Will rapid abdominal ultrasound help you to decide whether to take a colic to surgery?

Rapid abdominal ultrasonography is frequently used in the evaluation of human trauma patients to determine the need for exploratory laparotomy. Over the last 2 decades it has been applied to the preliminary assessment of the horse with acute abdominal pain where the initial objective is to differentiate surgical from nonsurgical lesions. Targeted examination techniques have been described that evaluate intestinal motility, wall thickness and luminal contents, the volume of pleural and peritoneal fluid, size of the stomach and the ability to visualise the left kidney. Equine colic AND ultrasound AND surgery Equine colic AND ultrasound AND diagnosis Studies that investigated the diagnostic accuracy of abdominal ultrasonography in horses with colic were critically evaluated. In one prospective study the outcome was defined as need for surgery (Busoni et al. 2011) whereas the remaining 7 studies used a definitive diagnosis for categorising outcome. Therefore the research question was refined to determine the ability of ultrasound to specifically diagnose strangulating small intestinal lesions, large colon volvulus, left and right displacements of the large colon. The sole study that combined data for all surgical cases is limited by the small samples size, as only 13 horses were defined as surgical, this precluded statistical comparisons for many abnormal ultrasound findings other than dilated turgid loops of small intestine. As data for all surgical cases is combined the apparent sensitivity of abnormal findings is lower than in other studies where specific diagnoses are used as outcome. In the study mentioned above and those studies discussed below, the results reflect findings in a referral population. In all of the reported studies the results reflect findings in a referral population, where the ultrasonographer was not blinded to other clinical findings at admission. As the prevalence of lesions will be different in first opinion practice the PPV and NPV may vary from those reported (Table 1). Specificity % Two studies evaluated the significance of distended small intestine (DSI) on ultrasound in the diagnosis of strangulating small intestinal lesions (Klohnen et al. 1996; Beccati et al. 2011). In Beccati et al. (2011) a definitive diagnosis was confirmed at surgery or post mortem examination therefore a bias for including more severe cases likely exists, whilst in Klohnen et al. (1996) 74 cases responded to medical management and therefore a definitive diagnosis was not confirmed (Table 2). Specificity % Prospective n = 226 and n = 20 normal controls Beccati et al. 2011 Perugia Retrospective n = 158 Strangulating small intestinal lesion n = 45 Three case series evaluated the diagnostic value of abdominal ultrasound in diagnosing LDDC (Santschi et al. 1993; Beccati et al. 2011; Busoni et al. 2011). In Santschi et al. (1993) the diagnosis was not confirmed using a different method such as rectal examination in a proportion of the cases, therefore it is not appropriate to extrapolate predictive values (Table 3). Specificity % Beccati et al. 2011 Perugia Retrospective n = 158 Busoni et al. 2011 Liege Santschi et al. 1993 Florida Two studies have evaluated colon wall thickness in diagnosing large colon (LC) volvulus (Pease et al. 2004; Beccati et al. 2011), in which the diagnosis was confirmed at post mortem examination or exploratory laparotomy. Pease et al. (2004) used other LC disorders as the control group whilst all other diagnoses were used in Beccati et al. (2011). Another small case series describes the absence of ventral sacculations in 4 horses with LC volvulus (Abutarbush 2006) (Table 4). Specificity % Beccati et al. 2011 Perugia Retrospective n = 158 LC volvulus n = 9 Pease et al. 2004 Cornell Prospective n = 40 Thickness of large colon: >9 mm LC volvulus n = 12 Abutarbush 2006 Saskatoon Descriptive n = 4 Two studies describe the presence of abnormal colonic vessels on the right side of the abdomen in diagnosing right dorsal displacements (RDDC) or 180 degree colon torsions (Grenager and Durham 2011; Ness et al. 2012). In both studies the diagnosis was confirmed at surgery. A control group of surgical colics without RDDC/180 degree volvulus was included by Ness et al. (2012), but there was no control group in Grenager and Durham (2011) (Table 5). Specificity % Ness et al. 2012 Cornell Retrospective n = 82 Grenager and Durham 2011 California Descriptive n = 23 The presence of amotile turgid small intestinal loops is highly specific for a surgical colic lesion and more sensitive for a strangulating small intestinal lesion. An inability to visualise the left kidney is poorly predictive of a left dorsal displacement of the large colon due to the number of false positives observed in 2 studies, whereas visualising the left kidney is more useful in ruling out a LDDC. Thickened large colon wall (>9 mm) in the ventral abdomen is very specific for a large colon volvulus whilst visualisation of abnormal colonic vessels on the right of the abdomen are highly specific for right dorsal displacement or a 180 degree colon volvulus. There is moderate evidence that abdominal ultrasonography is a useful adjunct in the preliminary evaluation of the equine colic patient. Larger scale prospective studies are needed to confirm these preliminary findings, particularly to determine the value of ultrasound for diagnosing large colon displacements. No conflicts of interests have been declared.

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