IN-DEPTH: COLIC


in which circumstances of the safety of the patient and/or veterinarian is likely to be compromised. Very large horses may be also difficult to palpate, especially for smaller veterinarians. It is esti- mated that the caudal 1/3 of the abdominal contents are available for examination via palpation,3 but veterinarians palpating large horses or veterinari- ans with short arms may find that only 1/4 of the abdominal contents can be reached. In addition, a late term fetus, bladder distention, or colonic and cecal gas distention may obstruct palpation of other structures. The most dreaded complication of rectal palpation


is rectal tear. Specific breeds, horses 9 years of age, and mares have been shown to be at increased risk for this complication.4 The evaluation and treatment of rectal tears have been covered else- where in numerous excellent resources.3–7 Al- though we as veterinarians are often more concerned about potential concerns to our patient’s well-being, another potentially serious consequence of rectal palpation of a horse is injury to the veteri- narian through kick or crush injury. Care must be taken in providing the safest environment for both patient and practitioner. Ultrasound is a portable noninvasive imaging mo-


dality. It is estimated that the peripheral 2/3 of the abdomen of an average horse can be sonographically imaged with a percutaneous technique.8,9 Most ab- dominal sonography is performed percutaneously, but scanning per rectum can also augment the in- formation gathered during rectal palpation, espe- cially when the left kidney, urinary bladder, ureters, reproductive tract, or caudal abdominal vasculature are suspected as causes of abdominal pain. A good working knowledge of abdominal anatomy and im- age optimization is necessary to obtain diagnostic sonographic images in colic cases; that said, with practice and guidance, abdominal sonography is not difficult to learn. Newer protocols for scanning acute colic cases, such as the fast localized abdomi- nal sonography of horses exam,10 provide guidance for performing rapid, consistent examinations that yield useful information in these cases. As with any diagnostic modality, there are limita-


tions to the application of sonographic evaluation to colic. Image quality can be affected by hydration, perfusion, and ambient temperature, as well as the horse’s skin thickness and density, degree of adipos- ity, and haircoat. Patient preparation, which in- cludes grooming, clipping the hair if needed, and the application of gel or isopropyl alcohol, is necessary for adequate image quality. Gas within the bowel prevents sound wave penetration and so the greater the gas distention of the viscera, the fewer struc- tures that may be imaged. Not all ultrasound units have battery power, so access to a power source may be required. In addition, although more affordable units and probe options are becoming increasingly available, there is cost involved in obtaining opti- mum equipment. However, even using a standard


206 2014  Vol. 60  AAEP PROCEEDINGS


rectal probe, some useful information may be obtained.


3. Evaluation of the Large Colon and Cecum


Diseases of the large colon are common causes of colic and include impaction, spasm, displacement, volvulus, intussusception, and colitis/typhlitis. Impaction of the large colon, particularly the pelvic flexure, is easily palpated per rectum, as is impac- tion of the cecum.1,3–5 Impactions are less likely to be identified using ultrasound than via palpation. Large colon displacement and volvulus comprised 1/3 of all cases requiring surgical intervention in one study.11 For conditions such as displacement or volvulus of the large colon, the band direction of the colons may be palpated, although severe gas disten- tion may confuse the findings. In normal horses, palpation per rectum of the nephrosplenic area reveals the left kidney, the spleen, and the nephrosplenic ligament. In horses with nephrosplenic entrapment, the colon is palpa- ble dorsal to the ligament and the spleen may feel enlarged and/or displaced medially and ventrally by the colon. Sonographic evaluation reveals gas- filled bowel dorsal to the spleen, with the view of the kidney partially or wholly obscured. The spleen is displaced ventrally and the dorsal border of the spleen has a straight horizontal border that extends from the paralumbar fossa to the 10th to 12th inter- costal space.8 Right displacement of the colon is characterized


on rectal palpation as colonic bands coursing hori- zontally across the abdomen and the colon may be detected lateral to the cecum. However, severe gas distention in the colon can obscure the exam find- ings. The additional sonographic identification of colonic vessels on the right side of the abdomen is highly sensitive and specific for right dorsal dis- placement or 180° colon volvulus.12 In cases of vascular compromise and inflamma-


tion, sonographic assessment can add diagnostic and prognostic information, which is critical when providing information to clients leading to surgical decisions. Colonic wall thickness has been shown to be a predictor of colonic volvulus and may help to differentiate this condition from simple displace- ment.13 Colon wall edema may be present in cases of vascular compromise and tissue inflammation, which may be seen in chronic severe impaction or colitis; the changes in the latter scenarios are gen- erally much less severe than in a strangulating le- sion. Having information about colon wall health or compromise is useful when trying to form a prog- nosis to advise clients and set expectations. Colonic intussusception is rare, but ileocecal, ce- cocecal, and cecocolic intussusception have been re- ported in adult horses.14 On rectal palpation, the intussusception may be occult or manifest as a mass in the right abdomen.1,3,4,14 Sonographically, a classic “target lesion” appearance is noted in the right paralumbar region. The outer loop (intussus-


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