses is associated with the infiltration of mucosa and submucosa with populations of inflammatory (i.e., infiltrative bowel disease) or neoplastic cells, and for some of these horses, lesions can be found, and diagnosis made, by histological examination of rectal mucosa.
- Weight-loss attributed to intestinal disease. Rectal biopsy may aid in the diagnosis of intestinal lymphosarcoma and some types of idiopathic infiltrative bowel disease. For some horses with granulomatous enteritis or multisystemic, eosinophilic, epitheliotropic disease, antemortem diagnosis is made by histological examination of rectal mucosa. Lymphocytic-plasmacytic enterocolitis and eosinophilic enterocolitis are unlikely to be diagnosed by histological examination of rectal mucosa.
Contraindications
- The procedure can be dangerous for the horse or the clinician taking the sample, if the horse is fractious and not easily controlled.
- Tenesmus The procedure can be dangerous for horses with acute diarrhea, because an arm in the rectum of these horses can cause them to strain, which can result in rectal injury. (Caudal epidural anesthesia may prevent straining during rectal biopsy of horses with acute diarrhea.)
Materials
- An alligator-type biopsy forceps (such as a mare endometrial biopsy forceps)
- A small gauge, hypodermic needle to remove the specimen from the forceps
- Lubrication and an obstetrical sleeve
- 10% formalin and a bacterial transport medium. Bouin’s solution is a poor choice for a fixative for rectal mucosa, because it makes eosinophils less conspicuous.
Procedure
- Restraint is the same as for safe palpation of the abdomen per rectum.
- The rectum is cleared of feces. Proctoscopic examination, using a tube vaginal speculum or a colonoscope, may aid in identifying areas of disease for biopsy.
- The closed jaws of the biopsy forceps are protected by a lubricated hand and carried into the rectum to elbow depth (Fig. 22.1).
- The jaws of the forceps are opened, and rectal mucosa from the 10 or 2 o’clock region of the rectum is grasped between the thumb and index finger and pulled into the jaws of the biopsy forceps (Fig. 22.2). The dorsal aspect of the rectum should not be biopsied to avoid trauma to the rectal vasculature.
- Mucosa can be placed directly in fixative, but by orienting the tissue on filter paper, sections can be taken at right angles to the surface for better histological evaluation.
- Mucosa for bacteriologic culture is placed in an enrichment medium or physiologic saline solution and then chilled for transport.
Figure 22.1. The closed jaws of the biopsy forceps are protected by a lubricated hand and carried into the rectum to elbow depth.
Figure 22.2. The jaws of the forceps are opened, and rectal mucosa from the 10 or 2 o’clock region of the rectum is grasped between the thumb and index finger and pulled into the jaws of the biopsy forceps.
Interpretation
- Salmonella spp. is often cultured from rectal mucosa of horses with salmonellosis, even when fecal cultures are negative for the organism.
- Rectal biopsy is often helpful for diagnosis of infiltrative bowel disease. A histopathologist interprets the biopsy, but a brief histological description of some intestinal diseases is presented.
- Sheets of macrophages or epitheliod cells and circumscribed granulomas in the mucosa or submucosa are seen during histological examination of rectal mucosa of horses with granulomatous enteritis.
- Lymphoid and plasma cells can be found in rectal tissue of horses with various intestinal diseases. Finding a lymphocytic-proctitis during histological examination of rectal tissue, particularly if lymphocytic infiltration is mild, may not justify a diagnosis of lymphocytic-plasmacytic enteritis.
- Eosinophilic enterocolitis is unlikely to be diagnosed based on results of a rectal biopsy, because eosinophilic infiltrates can be found in the rectal mucosa of normal horses. The presence of eosinophilic granulomas associated with vasculitis and fibrinoid necrosis of intramural vessels in rectal tissue is considered diagnostic of multisystemic, eosinophilic, epitheliotropic disease.
Complications
- Complications are very unlikely. Post mortem examination of horses that have had their rectal mucosa biopsied indicates that the biopsy site is healed within 3 days and is difficult or impossible to find after 5 days.
- Trauma from recent palpations per rectum can cause histological changes in the mucosa. Biopsies intended for histological examination should, therefore, be taken from the dorsolateral aspect of the rectum and before extensive palpation is performed.
Suggested Readings
Palmer JE, Whitlock RH, Benson CE, et. al. Comparison of rectal mucosal cultures and fecal cultures in detecting Salmonella infection in horses and cattle. Am J Vet Res 46:697-698, 1985. - PubMed -
Lindberg R, Nygren A, Persson SGB. Rectal biopsy diagnosis in horses with clinical signs of intestinal disorders: A retrospective study of 116 cases. Equine Vet J 28:275-284, 1996.
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Affiliation of the authors at the time of publication
1College of Veterinary Medicine Auburn University Auburn, AL, USA and 2Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, USA.
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