Ultrasound of the Nonacute Abdomen: Gastrointestinal Tract · Ultrasound of the Nonacute Abdomen:...

Ultrasound of the Nonacute Abdomen:Gastrointestinal Tract

Virginia B. Reef, DVM

Author’s address: Department of Clinical Studies, New Bolton Center, University of Pennsylvania,382 West Street Road, Kennett Square, PA 19348-1692; e-mail: [email protected]. © 2012 AAEP.

1. Introduction

Ultrasonography is invaluable in the diagnosis of awide variety of gastrointestinal diseases in horsesand determining if the horse has a medical or sur-gical lesion. The quick evaluation of the abdomenin horses with severe colic (FLASH examination) isan examination of selected high-yield areas of theabdomen that can be done in the emergency settingin less than 15 minutes by individuals who are notextensively trained in diagnostic ultrasound.1 Thewindows for the FLASH scan of the emergency ab-domen include the left middle third of the abdomen,the renosplenic window, the gastric window, theventral abdomen, the duodenal window, the rightmiddle third of the abdomen, and the right cranio-ventral thorax.1 In postoperative ponies, bowelhandling during exploratory celiotomy caused min-imal changes in bowel wall thickness, contractility,amount of distention, luminal contents, and perito-neal fluid.2 Therefore, abnormal gastrointestinalmotility, size or contents; bowel wall thickness,and/or changes in the quantity or echogenicity of theperitoneal fluid are clinically significant in a postop-erative patient. A complete sonographic examina-tion is also very useful in evaluating the horse withchronic colic, chronic weight loss, or when other

abdominal disease is suspected. Sonographic eval-uation of the abdomen is also valuable for followingthe clinical progress in horses with a wide variety ofgastrointestinal diseases.

The sonographic examination of the gastrointesti-nal tract can be performed with a microconvextransducer, a high-frequency linear transducer forevaluation of bowel wall thickness close to the bodywall, and a transrectal transducer for evaluatingany abnormalities detected on rectal examination.A large lower-frequency convex transducer is usefulfor the FLASH examination, in which time is of theessence in making the diagnosis and the subtletiesof the image are less important, or for evaluatinggastrointestinal structures that are further awayfrom the transducer. The standard linear transrec-tal transducer can be used and placed over anystructure that is abnormal on rectal palpation tofurther define the abnormality but is limited bythe depth of penetration of the transducer and theability to place the transducer directly over theabnormality. A small microconvex transducercan also be used transrectally and has the advan-tage of a wide field of view and being able to directthe transducer towards the abnormality withouthaving to place the transducer directly over theabnormality.

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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 11 1,3,5-11,13-16,18 3288

2. Normal Ultrasonographic Findings in the EquineGastrointestinal Tract

The large intestinal echoes are recognized by theirlarge semicurved, sacculated appearance, except forthe right dorsal colon which has a smoother nonsac-culated appearance and is imaged consistently inthe right 11th and 12th intercostal spaces in bothnormal horses and horses with right dorsal colitis.3

The large intestinal wall is hypoechoic to echogenicwith a hyperechoic mucosal gas echo and measures�3.5 mm in the adult horse. Peristaltic activity isnormally visualized. The cecum has larger con-tractions and a trend towards smaller sacculationscompared with the large colon in normal horses.4

The small intestine has a small tubular and circularappearance with a hypoechoic to echogenic wall thatusually measures �3 mm in the equine adult. Per-istaltic waves are also normally visualized. Theduodenum is imaged around the caudal pole of theright kidney and medial to the right liver lobe.It appears small and circular with a hypoechoic toechogenic wall, also measures �3 mm, and appearspartially collapsed with its peristaltic motion easilyvisualized. Jejunal, cecal, and colonic motility isdecreased with fasting.5 The gastric fundic echo isvisualized in the left 9th to 12th intercostal space andis imaged as a large semicircular structure medial tothe spleen at the level of the splenic vein. Thegastric wall is hypoechoic to echogenic with a hyper-echoic gas echo from the mucosal surface and nor-mally measures �7.5 mm. All the wall thicknessesin normal adult ponies are significantly thinnerthan in the normal adult horse.2

Large intestinal motility was significantly re-duced (most marked in the aboral left ventral colon)in stabled horses compared with pastured horses.6

Xylazine in fasted horses decreased jejunal and ce-cal motility.5 Romifidine has been shown to resultin decreased motility (nonpropulsive contractions) ofthe jejunum, cecum, and left ventral colon.7 Bothfeeding status and sedation need to considered whenevaluating GI motility in horses.5

3. Gastrointestinal Diseases

Right Dorsal Displacement of the Large ColonAbnormal positioning of the gastrointestinal viscerais difficult to diagnose ultrasonographically, unlessthe viscera are displaced into the scrotum, thoraciccavity or into an umbilical hernia. Right dorsaldisplacements have traditionally been difficult todefinitively diagnose. Horses with a colonic dis-placement and an elevated gamma-glutamyl trans-ferase (GGT) are most likely to have a right dorsaldisplacement of the large colon (RDDLC).8 Thesuccess of treating horses with right dorsal displace-ments has been reported to be 64% in a recentstudy.9 In this study, right dorsal displacementwas diagnosed by the identification of a gas dis-tended colon oriented horizontally across the abdo-men on rectal palpation and the sonographic finding

of a large gas filled large colon.9 The detection ofabnormally located large colon mesenteric vessels,distinct from cecal vessels, along the right lateralabdomen, dorsal to the costochondral junction in atleast 2 intercostal spaces (between intercostal space10 to 16) is consistent with a surgical diagnosis ofright dorsal displacement of the large colon (Fig.1).10 This finding was not seen by these investiga-tors in other types of surgical colics. Althoughthese investigators did not see these abnormallylocated mesenteric vessels in the right lower abdom-inal area in horses with a large colon volvulus, thisremains a possibility.10

Colon/Cecal ImpactionThe reduction in motility in the aboral portion of theleft ventral colon detected in stabled horses com-pared with pastured horses may provide insight intothe reason for the most common impaction at thepelvic flexure.6 An impaction can often be imagedfrom the flank for side of the abdomen in horses withcecal or large colon impactions. The impacted vis-cus is enlarged and may appear flattened, or roundto oval (Fig. 2). The distended large colon will oc-cupy a much larger area in the abdomen than nor-mal, often measuring 20 to 30 cm or more, and thesacculations are reduced or not visible. The bowelwall may be normal thickness or may be thickerthan normal, and there is a large acoustic shadowcast from the impacted ingesta. The hyperechoicecho from impacted ingesta appears as a long flatthick hyperechoic line in an enlarged elongated vis-cus. Little to no motility of the affected portion ofthe intestinal tract will also be imaged. Small co-lon impactions may be imaged transrectally as echo-genic intraluminal masses.

IntussusceptionsIntussusceptions have a characteristic target orbull’s eye sign in the affected portion of intestine

Fig. 1. Sonogram of the abdomen in the right 13th intercostalspace above the costochondral junction in a horse with a rightdorsal displacement. Notice the large distended colonic mesen-teric vessel (arrow) located just underneath the diaphragm andwas best imaged during exhalation.

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(Fig. 3).11–13 With intussusceptions involving thelarge bowel, the affected segments are markedlythickened, diminishing the typical sacculated ap-pearance of the large colon and cecum. The outerintussuscipiens has an echoic pattern within thewall typical of large bowel and a somewhat saccu-lated appearance. The inner intussusceptum isthick-walled, hypoechoic to echoic with loss ofbowel wall layering and surrounded by fluid and/orfibrin. The majority of intussusceptions imaged inadult horses are imaged from the right ventralabdomen.11–13 The cecocolic intussusceptionshave a more oval appearance than the ceocecalintussusceptions.14

Small Intestinal MassesMasses within the intestinal wall are thickened ar-eas, often compromising the lumen of the affectedportion of intestine, which may be anechoic to echo-genic, depending on their etiology. Intramuralhemorrhage has been reported in horses causingsmall intestinal obstruction (Fig. 4).15 Hemor-rhage in the lumen of the intestine often appears asechogenic clots or echoic swirling fluid.15 Areas ofmural stricture have been imaged in several horseswith chronic colic.

Idiopathic Muscular Hypertrophy of the SmallIntestineMarked symmetrical annular thickening of the mus-cular layer of the small intestine has been reportedin horses with idiopathic muscular hypertrophy ofthe small intestine, resulting in reduction of theluminal diameter during peristalsis (Fig. 5).13,16

The ileum is the most commonly affected. Severelythickened loops may be present adjacent to mildlythickened loops of small intestine. A significantreduction in intestinal motility occurs in those se-verely thickened loops which appear tubular andnoncompressible.

Inflammatory Bowel DiseaseThe wall of the affected portion of the intestine isusually thickened with an abnormal pattern of echo-genicity in the bowel wall (Fig. 6). Increased ordecreased echogenicity in one or more layers of thebowel wall, usually the submucosa, is usually pres-ent. The visualization of abnormal echogenicitywith persistence of the bowel wall layering is moreconsistent with inflammatory bowel disease (IBD)

Fig. 2. Sonogram of the right dorsal abdomen in the 15th inter-costal space in a horse with a large cecal impaction. Notice thelarge oblong ingesta filled cecum (arrows). This viscus extendedcranially from the paralumbar fossa to the 12th intercostal space.

Fig. 3. Sonogram of the right 17th intercostal space in a horsewith a cecocolic intussusception. Notice the thickened outer in-tussuscipiens (large arrow) and the thickened inner intussuscep-tum (small arrow) with the hypoechoic material in betweencreating a target or bull’s eye sign.

Fig. 4. Sonogram of the ventral abdomen obtained from a horsewith an intramural hematoma (arrows). Notice the markedlythickened jejunum with the hypoechoic to echoic material in thewall of the intestine which was seen to be swirling in real time.



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than neoplasia. Thickening of the bowel wall withincreased vascularity is indicative of active IBD.Power Doppler and color Doppler ultrasound can beused to assess vascularity of the gastrointestinaltract in horses with suspected IBD. Although usu-ally diffuse, focal eosinophilic enteritis causingsmall intestinal obstruction has been described insome horses.17 A segmental mural lesion in the leftdorsal colon, causing partial obstruction of the largecolon, has also been reported.18 Circumferentialmural bands have been detected in both the smalland large intestine at surgery in some horses withIBD.19

Necrotizing EnterocolitisSonography can characterize the peritoneal fluid,identify intramural gas (pneumatosis intestinalis),portal venous gas, intraperitoneal gas, bowel wallthickening, and bowel wall perfusion in foals and

adults with necrotizing enterocolitis. Pneumatosisintestinalis is the detection of hyperechoic echoesconsistent with free gas in the intestinal wall (Fig.7). Thinning of the bowel wall and lack of bowelwall perfusion are indicative of nonviable intestineand possible impending perforation.

Right Dorsal ColitisRight dorsal colitis associated with nonsteroidal an-ti-inflammatory drug toxicity can be diagnosed ul-trasonographically by detecting a thickened rightdorsal colon ventral to the liver in the right 10th to14th intercostal spaces.3,12,13,20,21 The right dorsalcolon can consistently be imaged in the right 11th

and 12th intercostal spaces in all horses with rightdorsal colitis and in the 13th intercostal space inmost affected horses.3 The wall of the right dorsalcolon is usually thickened (2 to 3 times normal) andis significantly greater than the thickness of theright ventral colon measured in the 12th intercostalspace in affected horses.3 An abnormal pattern ofechogenicity of the right dorsal colon is detectedsonographically when compared with control horses.In affected horses, a hypoechoic layer was detectedin the thickened right dorsal colon, surrounded oneach side by a hyperechoic mucosal and serosal sur-face (Fig. 8).3 The hypoechoic layer was less echoicthan the adjacent liver. In this study, the hy-poechoic layer detected in the wall of the right dorsalcolon in all horses with right dorsal colitis appearedto correspond to submucosal edema, inflammatorycell infiltrates, and granulation tissue that weresubsequently observed on postmortem examina-tion.3 Thinning of the wall of the right dorsal colonwas reported in one horse treated successfully forright dorsal colitis, as well as in one horse that hada rupture of the right dorsal colon.3 The sensitivityand specificity of the ultrasonographic detection of

Fig. 5. Sonogram of the right ventral abdomen obtained from ayearling with ileal hypertrophy. Notice the markedly thickenedilium (arrow) with thick hypoechoic muscular layer.

Fig. 6. Sonogram of the right ventral abdomen in a horse withinflammatory bowel disease. Notice the marked thickening ofthe right ventral colon up to 7.6 mm. Also notice the largesubmucosal layer (arrows).

Fig. 7. Sonogram of the left paralumbar fossa in a horse withpneumatosis intestinalis associated with a necrotic area in theileum. Notice the hyperechoic pinpoint echoes representing gas(small arrow) dissecting through the wall of the ileum (largearrows).



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right dorsal colitis remains to be determined, as doesits usefulness in monitoring the response of horsesto treatment. Affected areas of the right dorsalcolon may not be accessible ultrasonographically,and mural thickness may be within the normalrange in horses with severe ulceration of the rightdorsal colon.3

Verminous ArteritisVerminous arteritis can be imaged if the affectedvessel is imageable transrectally. The affected ves-sel wall is thickened and large plaque-like or masslesions can be imaged along the intimal surface ofthe vessel, invading the arterial lumen.

4. Gastritis/Gastric Ulceration/GastricImpaction/Gastric Rupture

Irregular thickening of the gastric wall with promi-nent rugal folds may be detected in some horses withgastritis. Gastric ulcers cannot usually be imagedultrasonographically but have been seen by the au-thor in one yearling with a severe gastric impaction.Gastric impactions appear as a markedly enlargedstomach that is imageable over many intercostalspaces with ventral and caudal displacement of thespleen (Fig. 9).22,23 Horses with gastric rupturehave an increased amount of flocculent peritonealfluid with large particulate matter and free gaswithin (Fig. 10). The defect in the gastric wallwith thickened curled edges has been detectedultrasonographically.

Fig. 9. Sonogram of the left ventral abdomen in a horse withsevere gastric impaction. Notice the marked enlargement andflattening of the normally circular gastric echo. The stomachextended over 10 intercostal spaces and was displacing the lungdorsally, the spleen ventrally and occupied the area from the midventral abdomen to the dorsal portion of the left side of theabdomen.

Fig. 11. Sonogram of the left 12th intercostal space in a horsewith a gastric myxosarcoma. Notice the large size of the gastricneoplasm (18.93 � 21.43 cm).

Fig. 8. Sonogram of the right 13th intercostal space in a horsewith right dorsal colitis. Notice the marked thickening of theventral aspect of the right dorsal colon (large arrows) with theincreased echogenicity and thickening of the submucosal layer(small arrows).

Fig. 10. Sonogram of the left 13th intercostal space in a horsewith a gastric rupture. Notice the hyperechoic pinpoint echoesrepresenting free gas (small arrows) adjacent to the stomach inthe echoic peritoneal fluid. There is also a pneumoperitoneum(large arrow).



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Gastric NeoplasiaBy the time that the horse exhibits clinical signsassociated with gastric neoplasia, the mass is usu-ally large enough to be easily imaged ultrasono-graphically. In 3 of 4 horses with squamous cellcarcinoma in which an ultrasonographic examina-tion was performed, the mass was large and visibleultrasonographically. In the one horse in whichthe mass was not detected ultrasonographically, thesquamous cell carcinoma was small (2.6 by 4.2cm).24 The masses are usually large and het-eroechoic (Fig. 11). Metastatic neoplasia is com-

mon in horses with gastric neoplasia. Involvementof the adjacent liver and spleen commonly occurswith larger neoplasms. Intra-abdominal masseswere imaged in all 5 horses in one study with gastricneoplasia in which an abdominal ultrasound exam-ination had been performed.24 Squamous cell car-cinoma is the most common gastric neoplasm foundin horses and is usually located in the nonglandularportion of the stomach.24 A gastric myxosarcomaseen by the author had a more homogeneous dis-crete sonographic appearance.

Intestinal NeoplasiaNeoplasms affecting the wall of the gastrointestinaltract may be visualized on transabdominal ultrasono-graphic examination of the abdomen. If abnormalloops of bowel are palpable rectally, rectal ultrasono-graphic examination would enable further character-ization of the mass invading the intestinal wall.

The sonographic identification of a wide variety ofintestinal neoplasia has been described.25 Themost common primary gastrointestinal neoplasia in-cludes intestinal adenocarcinoma, GIST (gastroin-testinal stromal tumors), leiomyoma/myxosarcoma,and alimentary lymphosarcoma. The GIST massesthat have been seen ultrasonographically may beround to oval or multilobular with a heteroechoicsonographic appearance (Fig. 12). Hypoechoic toanechoic areas of necrosis may be imaged within thegastrointestinal mass. Intestinal adenocarcinomahas been imaged sonographically as a solid homoge-neous or heteroechoic intraluminal 3–9 cm mass.In some horses with intestinal adenocarcinoma, onlyincreased wall thickness of the large colon, an omen-

Fig. 12. Sonogram of the left ventral abdomen in a horse with aGIST. Notice the large heterogeneous intestinal mass (arrows).

Fig. 13. Sonograms of the abdomen in a horse withalimentary and splenic lymphosarcoma. Notice thediffuse thickening of the small intestine and the loss ofthe bowel wall layering (arrows) consistent with cellu-lar infiltration of the bowel wall (A), the enlargementand heterogeneity (arrows) of the mesenteric lymphnodes (B), and the hypoechoic mass (arrow) in thespleen (C).



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tal mass or lymphadenopathy were detected sono-graphically. Thickening of the gastrointestinalwall, most frequently the small intestine, with anechoic homogeneous cellular infiltrate is consistentwith alimentary lymphosarcoma (Fig. 13), althoughinflammatory bowel disease must be included in thedifferential list. Loss of the layering of the bowelwall is more indicative of neoplasia, but may also besimply a consequence of the resolution of the sono-graphic image. Large solitary mostly homogeneousmural masses are also occasionally imaged in horseswith lymphosarcoma. Hypoechoic homogeneousenlarged mesenteric lymph nodes are commonly de-tected in horses with lymphosarcoma (Fig. 13).Hepatic and splenic involvement may also be de-tected (Fig. 13). Hemangiosarcoma can occasion-ally be detected in the wall of the gastrointestinal

tract and mimics the sonographic appearance of amural hematoma (Fig 14).

Abdominal AbscessAbdominal abscesses may be anechoic, hypoechoic,or filled with echoic material and may be loculated(Fig. 15). Hyperechoic echoes representing free gasmay be detected suggesting concurrent anaerobicinfection. Mixed homogeneously hypoechoic or het-erogeneous encapsulated abscesses are common inhorses with mesenteric abscesses associated withStreptococcus equi spp. equi.26 Abdominal ab-scesses associated with Streptococcus equi spp. equiwere visualized via transcutaneous and/or transrec-tal ultrasonography in all horses.26 Abscesseswere identified throughout the caudal abdomen(ventral to the left kidney, in the dorsocaudal abdo-men, in the ventrocaudal abdomen ventral to therectum, caudal to the left kidney, and within thespleen). A number of these horses had a moderateincrease in the amount of peritoneal fluid imaged.26

Thickening of the small intestine or dilated smallintestinal loops may also be imaged. Large and/orsmall intestine may be adhered to the wall of theabscess and its motion restricted. Serial ultrasono-graphic evaluation was also useful to monitor thehorse’s response to treatment.26 Occasionally,mesenteric abscessation can also occur with Coryne-bacterium pseudotuberculosis.27

PeritonitisThe detection of an increased amount of hypoechoicor echogenic, flocculent, composite fluid, fibrin,and/or adhesions between the serosal surfaces of theintestine and the abdominal wall is compatible withperitonitis (Fig. 16). The abdomen and associatedgastrointestinal and abdominal viscera should bethoroughly scanned for the source of the peritonitissuch as an abdominal abscess or devitalized area ofbowel. The appearance of the peritoneal fluid in

Fig. 14. Sonogram of the left ventral abdomen in a horse withhemangiosarcoma involving the jejunum. Notice the markedthickening of the bowel wall and the anechoic to hypoechoic fluidcollection (arrows) and the loss of the normal bowel wall layering.

Fig. 15. Transrectal sonogram of a large mass in the mesenteryof a horse with an abdominal abscess. Notice the hypoechoicfluid filled abscess (arrows) and the hyperechoic echoes consistentwith gas within the fluid.

Fig. 16. Sonogram of the right side of the abdomen in the 13th

intercostal space obtained from a horse with peritonitis. Noticethe loculated fluid and hypoechoic fibrin (arrows) between theliver, right dorsal colon (RDC) and duodenum (D).



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horses with underlying gastrointestinal disease maybe more echoic and contain fibrin when comparedwith the peritoneal fluid in horses with Actinobacil-lus equuli peritonitis. Uroperitoneum should alsobe considered in horses with large anechoic perito-neal effusions. Free gas echoes and/or particulateechogenic debris are consistent with a ruptured vis-cus. Homogeneous, hypoechoic to echogenic cellu-lar fluid is imaged with hemoperitoneum, which isusually distinguished from septic fluid by the detec-tion of swirling fluid, associated with movement ofthe gastrointestinal viscera and respiration and thesettling and stirring of blood components (Fig. 17).The kidneys, liver, and spleen should be carefullyexamined in adults with hemoperitoneum to deter-mine if these organs are the cause of the hemor-

rhage. Uterine artery rupture is also a commoncause of hemoperitoneum in broodmares.

Peritoneal NeoplasiaCarcinomatosis appears as multiple hypoechoic toechoic homogeneous or heterogeneous masses thatline the peritoneal cavity and involve the mesenteryas well as metastasizing to other abdominal organsand lymph nodes. Hemoperitoneum is often seenin horses with carcinomatosis and was reported in35% of horses with hemoperitoneum.28 The perito-neal mesotheliomas also often have a homogeneoussonographic appearance with multiple masses lin-ing the peritoneal surfaces (Fig. 18).

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Fig. 18. Sonogram of the ventral abdomen in a mule with peri-toneal mesothelioma. Notice the anechoic to hypoechoic massinvolving the peritoneum and the large volume of anechoic tohypoechoic fluid in the peritoneal cavity.

Fig. 17. Sonogram of the left caudal ventral abdomen in a horsewith hemoperitoneum. Notice the echoic swirling fluid and thehypoechoic clot (arrow) lying along the ventral surface of theabdominal cavity.



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18. Edwards GB, Kelly DF, Proudman CJ. Segmental eosino-philic colitis: a review of 22 cases. Equine Vet J Suppl2000;32:86–93.

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24. Taylor SD, Haldorson GJ, Vaughan B, et al. Gastric neopla-sia in horses. J Vet Intern Med 2009;23:1097–1102.

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26. Pusterla N, Whitcomb MB, Wilson WD. Internal abdominalabscesses caused by Streptococcus equi subspecies equi in 10horses in California between 1989 and 2004. Vet Rec 2007;160:589–592.

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