Ultrasound of the Thorax and Abdomen in the Foal - AAEP · Ultrasound of the Thorax and Abdomen in...

Ultrasound of the Thorax and Abdomen in the Foal

Fairfield T. Bain, DVM, MBA, Diplomate, ACVIM, ACVP, ACVECC

Ultrasonography in the neonate may be used in the initial evaluation to determine an anatomiclocation of sepsis or to evaluate for traumatic injury secondary to dystocia. It is often the firstdiagnostic tool applied after the physical evaluation of the foal. Author’s address: School of Vet-erinary Science, University of Queensland, Gatton, Queensland 4343, Australia; e-mail:[email protected]. © 2012 AAEP.

1. Introduction

Ultrasonography has become a routine part of med-ical examination of the foal and is a valuable tool foracquiring information on structural pathology of or-gans within the thorax and abdomen. In the neo-nate, it may be used in the initial evaluation todetermine an anatomic location of sepsis or to eval-uate for traumatic injury secondary to dystocia.Although we often separate disorders of the thoraxand abdomen into distinct categories, both body cav-ities are usually evaluated during the same ultra-sound examination. The ultrasound examinationis performed in a cranial-to-caudal manner—pass-ing the ultrasound probe along each intercostalspace, scanning from dorsal to ventral, and thensweeping the caudal and ventral abdomen behindand beneath the ribs.

2. Thoracic Ultrasound in the Foal

Disorders of the thorax in the neonatal foal includerib fractures, pneumonia, and effusions (septic,hemorrhagic, or other). Rib fractures are commonin hospitalized neonatal foals, and ultrasound isconsidered a more accurate method of detection com-pared with radiography and physical examina-tion.1,2 Fractures are most often located within 3

cm of the costochondral junction and more com-monly involve the first few ribs behind the elbow.Early on, a rib fracture may appear as a “green-stick” fracture (Fig. 1), detected on ultrasound asa slight discontinuity of the external cortical sur-face. Later, increasing displacement of the frac-ture site is detected sonographically as moreseparation of the fracture fragments with the dis-tal segment usually moving medially (Fig. 2).There may be fluid or hemorrhage in the soft tis-sues surrounding the fracture ends with multifo-cal echolucent areas (Fig. 3). Some indentation(or step deformation) of the parietal and visceralpleural surfaces may also be detected. Injury tothe underlying pulmonary parenchyma can varyfrom mild bruising with a few echogenic “comettails” to progressively more involvement with pa-renchymal consolidation and occasional hemotho-rax or pneumothorax. Serial evaluation of thedegree of displacement is recommended to deter-mine if there is risk of cardiac injury or progres-sive change in the lung— either might be anindication to consider surgical stabilization versusconservative management of restricted mobility inthe stall. Ultrasound can also be useful in mon-itoring the fracture healing process— determining

38 2012 � Vol. 58 � AAEP PROCEEDINGS

IN-DEPTH: ULTRASOUND OF THE THORAX AND ABDOMEN

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when there is sufficient callus formation and frac-ture stability to allow more exercise. With frac-ture of more caudal ribs, there may be injury tothe diaphragm and possible diaphragmatic herniawith intestinal structures within the pleural space(Fig. 4).

Ultrasound has become a routine tool in the eval-uation of pneumonia in the foal. Pneumonia can bea primary anatomic site of sepsis in the neonate.Early identification can be useful in determining theseverity of the disease process as well as monitoringthe response to medical therapy. Patterns ofchanges on the ultrasound image can be helpful inpredicting the type of lung injury present. Scat-tered echogenic “comet tails” (Fig. 5) may be presentin the early stages of a variety of bacterial pneumo-nias, with ventral consolidation (Fig. 6) being evi-dent with further progression or more seriouspneumonia. Broad-based or diffuse echogenic

shadowing is more consistent with interstitial lungdisease (pulmonary edema or interstitial pneumo-nia) and suggests a more serious disease process.Serial ultrasonographic examination of the lung isuseful in evaluating the progression of disease andcan be a component for evaluating response to med-ical therapy.

3. Abdominal Ultrasound in the Foal

Ultrasound examination of the abdomen of foals isoften used in the evaluation of foals with signs ofcolic and can be useful in differentiating causes ofabdominal distention in foals with and without colicsigns.3 While not the focus of this presentation,ultrasound is useful in evaluation of disorders of theumbilical structures and abnormalities of the ab-dominal wall surrounding the umbilicus and theinguinal area (e.g., traumatic injury acquired duringdelivery and congenital defects).

Fig. 1. “Greenstick,” or nondisplaced rib fracture.

Fig. 2. Displaced rib fracture. Note distal fragment (right) dis-placed medially.

Fig. 3. Multifocal echolucent areas adjacent to rib fracture in-dicating local soft tissue trauma and fluid accumulation.

Fig. 4. Ultrasound appearance of pleural effusion and presenceof intestinal structures in pleural space consistent with diaphrag-matic hernia. Long arrow indicates tip of lung; arrowhead, in-trathoracic intestine; short arrow, diaphragm. Dorsal is to theleft (image courtesy of Dr. Eric Mueller).

AAEP PROCEEDINGS � Vol. 58 � 2012 39


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The approach to the ultrasound examination ofthe foal with signs of acute abdominal pain is similarto that used for the adult equine patient. There aresome special circumstances and lesions that may beunique to the younger foal that must be evaluated.The use of a high-frequency (5 to 7.5 mHz or higher)probe—whether linear or microconvex—is sufficientfor imaging much of the abdominal cavity in theyoung foal with good resolution of structures. Thiscan be performed with the foal standing or in arecumbent position.

The ultrasound examination should proceed aswith the adult patient by evaluating the ventralthorax and abdomen by passing the ultrasoundprobe dorsal to ventral along each intercostal spacebeginning just caudal to the triceps muscle on eachside and progressing in a cranial to caudal fashion to

the thigh. The exam is completed by then sweepingthe ventral aspect of the abdomen to evaluate theumbilical structures and the urinary bladder.

4. Foals With Abdominal Pain and AbdominalDistension Can Have a Variety of Conditions

These conditions may include gas distension of thelarge colon in the foal with conditions such as meco-nium impaction or occasionally colonic tympany as-sociated with early rotavirus infection; smallintestinal fluid distension with small intestinal vol-vulus, or occasionally enteritis or intussusception;and peritoneal fluid accumulation with either uro-peritoneum, hemoperitoneum, or peritonitis.

Gastric distension (Fig. 7) can be evaluated in thefoal in a manner similar to that seen in the adult.Causes of gastric distension may include ileus withor without enteritis or small intestinal strangula-tion obstruction. Occasionally and usually in olderfoals, duodenal stricture (Fig. 8) associated with the

Fig. 5. Scattered echogenic “comet tails” associated with earlypneumonia.

Fig. 6. Ventral consolidation of lung parenchyma with bacterialpneumonia. Long arrow indicates consolidated lung tip; shortarrow, diaphragm. Dorsal is to the left.

Fig. 7. Fluid distension with milk clots (large arrowhead) of thestomach in a foal. Dorsal is to the right.

Fig. 8. Ultrasound image of thickened duodenum (arrow) con-sistent with duodenal ulcer disease and stricture. Dorsal is tothe right.



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gastroduodenal ulcer syndrome can be identifiedalong the right side of the abdomen; this is helpful inconfirming the need for surgical correction. Inthese patients, the amount of gastric distension maybe profound (Fig. 9)—possibly leading to gastric at-ony later in the course of the disease. Ultrasoundcan be useful in confirming the proper location of thenasogastric tube when attempting placement for en-teral feeding of a weak neonate or refluxing a foalwith colic (Fig. 10).

Small intestinal obstructive disorders such as vol-vulus or entrapment in scrotal hernias will appearsimilar to that seen in the adult patient—with pro-foundly fluid-distended segments of small intestineoccasionally with sedimentation of particulate ma-terial to the ventral or dependent aspect (Fig. 11).With the hernia, small intestinal segments may alsobe evident within the vaginal tunic.

Small intestinal disorders including enteritis canbe easily identified in the foal. The ultrasound

finding of fluid distension of the small intestinallumen along with variable motility and variablethickening (�2 to 3 mm) of the small intestinal wallconcurrent with fever and leucopenia is supportiveof the clinical diagnosis of enteritis (Fig. 12). Thesmall intestinal wall may often be less distinct withenteritis due to inflammatory cell infiltrates andvariable edema of the wall. In many geographicregions around North America, the ultrasound find-ing of a markedly thickened (�5 mm in some cases)small intestinal wall in older foals together with asyndrome of peripheral edema, hypoproteinemia,and hypoalbuminemia is considered consistent withLawsonia intracellularis infection (Figs. 13 and 14).Peripheral edema of the submandibular space aswell as edema of the ventral abdomen and distallimbs are usually consistent clinical signs; however,the presence of colic or diarrhea may be more vari-able. In some patients affected with Lawsonia,there will also be significant thickening of the largecolon wall due to mural edema (Fig. 15), presumablyassociated with the profound hypoproteinemia andhypoalbuminemia associated with this disease.

Fig. 9. Profound gastric distension associated with duodenalstricture in a foal.

Fig. 10. Acoustic shadow from nasogastric tube within lumen ofstomach.

Fig. 11. Distended nonmotile small intestine with sedimenta-tion of particulate matter associated with small intestinal volvu-lus.

Fig. 12. Ultrasound image of enteritis in the foal with indistinctintestinal wall.



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Additional diagnostics such as fecal polymerasechain reaction (PCR) and/or serology can be used toconfirm the diagnosis.

Colic associated with small intestinal obstructionfrom intussusceptions occur more commonly inyoung foals, often secondary to enteritis or dysmo-tility secondary to birth asphyxia. Serial ultra-sound examinations may be necessary to identifythe intussusception, which is classically described asa “target lesion” with the concentric rings of theintussuscepted intestinal wall (Figs. 16 and 17).

Occasionally, the acute onset of rotaviral enteritiswill result in variable signs of colic and inappetence,

sometimes before the appearance of diarrhea. Ab-dominal ultrasound can be useful in identifying liq-uid contents of both the small and large intestines,which may be indicative of impending diarrhea (Fig.18).

Foals with rib fractures will sometimes presentwith apparent colic signs. Diaphragmatic herniasassociated with rib fractures can occur due to lacer-ation of the diaphragm from rib fractures, or rarely,as a congenital diaphragmatic anomaly, and presentwith intrathoracic strangulation of the intestine.Other unusual findings in foals with colic may in-clude umbilical vascular disruption, internal organinjury associated with dystocia, and occasionally he-moabdomen of unknown origin.

The urogenital system of the foal represents aspecial system within the abdominal cavity of the

Fig. 13. Ultrasound image of small intestine from foal affectedwith Lawsonia intracellularis, showing marked thickening of thesmall intestinal wall. Double arrow indicates thickened mucosa;single arrow, serosa.

Fig. 14. Ultrasound image showing thickened small intestinewith Lawsonia intracellularis in a foal.

Fig. 15. Ultrasound image showing edema of the colon wall(arrows) associated with Lawsonia intracellularis in a foal.

Fig. 16. Cross-sectional ultrasound image of small intestinalintussusception.



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foal for ultrasound evaluation.4 Uroperitoneumsecondary to rupture of the urinary bladder is themost common abnormality (Fig. 19).5 Ultrasoundimaging usually demonstrates variable volumes ofvariably echogenic to hypoechoic peritoneal effusionwith free-floating intestinal organs. There aresome instances in which the peritoneal fluid associ-ated with uroperitoneum will appear quite echo-genic and require differentiation from suppurativeexudate associated with septic peritonitis by abdom-inocentesis. In cases of uroperitoneum associatedwith a ruptured urinary bladder, the bladder is usu-ally collapsed and folded on itself. The actual rup-ture site is usually located on the dorsal aspect of thebladder, although it may not be easily identified onthe ultrasound image. It is important to note thatruptures of the urinary tract may occur at sitesother than the urinary bladder, such as the urachusor ureters. Urachal ruptures often will have a pe-riumbilical plaque of edema associated with subcu-taneous leakage of urine. Ureteral ruptures resultin accumulation of urine in the retroperitoneal space

that may be imaged as hypoechoic fluid surroundingthe kidneys. Congenital defects of the kidneys andureters are occasionally seen. Hydroureter (Fig.20) can occur in neonates as a congenital conditionand can have a clinical presentation of neurologicsigns secondary to profound hyponatremia andpost–renal azotemia. Dilated tortuous ureters maybe seen as fluid-distended tortuous tubes exiting thekidney. Laboratory findings may demonstrateazotemia, hyponatremia, and hypochloridemia sim-ilar to that found with uroperitoneum.

5. Summary/Conclusions

Ultrasound imaging is a readily available diagnostictool that is easily applied to evaluation of the youngfoal, both in the hospital setting and in the field.In the author’s practice, it is often the first diagnos-tic tool applied after the physical evaluation of the

Fig. 17. Longitudinal ultrasound image of small intestinal in-tussusception.

Fig. 18. Ultrasound image of fluid distension of the large colonassociated with impending rotaviral diarrhea.

Fig. 19. Uroperitoneum with collapsed, ruptured urinary blad-der.

Fig. 20. Right kidney with hydroureter and dilated renal pelvis(thick arrow). Thin arrow indicates renal pelvis. Dorsal is tothe right.



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foal. In the absence of obvious abnormalities on thephysical evaluation, ultrasound provides an “on-the-scene” evaluation of changes in or on the organs ofthe thorax and abdomen of the foal that can directthe first steps in therapy, before obtaining results ofother diagnostics such as hematology or clinicalchemistry data. The time frame to reach a level ofcomfort and confidence for diagnostic ultrasonogra-phy of the foal is quite short. The thin body wall ofthe foal allows ease in observing body cavity struc-tures in excellent detail. A good first start is toevaluate normal foals in an effort to learn the pat-terns of sonographic appearance of normal internalorgans—learning parameters such as location,thickness, diameters, or a variety of structures.Scanning as many foals as possible, whether normalor abnormal, is certainly the best way to gain abroad level of experience in sonographic features.Sonographic findings will provide good support of

the physical examination findings and can some-times provide objective information that the practi-tioner can monitor over time to determine responseto therapy.

References1. Jean D, Picandet V, Maciera S, et al. Detection of rib

trauma in newborn foals in an equine critical care unit: acomparison of ultrasonography, radiography and physical ex-amination. Equine Vet J 2007;39:158–163.

2. Sprayberry KA, Bain FT, Seahorn TL, et al. Fifty-six cases ofrib fractures in neonatal foals hospitalized in a referral centerintensive care unit from 1997–2001, in Proceedings. Am As-soc Equine Pract 2001;47:395–399.

3. Reef VB. Pediatric abdominal ultrasonography. In Reef VB,editor. Equine Diagnostic Ultrasound. Philadelphia, PA:Saunders; 1998:364–403.

4. Hoffman KL, Wood AK, McCarthy PH. Ultrasonography ofthe equine neonatal kidney. Equine Vet J 2000;32:109–113.

5. Kablack KA, Embertson RM, Bernard WV, et al. Uroperito-neum in the hospitalized neonate: retrospective study of 31cases, 1988–1997. Equine Vet J 2000;32:505–508.





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