Abdominal Ultrasonography in the Equine Patient With Acute ... · with the ventral colon...

Abdominal Ultrasonography in the Equine PatientWith Acute Signs of Colic

Andreas Klohnen, DVM, Diplomate ACVS

Author’s address: Chino Valley Equine Hospital, 2945 English Place, Chino Hills, CA 91709; e-mail:[email protected]. © 2012 AAEP.

1. Introduction

Abdominal pain in horses is one of the most commonpresenting clinical signs and a major cause of mor-tality in horses. Rapid and effective evaluation ofhorses with signs of colic is necessary for promptsurgical intervention, thereby allowing for more suc-cessful outcomes. However, determining the ac-tual cause of colic in horses is a diagnostic challenge,and the decision for selecting abdominal surgery inhorses with colic is not always straightforward.Analgesic administration or stoic horses may delaynecessary abdominal surgery, resulting in a de-creased prognosis for survival.

The decision between medical management and sur-gical intervention is largely made on the basis of phys-ical examination, abdominocentesis, abdominalpalpation per rectum and, most importantly, persis-tent signs of abdominal pain despite medical treat-ment. More recently, abdominal radiography andabdominal ultrasonography have become more usefulin evaluating horses with abdominal pain. Severalrecent studies have shown that abdominal ultrasonog-raphy in the colic patient can be a very useful diagnos-tic tool.

Technique

Abdominal ultrasonography is a very safe and non-invasive diagnostic test. After initial examination

of a horse with signs of abdominal pain, the baselinepain level should be considered. An abdominal ul-trasound examination should not be performed if ahorse has fractious behavior or is showing signs ofuncontrollable abdominal pain despite sedation.

The abdominal wall is saturated with isopropylalcohol using a spray bottle to dampen the hair andcreate adequate contact with the transducer toachieve adequate image quality. Ultrasonographiccoupling gel can then be applied liberally to theultrasound transducer to further enhance the imagequality. A 3.5-MHz convex linear transducer witha maximal depth range of at least 25 cm is used forultrasonographic examination of the equine abdo-men. To evaluate the deeper areas of the equineabdomen, the focal zones should be positioned in thefar field to enhance visualization of deeper struc-tures. In most ambulatory settings, a practitionermay not have a 3.5-MHz probe available. A 5-MHZlinear rectal probe may be used instead but will givethe examiner a much smaller ultrasonographic win-dow of the abdomen. The 5-MHz probe does notprovide the same level of penetration as a 3.5-MHzconvex linear transducer, but it is adequate to eval-uate portions of the equine adult abdomen for signsof abdominal pain.

A systematic approach to each ultrasound exami-nation in a horse for signs of colic is recommended.

AAEP PROCEEDINGS � Vol. 58 � 2012 11

IN-DEPTH: ULTRASOUND OF THE THORAX AND ABDOMEN

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Orig. Op. OPERATOR: Session PROOF: PE’s: AA’s: 4/Color Figure(s) ARTNO:

1st disk, 2nd beb spencers 8 F1-3,5-10,12 3407

The abdomen is divided into three regions (rightparalumbar fossa [PLF] region, ventral region/ingui-nal region, and left paralumbar fossa). Each regioncan be further subdivided into right PLF 1, 2, and 3;ventral (V) 1, 2, and 3; and left PLF 1, 2, and 3. Theexamination should start in the right paralumbarfossa and continue to the ventral/inguinal region andthen the left paralumbar fossa region after the horse isturned around or the machine moved to the other sideof the horse. The right and left intercostal regionsshould also be evaluated for possible intestinal abnor-malities. The margins of these regions are meant toserve as a guideline for a systemic ultrasound exami-nation. In most equine cases with colic, an individualregion does not correspond with a specific diagnosis forthe signs of colic.

Abdominal Ultrasound of the Normal HorseIn clinically normal horses without signs of abdom-inal pain, the large intestine can be distinguishedfrom the small intestine by size and appearance.The large colon can be visualized in all three regionsand appears as a bright hyperechoic line correlatingwith the ventral colon sacculations or the wall of thedorsal colon (Fig. 1). Because of the size of thelarge colon and the presence of gas and feed withinthe colon, the deep border is often not visualized andthe colon cannot be imaged as a complete loop.In a normal horse, individual layers of the colon arenot typically visible.

Transverse sections of the small intestine are im-aged as complete loops, and usually more than 1 loopcan be viewed (Fig. 2, A and B). In a normal horse,the small intestine can be imaged as circular densi-ties that show continuous movement. The smallintestine is often visible along the ventral axial sur-face of the spleen from the left side and in theinguinal regions. Small intestine wall thickness inclinically normal horses is difficult to measure whenscanning at maximal depth because it is less than

the width of the measuring cursors (�3 mm). It isvery rare to visualize distended loops of small intes-tine in a clinically normal horse.

The nephro-splenic space is imaged in the left PLF1 region, where the left kidney and caudal edge ofthe spleen are consistently identified (Fig. 3). Thestomach wall should be visualized in the left inter-costal spaces, but the stomach should not be dis-tended with fluid.

Examination of the right PLF 1 region and therightmost caudal intercostal areas should demon-strate the right kidney and the duodenum. In aclinically normal horse, there should not be anysignificant distention or increased wall thickness inthe duodenum.

In a clinically normal horse, the ventral region(V1, just caudal to the sternum) may demonstratethe presence of abdominal fluid.

Abdominal Ultrasound of the Horse With Signs ofAbdominal PainAbdominal ultrasound in the horse with signs ofabdominal pain has been most helpful for the detec-

Fig. 1. Large colon wall.

Fig. 2. A, Distended loop of small intestine. B, Several distendedloops of small intestines.

12 2012 � Vol. 58 � AAEP PROCEEDINGS


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tion and diagnosis of strangulating and nonstrangu-lation lesions of the small intestine. Each regionand subregion of the abdomen is examined ultra-sonographically, and the detection of either largeintestine and/or small intestine is recorded. Im-ages of the small intestine (jejunum) and duodenumare measured for diameter and wall thickness.The detection of intestinal motility is recorded.Small intestinal motility is defined as contractionand subsequent distention of the small intestinalwalls with a change in luminal diameter. In somehorses with small intestinal lesions, there is com-plete absence of small intestinal motility.

Additionally, the nephro-splenic space (left PLF land left PLF 2) is evaluated for either a left dorsalcolon displacement or a nephro-splenic entrapmentof the large colon. The left intercostal spaces (ribs10 to 13) are also evaluated for possible distention ofthe stomach with fluid (gastric reflux).

Horses With Sand Accumulation in the Colon (Sand Colic)Abdominal ultrasonography of a horse with sandcolic usually will not show any distended, amotileloops of small intestine. Some horses with sandcolic may show signs of minimally distended smallintestine loops filled with fluid or ingesta, which aresubsequent to the primary sand colic problem.The gold standard for the detection of sand in thelarge colon is abdominal radiography (Fig. 4). Ab-dominal ultrasound of a horse with sand accumula-tion in the colon will reveal the large colon wall inthe ventral region to appear “brighter” and morehyperechoic. This ultrasonographic finding is re-lated to the ultrasonographic reflection of the sandparticles (Fig. 5).

Horses With Large Colon Enteroliths and/or Small ColonEnterolithsAbdominal ultrasonography of a horse with a largecolon enterolith or small colon enterolith usuallywill not show any distended or amotile loops of smallintestine but may show minimally distended loops of

small intestine that are secondary to the primaryproblem (colonic enterolith). The gold standard forthe detection of an enterolith in the large colon isabdominal radiographs. In the author’s opinion,colonic enteroliths are not detectable with abdomi-nal ultrasound.

Horses With Peritonitis, Ruptured Intestines, AbdominalFluid AnalysisAbdominal ultrasonography of a horse with perito-nitis will usually show several slightly distendedloops of small intestine with a very thickened small

Fig. 3. Normal anatomy of the left paralumbar fossa.

Fig. 4. Sand accumulation in the colon.

Fig. 5. Ultrasonographic view of the large colon wall in theventral region showing evidence of sand in the colon.



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intestinal wall (Fig. 6). The small intestinal motilitymay vary. The thickened loops of small intestine areusually best visualized in the ventral or inguinal re-gions. The ventral 1 region (close to the sternum)may reveal an increased amount of abdominal fluid.The abdominal fluid may be “gray” or hazy in appear-ance. In some horses, it is possible to visualize theactual cause of the peritonitis such as an intestinal ormesenteric abscess (Fig. 7, A and B).

A horse with intestinal rupture will have a vary-ing amount of increased abdominal fluid and vary-ing stages of distended and edematous loops of smallintestine (Fig. 8). The appearance may vary, de-pending on the time interval from rupture to abdom-inal ultrasound examination.

Abdominal ultrasonography can be helpful in lo-cating an area in the ventral abdominal region withan increased amount of abdominal fluid, in order toperform abdominocentesis (Fig. 8). Normal abdom-inal fluid should appear anechoic or “black” on theultrasound screen.

Gastric Distention With Fluid (Reflux)

The equine stomach is located between ribs 10 and13 on the left side of the abdomen. It is the author’sopinion that a normal equine stomach will not showany evidence of gastric fluid. The outer wall of thestomach can be identified and shows a similar ap-pearance as the wall of the large colon. Once thestomach is filled with fluid or reflux, the lesser andgreater curvature will become visible during an ul-trasonographic examination (Fig. 9). The amountof gastric distention seen on ultrasound will dependon the quantity of gastric reflux. A horse with adistended, fluid-filled stomach should have a stom-ach tube placed to further evaluate the horse for thepresence of gastric reflux.

Horses With Anterior EnteritisAbdominal ultrasonography of a horse with anteriorenteritis usually will reveal a fluid-filled stomach

Fig. 6. Slightly distended loops of small intestine with verythickened intestinal wall, indicative of peritonitis.

Fig. 7. A, Abdominal ultrasound of a horse with an intra-abdom-inal abscess. B, Abdominal ultrasound of a horse with a largeintra-abdominal abscess.

Fig. 8. Abdominal ultrasound view of the ventral region indicat-ing an increased amount of abdominal fluid.



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caused by gastric reflux on the left side of the abdo-men. The duodenum is usually also distended andmay appear edematous and possibly amotile. Theduodenum is visible cranial to the right paralumbarfossa 1 region in the right caudal intercostal spaces.Further examination of the right paralumbar fossaand ventral region will reveal several slightly dis-tended but very edematous loops of small intestinewith decreased motility. A horse with anterior en-teritis may have an increased amount of abdominalfluid in the cranioventral abdominal region.

Horses With Strangulating Obstruction of the SmallIntestineAbdominal ultrasonography of a horse with a stran-gulating obstruction of the small intestine will showseveral distended loops of small intestine adjacent toeach other (three to eight loops of small intestine perfield) with either slow small intestinal motility or nosmall intestinal motility (Fig. 10). Some of the dis-tended loops of small intestine can be thickened oredematous. Most of the distended loops of smallintestine can be visualized in the right lowerparalumbar fossa region (right PLF 3), ventral re-gions, or inguinal regions. The cranial abdomenmay reveal an increased amount of free abdominalfluid, and the stomach may be filled with gastricfluid due to reflux.

Horses With Large Colon TorsionIn most horses with a large colon torsion or volvulus,an abdominal ultrasound cannot be performed be-cause many horses with a colon torsion show signs ofuncontrollable abdominal pain despite sedation.If an abdominal ultrasound can be performed, thelarge colon wall visualized in the right paralumbarfossa or the ventral region will be very edematous(�8 mm thick). The colonic vessels seen in theright paralumbar fossa region can be dilated andedematous.

Horses With Right Dorsal Colon DisplacementHorses with a right dorsal colon displacement willnot have a distinct ultrasonographic appearance.There may be many slightly distended loops of smallintestine that are filled with ingesta. The smallintestinal changes seen are usually secondary to theprimary large intestinal problem. The colonic wallusually is not edematous, but the colonic vesselsmay be very distended in the right paralumbar fossaregion, and the vessel walls may be edematous.

Horses With Nephro-Splenic Entrapment of the LargeColon and Left Dorsal Colon DisplacementAbdominal ultrasonography in horses with a “true”nephro-splenic entrapment of the large colon, de-fined as colon located in the nephro-splenic spacebetween the dorsal edge of the spleen and the leftkidney, the left kidney cannot be visualized, thetypical appearance of the rounded, caudodorsal bor-der of the spleen is lost, and a colonic gas shadow isseen next to the dorsal edge of the spleen (Fig. 11).Horses may have varying amounts of gastric fluidand may have signs of slightly distended loops ofsmall intestine with reduced small intestinal motil-ity; however, these small intestinal changes are sec-ondary to the primary large intestinal problem.

In horses with a left dorsal colon displacement,defined as colon located dorsal to the spleen and notin the nephro-splenic space, the left kidney mayeither be fully visualized or only partially visualized.The typical appearance of the rounded, caudodorsal

Fig. 9. Distended stomach with gastric reflux.

Fig. 10. Multiple distended loops of small intestine with noevidence of motility indicating a strangulation obstruction.



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border of the spleen is either completely or partiallylost, and a colonic gas shadow is seen next to thedorsal edge of the spleen. The entire dorsal edge ofthe spleen cannot be visualized from cranial to cau-dal, and instead colon wall will be seen (Fig. 12).Usually these horses respond to treatment with in-travenous fluid therapy and intravenous phenyleph-rine therapy. Upon resolution of the displacement,the dorsal edge of the spleen will become visible nextto the left kidney on consecutive abdominal ultra-sound exams.

Validation of Abdominal Ultrasonography for Horses WithAbdominal PainDuring a 7.5-year study period, the following proce-dures were performed on horses admitted to ChinoValley Equine Hospital for signs of colic: physicalexamination, complete blood count (CBC), abdomi-nal fluid analysis (total protein, cytologic exami-nation, white blood cell count), placement of anasogastric tube to obtain gastric reflux, abdominalpalpation per rectum by a senior clinician, abdomi-

nal radiography, and ultrasonographic examinationof the abdomen. Horses were excluded from thestudy if they were unable to be examined ultrasono-graphically because of fractious behavior or uncon-trollable abdominal pain.

During the study period, 3092 horses with signs ofcolic were evaluated with abdominal ultrasonogra-phy. Of these horses, 1526 were treated medically(49.4%), 1477 underwent exploratory celiotomy(47.8%), and 89 horses were euthanatized (2.9%).

Medical CasesOf the medically treated horses, 436 of 1526 (28.6%)had no small intestine visualized during the abdom-inal ultrasound examination, and 1080 (70.8%) hada few normal-appearing loops of small intestine vi-sualized. Several very small loops of small intes-tine were detected next to the ventral edge of thespleen and/or in the caudal inguinal region. Forty-one (3.8%) appeared to have a gas shadow next tothe dorsal edge of the spleen and were treated med-ically for a possible left dorsal colon displacement.Ten (0.6%) horses appeared to have increased num-bers of distended small intestine loops but showedgood motility.

Euthanasia With Postmortem Examination GroupForty-six of 89 euthanatized horses (51.7%) did notappear to have any distended loops of small intes-tine on abdominal ultrasound. Necropsy examina-tion confirmed that the cause of the colic wasunrelated to the small intestine.

In 43 euthanatized horses (48.3%), abdominal ul-trasound revealed distended loops of small intestine.In 33 of these horses, an ultrasonographic diagnosisof a strangulation obstruction was made and con-firmed during necropsy examination. The remain-ing 10 horses appeared to have small, veryedematous loops of small intestine secondary toperitonitis from a ruptured viscus.

Surgical Small Intestine GroupA strangulation obstruction was diagnosed in 255horses with the help of abdominal ultrasound and

Fig. 11. Abdominal ultrasounds of a horse with a nephro-splenic entrapment of the large colon.

Fig. 12. Ultrasound of the left flank region and left paralumbarfossa region demonstrating large colon wall instead of the spleen.



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confirmed during exploratory celiotomy. All 255cases required a small intestinal resection and anas-tomosis. A diagnosis of nonstrangulating small in-testinal obstruction was made in 141 horses. In139 of these horses, the primary cause of colic wasconfirmed to be related to the small intestine onexploratory celiotomy and required a small intesti-nal resection. Two horses of the 141 horses werefound to have a primary large colon problem with asecondary small intestinal component.

In 49 horses, the abdominal ultrasound revealedseveral small but very edematous loops of smallintestine. In every case, an exploratory celiotomyconfirmed the preoperative diagnosis of abnormalsmall intestine.

Surgical Large Intestine Group

In 555 horses, a preoperative abdominal ultrasoundrevealed no evidence of small intestinal abnormali-ties. In 412 horses, preoperative ultrasound re-vealed mainly findings related to the large intestine,with only a few loops of small intestine that showedminimal small intestinal distention. In all 412cases, exploratory celiotomy confirmed the ultra-sonographic findings of a large intestinal lesion.In 14 cases, a preoperative ultrasonographic diagno-sis of a left dorsal colon displacement was made.None of these horses responded to medical therapy,and an exploratory celiotomy confirmed left dorsalcolon displacement. In 51 cases, a preoperativepresumptive diagnosis of nephro-splenic entrap-ment of the large colon was made on the basis ofabdominal ultrasound. In all 51 cases, the preop-erative findings were confirmed.

2. Discussion

Previous studies have confirmed the utility of ab-dominal ultrasonography for the evaluation ofhorses with signs of colic. In one study, Klohnen etal1 evaluated the use of diagnostic ultrasonographyin horses with signs of acute abdominal pain. Inthis study, abdominal ultrasonography showed100% sensitivity and specificity to diagnose strangu-lation obstructions of the small intestine.

In the current study described in this report, ab-dominal ultrasonography was very helpful to distin-guish between medical problems and surgicaldisorders of the large colon and small intestine.In horses with medical colic or in horses with largecolon disorders, either no small intestinal distentionor only multiple loops of slightly distended smallintestinal loops were seen. Overall, this large caseseries validates the utility of abdominal ultrasonog-raphy in the evaluation of equine colic patients.Most importantly, abdominal ultrasonographyshould be recognized as extremely valuable to deter-mine strangulating obstructions of the smallintestine.

Abdominal Ultrasound to Detect and MonitorPostoperative Ileus

Postoperative ileus is an important cause of morbid-ity and mortality in the postsurgical period forhorses with colic. The diagnosis has classicallybeen made on the basis of postoperative reflux ob-tained through nasogastric intubation and postoper-ative signs of abdominal pain in conjunction withreflux. According to the veterinary literature, post-operative ileus has mainly been defined by the vol-ume of reflux that is recovered from a horse duringa 24-hour period. Abdominal ultrasonography is aproven diagnostic modality in the preoperative diag-nosis of small intestinal lesions and is potentially auseful diagnostic imaging technique to assess dis-tention, contractility, wall edema, and motility ofsmall intestine after surgery. In a study of 830postoperative cases at our clinic, postoperative ileuswas defined as the presence of multiple (n � 3)distended loops of small intestine with decreasedintestinal contractility and motility. Horses wereevaluated every 24 hours after surgery until therewas no further evidence of small intestinal disten-tion. After the diagnosis of ileus was established,horses were treated with a slow IV lidocaine bolus(1.3 mg/kg over 15 minutes) followed by an infusionof 0.05 mg/kg per minute of lidocaine in saline untilcomplete ultrasonographic resolution of postopera-tive ileus was achieved. Of the 213 horses thatshowed ultrasonographic evidence of postoperativeintestinal ileus, 130 (61%) had no evidence of naso-gastric reflux, whereas 83 horses (39%) had reflux.Sixty-seven of these horses (32%) were diagnosedwith a large intestinal lesion, representing 19% ofhorses with a primary diagnosis of large intestinaldisease during the study period. Sixty-eight per-cent (146 horses) were diagnosed with a primarysmall intestinal lesion, which represented 37% ofhorses with a primary diagnosis of small intestinedisease.

We have found that abdominal ultrasound is areliable method for the diagnosis and monitoring ofpostoperative intestinal ileus and may provide amore useful indicator than volume of gastric reflux.

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