Use of Thoracic Ultrasonography in the Ambulatory and ...the transducer cranially across the thorax...

Use of Thoracic Ultrasonography in theAmbulatory and Referral Setting

Virginia B. Reef, DVM

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

1. Introduction

Thoracic ultrasonography is a widely used diagnostictechnique for the evaluation of equine thoracic dis-eases in both the ambulatory and referral settings,yielding information about the lung and pleural cavitythat can be attained noninvasively and stallside.1,2

The side(s) of the thorax affected, as well as the preciselocation of lesions, can be determined in most horsesbecause the involved lung segment is usually pleural-based (exceptions are lesions located in the axial por-tion of the lung with no peripheral lung involvement ora hernia in the axial portion of the diaphragm with nogastrointestinal viscera against the thoracic wall ordorsal displacement of the peripheral lung). Thecharacter of pleural fluid can be determined ultrasono-graphically, as can the type and severity of many typesof pulmonary parenchymal disease. The cranial me-diastinum can also be evaluated ultrasonographically.

2. Examination Technique

Ideally, the hair over the portion of the thorax underexamination should be removed with a No. 40 sur-gical clipper blade. The size of the clipped areashould initially be based on the auscultatory find-ings and enlarged as needed to include the entireabnormal lung. In many horses with fine haircoats, an adequate image can be obtained by spray-

ing and saturating the hair and underlying skinwith alcohol or cleaning the hair and skin and thenapplying an ultrasound coupling gel in the directionof hair growth.

In a normal horse, the lung can be imaged on bothsides of the thorax from just below the dorsal para-spinous musculature to the ventral part of the tho-rax where the lung crosses the diaphragm. Theinitial scanning of the thorax should be performedwith the highest frequency transducer that pene-trates to the area of interest to obtain the best imagequality. A 7.5- to 15.0-MHz tendon transducer anda depth setting of 5 to 6 cm and a 6.0- to 10.0-MHzmicroconvex transducer and a depth setting of 6 to10 cm are both good for scanning the thorax of foalsand horses with superficial pathology. If extensivepulmonary or pleural disease is detected in an adulthorse or the horse is obese, a lower-frequency trans-ducer (5.0, 3.5 or 2.5 MHz) and/or an increased dis-played depth (25 to 30 cm in adult horses withsevere pleural or pulmonary disease) may be neededto penetrate and successfully image the abnormalityin its entirety. The scan should proceed slowly in adorsal to ventral direction in each intercostal space(ICS) with the transducer held parallel to the ribs sothat an entire respiratory cycle is imaged beforemoving ventrally to a different area. The right api-

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IN-DEPTH: ULTRASOUND OF THE THORAX AND ABDOMEN

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cal lung lobe and cranial mediastinum are imagedby placing the transducer in the right 3rd ICS justabove the level of the point of the elbow and anglingthe transducer cranially across the thorax towardsthe point of the left shoulder.1,2 The cranial medi-astinum can also be imaged by placing a low fre-quency transducer over the triceps in the 3rd ICSand scanning through the musculature into the cra-nial portion of the thorax.

3. Normal Structures

There is a large difference between the acoustic im-pedance of air and soft tissue resulting in air beinga near perfect reflector of ultrasound. Therefore,the normal visceral pleural surface of the lungappears as a straight hyperechoic line with charac-teristic equidistant reverberation air artifacts indi-

cating normal aeration of the pulmonary periphery(Fig. 1). Watching the lung as the horse breathes,the visceral pleural surface of the lung is imagedgliding over the diaphragm and moves ventrallywith inhalation and dorsally with exhalation, “thegliding sign.”1,2 In most normal horses there is nopleural fluid visualized, although small accumula-tions (up to 3.5 cm) of anechoic pleural fluid in themost ventral portions of the thorax have been de-tected in clinically normal horses. The diaphragmis curvilinear and appears thick and muscular in themore ventral locations and thin and tendinous dor-sally and caudally. The lung covers the cranial andcaudal mediastinum in most horses, although a hy-poechoic soft tissue mass (thymus) may be visual-ized in young horses in the cranial mediastinum.

4. Pleural Abnormalities

Pleural EffusionPleural effusion appears as an anechoic to hy-poechoic space between the lung, thoracic wall, dia-phragm, and heart. This fluid is usually found inthe most ventral portion of the thorax and causescompression of normal healthy lung parenchyma(compression atelectasis), retraction of the lung to-ward the pulmonary hilus, and a ventral lung tipthat floats in the surrounding fluid (Fig. 2).1,2 Thelarger the effusion, the greater the amount of com-pression atelectasis and lung retraction that occurs.With pleural effusions, the pericardial-diaphrag-matic ligament, a normal pleural reflection of theparietal pleura over the diaphragm and heart, isimaged as a thick membrane floating in pleuralfluid.1,2 This membrane runs from the thoracicside of the diaphragm over the heart and appears asa 3- to 6-mm thick, undulating sheet of homoge-neous tissue (Fig. 3). The thick band of echogenictissue that divides the cranial mediastinum intoright and left sides is also visible in horses with

Fig. 1. Sonogram of the lung in the left side of the thorax in the11th intercostal space obtained from a normal horse. Notice thehyperechoic line at the visceral pleural surface of the lung (arrow)casting the multiple reverberation artifacts. L, lung; IM, inter-costal musculature.

Fig. 2. Sonogram of the ventral aspect of the leftside of the thorax in the 8th intercostal space ob-tained from a horse with pleuropneumonia. No-tice the compression of the ventral tip of the lung(large arrow) by the surrounding hypoechoicfluid. The hypoechoic pleural fluid was visible inthe ventral thorax up to a line level with the pointof the shoulder (POS). This atelectic lung is com-pletely devoid of any air echoes. The lung (L)immediately dorsal to the area of compression at-electasis is more normally aerated with only a fewcomet tail artifacts (small arrow) imaged at thejunction between the more normally aerated dor-sal lung and the ventral compression atelecta-sis. D indicates diaphragm; S, spleen; LL, leftliver lobe; IM, intercostal musculature.

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pleural effusion due to the cranioventral fluid accu-mulation and the dorsally displaced lung.

Pleural Fluid CharacterThe sonographic pattern of pleural effusions in-cludes anechoic, complex nonseptated, and complexseptated fluid.1,2 Composite fluids are complex andmore echogenic than normal, containing fibrin, cel-lular debris, a higher cell count and total proteinconcentration, and gas. Anechoic sonolucent fluidrepresents a transudate or modified transudate witha relatively low cell count and total protein concen-tration. Increased echogenicity of the fluid indi-cates an increased cell count or total proteinconcentration (Figs. 2 and 3). A more heteroge-neous fluid with layering is more likely to occur withpyothorax. Blood within the pleural cavity (hemo-thorax) or within any body cavity often appearsmore homogeneous, with a hypoechoic to echogenicswirling pattern (Fig. 4). The fluid in a hemothoraxmay be septated and clots may be detected as soft,echogenic masses in the ventral aspect of the pleuralcavity.

Fibrin has a filmy to filamentous or frond-likeappearance and is usually hypoechoic.1,2 Fibrin isdeposited in layers or in web-like filamentousstrands on the parietal and visceral pleural sur-faces. Fibrinous loculations between the parietaland visceral pleural surfaces of the lung, diaphragm,pericardium, and inner thoracic wall limit pleuralfluid drainage (Fig. 5). As these fibrin strands be-come more organized and fibrous, they become morerigid and echogenic, often distorting the structuresto which they are attached during one phase of res-

piration and possibly restricting pulmonary me-chanics. This fibrin may eventually organize in thecranial mediastinum and wall this area off from therest of the thorax, resulting in a cranial mediastinalabscess (Fig. 6).

The cells and cellular debris in pyothorax aremore echogenic, heavier, and in the most ventrallocation, whereas the less cellular fluid or gas cap isdetected dorsally. Free gas within the fluid (poly-

Fig. 3. Sonogram of the ventral aspect of the left side of thethorax in the 7th intercostal space obtained from a horse withpleuropneumonia. Notice the echoic membrane (large arrows)overlying the diaphragm (D) floating in the hypoechoic fluid,which is the normal pericardiodiaphragmatic ligament. Theventral lung, although somewhat collapsed, still has small hyper-echoic linear echoes representing free gas within the lung. Atthe interface between the dorsal more normally aerated lung (L)and the ventral partially collapsed lung are several comet tailartifacts (small arrows). IM indicates intercostal musculature.

Fig. 4. Sonogram of the ventral aspect of the left side of thethorax in the 9th intercostal space obtained from a horse withhemothorax. Notice the echoic swirling fluid (large arrow) in theventral thorax consistent with blood. The blood was visible inthe ventral thorax up to a line level with the point of the shoulder(POS). There are several comet tail artifacts (small arrows) inthe ventral portion of the lung (L) emanating from small areas inthe lung parenchyma that are not normally aerated. D indicatesdiaphragm; S, spleen; IM, intercostal musculature.

Fig. 5. Sonogram of the ventral aspect of the left side of thethorax in the 9th intercostal space obtained from a horse withfibrinous pleuropneumonia. Notice the lacey network of hy-poechoic to echoic fibrinous loculations (small arrows). The ven-tral tip of the left lung (L) is atelectic (large arrow), compressed bythe surrounding hypoechoic fluid. The fibrinous loculations andhypoechoic pleural effusion was imaged up to a line located 12 cmproximal to the point of the shoulder (PPOS). D indicates dia-phragm; S, spleen; IM, intercostal musculature.



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microbullous fluid) is imaged as small, very brighthyperechoic echoes within pleural fluid with morefree gas echoes imaged dorsally in the pleural fluid(Fig. 7).1–3 The echoes from the microbubbles areusually pinpoint and linear. The mixing of air orgas microbubbles and pleural fluid causes polymi-crobullous fluid.3 The microbubble echoes moverapidly and spontaneously in various directions, de-pending on respiratory, cardiac, and the horse’smovements. The free gas echoes often adhere tothe fibrinous pleural surfaces and may be detectedhere initially without being mixed into the pleuralfluid.1,2 Free gas echoes may also be compartmen-talized in only one portion of the thorax when ini-tially imaged but usually spread rapidly to allportions of the thorax. Free gas echoes are usuallycaused by an anaerobic infection within the pleuralcavity.1,2 Free gas echoes were detected in thepleural or abscess fluid of 74% of horses with con-firmed anaerobic pneumonia.3

Hemothorax secondary to thoracic trauma is occa-sionally seen in the adult horse. The ribs should becarefully evaluated ultrasonographically for frac-tures because sonographic diagnosis of rib fracturesis superior to radiographic diagnosis. The lungsshould be carefully evaluated for any evidence ofpulmonary contusion, the thorax should be carefullyevaluated for a pneumothorax, and the diaphragmshould be examined sonographically for any evi-dence of a diaphragmatic hernia. Myocardial con-

tusion has also been seen in the adult horsesecondary to rib fractures.

Hemangiosarcoma should always be considered inthe differential diagnosis of hemothorax in adulthorses because this is one of the more common thoracicneoplasms in horses. Multiple pleural and subpleu-ral masses (Fig. 8) are often imaged that vary in size,and involvement of the adjacent intercostal or dia-phragmatic musculature may be present. In a studyof 35 horses with disseminated hemangiosarcoma,79% had involvement of the lung and pleura.4 Largevolumes of blood were present in the pleural cavity in20% of the 35 horses.4 Hemothorax has also beendetected ultrasonographically in the thorax of horsesafter a lung biopsy.5 Intense exercise in one horsewas associated with the development of hemothoraxand pneumothorax.6

PneumothoraxA gas-fluid interface is detected in horses with hy-dropneumothorax (pleural effusion and pneumotho-rax) (Fig. 9).1,2 Pneumothorax is usually secondaryto pleuropneumonia or to thoracic trauma and maybe bilateral (19/40 cases) or unilateral (17/40 cases).7

A pneumothorax caused by severe consolidation,pulmonary parenchymal necrosis, and/or a bronchi-al-pleural fistula is more frequently unilateral(64.7% of 40 horses).7 The gas-fluid interface canbe imaged moving simultaneously in a dorsal toventral direction with respiration, the “curtain

Fig. 6. Sonogram of the ventral aspect of the cranial mediasti-num in the right 3rd intercostal space obtained from a horse withfibrinous pleuropneumonia with a developing cranial mediastinalabscess (arrows). Notice the hypoechoic to echoic loculated fi-brin and hypoechoic fluid that is organizing into an oval, thick-walled abscess. The mediastinal septum (MS) is imageddividing the right and left sides of the mediastinum. A smallamount of more anechoic fluid is imaged in the left side of thecranial mediastinum.

Fig. 7. Sonogram of the ventral aspect of the left side of thethorax in the 7th intercostal space obtained from a horse withanaerobic pleuropneumonia. Notice the bright hyperechoicechoes in the pleural fluid consistent with polymicrobullous fluid(large arrows) surrounding the consolidated lung (CL). The vis-ceral pleural surface of the left lung (small arrows) is hyperechoicdue to the presence of gas stuck on the visceral pleural surface ofthe lung. The ventral lung is somewhat compressed by the largeamount of polymicrobullous fluid that surrounds it but is notcompletely collapsed; the axial lung is bulging and hypoechoic,consistent with parenchymal consolidation. L indicates lung;IM, intercostal musculature.



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sign,” reproducing the movements of the dia-phragm.1,2 The deeper lung echo changes positionrelative to the pleural fluid, whereas the dorsal freegas echo moves with pleural fluid movement andrespiration. The lung is imaged floating in thepleural fluid and retracted toward the pulmonaryhilus. A pneumothorax without pleural effusion ismore difficult to detect ultrasonographically becausefree gas in the pleural cavity and air within the lungperiphery have the characteristic hyperechoic reflec-

tion and regular reverberation artifacts and are bothlocated immediately adjacent to the parietal pleura.To detect dorsal pneumothorax in horses withoutpleural effusion, the scan should begin at the mostdorsal aspect of the thorax and continue ventrally,looking for a break in the characteristic reverbera-tion air artifact.1,2 A soft tissue density echo maybe detected at the site of pulmonary atelectasis be-tween the dorsal free gas echo and the ventral airecho from the aerated lung.

Noneffusive PleuritisA dry pleuritis is more difficult to detect ultrasono-graphically because there is no fluid separating pa-rietal and visceral pleural surfaces. Carefulexamination of the interface between the parietaland visceral pleural surfaces should be performedduring inspiration and expiration, evaluating move-ment of the visceral pleural lung surface relative tothe parietal pleural surface of the thoracic wall anddiaphragm. If movement of the lung across theparietal pleural surfaces is rough or erratic, a drypleuritis is probably present. Absence of any move-ment between these surfaces during respiration isalso an indication of a dry pleuritis or adhesionsbetween parietal and visceral pleural surfaces but isoccasionally seen in normal horses taking very shal-low breaths.1,2

5. Pulmonary Abnormalities

Compression AtelectasisCompression atelectasis occurs whenever the lungparenchyma is collapsed by fluid, air, or viscera inhorses with diaphragmatic hernia. The com-pressed lung is collapsed (see Figs. 2, 3, 5, and 9) andsmaller airways are no longer aerated, leaving thisportion of lung hypoechoic (echogenicity of soft tis-sue). The atelectic lung is retracted toward thehilus. Linear air echoes may be imaged in largerairways and appear crowded together as they con-verge toward the root of the lung. Normal lung isalso lighter than fluid and floats on top of and withinpleural fluid.

ConsolidationThe earliest sign of consolidation may be dimpling oran irregularity of the visceral pleural surface of thelung, a nonspecific change caused by nonuniformaeration of the lung periphery. Comet-tail artifactsradiate from these nonaerated areas. In horseswith pneumonia, sonolucent areas representingpulmonary parenchymal consolidation appear,surrounded by normally aerated portions of lung.These areas of pulmonary parenchymal consolida-tion usually have an irregular margin with hyper-echoic artifacts deep to the lesion. Smallconsolidated areas may be imaged only during ex-halation because the lesion moves underneath theadjacent rib or inhaled air entering the surroundingairways and alveoli intervenes, reflecting the ultra-

Fig. 8. Sonogram of the ventral aspect of the left side of thethorax in the 10th intercostal space obtained from a horse withhemothorax and hemangiosarcoma. Notice the subpleuralechoic mass on the diaphragm (D) and the adjacent hypoechoicfluid which was swirling in real time, consistent with blood. Thepericardiodiaphragmatic ligament (small arrows) is also visi-ble. IM indicates intercostal musculature.

Fig. 9. Sonogram of the ventral aspect of the right side of thethorax in the right 13th intercostal space obtained from a horsewith a necrotizing pleuropneumonia and a hydropneumotho-rax. Notice the air fluid interface (large arrow) adjacent to theparietal pleural surface and the lung (L) located much deeper inthe thorax surrounded by hypoechoic pleural fluid. There is asmall amount of hypoechoic fibrin (small arrows) on the visceralpleural surface of the lung. The ventral lung is compressed bythe surrounding fluid. D indicates diaphragm; RL, right lobe ofthe liver; IM, intercostal musculature.



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sound beam and preventing their visualization.Peripheral lung irregularities and lung consolida-tion occur in horses with equine influenza virus in-fection.8,9 The ultrasonographic diagnosis ofpulmonary parenchymal consolidation is based onthe detection of sonolucent pulmonary parenchymaand visualization of one or more of the lung’s ana-tomical features: sonographic air bronchograms,sonographic fluid bronchograms, pulmonary vessels,or scattered echogenic foci due to residual air inconsolidated lung parenchyma.1,2

Sonographic air bronchograms are imaged as dis-tinctive hyperechoic linear air echoes in sonolucentlung (Fig. 10).1,2 These hyperechoic linear echoescorrespond to the traditional air bronchograms de-tected on thoracic radiographs. These stronglyechogenic branching lines of the air-filled bronchiconverge towards the root of the lung, becominglarger as they merge. Sonographic fluid broncho-grams are nonpulsatile, anechoic tubular structuresthat also converge toward the root of the lung, be-coming larger as they converge (Fig. 11).1,2 In con-trast to air bronchograms, fluid bronchograms areonly detectable sonographically, not radiographi-cally. Although the diameter of sonographic fluidbronchograms normally decreases toward the super-ficial fluid alveologram, an increase in its diametertoward the periphery suggests pulmonary consolida-tion with bronchiectasis. Sonographic fluid bron-chograms can be differentiated from pulmonaryvessels that are pulsatile, tubular structures thatalso enlarge as they converge toward the root of thelung.

Consolidation areas are usually located cranioven-trally with the right lung more frequently and more

severely affected. Often, if the ultrasound examina-tion is performed very early in the course of the diseaseand the pneumonia is severe, it will appear less exten-sive. These small sonolucent “tip of the iceberg” ar-eas tend to coalesce into larger areas of consolidationas the disease process continues. A large area of con-solidated lung is usually wedge-shaped, poorly de-fined, and sonolucent. Large areas of consolidationoften appear heterogeneous (anechoic, hypoechoic, andhyperechoic) sonographically. Hepatization of lungparenchyma occurs with severe consolidation, result-ing in an ultrasonographic appearance similar toliver.1,2,10 Multiple small hyperechoic gas echoes in aseverely consolidated or hepatized lung are suggestiveof an anaerobic pneumonia.1,2 A rounded or bulgingarea of consolidation suggests severe consolidation,often progressing to pulmonary necrosis or abscessformation.

Parenchymal Necrosis

A gelatinous-appearing lung occurs with parenchy-mal necrosis; the affected lung is usually sonolucentand bulging, although collapse of this area may fol-low (Fig. 12).1,2 These necrotic areas then both cav-itate and form an abscess or rupture into the pleuralspace creating a bronchial-pleural fistula. Pulmo-nary infarcts should be suspected when a clearlydemarcated hypoechoic to echoic area of lung is im-aged. The infarcted area often appears more echoicthan the adjacent consolidated lung and has a seg-mental appearance. Color flow and power Dopplerultrasound can be used to evaluate pulmonary bloodflow in suspected areas of infarction.

Fig. 10. Sonogram of the ventral aspect of the right side of thethorax in the 6th intercostal space obtained from a horse withpleuropneumonia. Notice the large, wedge-shaped hypoechoicconsolidated ventral lung with the hyperechoic tubular struc-tures (arrows) containing air consistent with air broncho-grams. The consolidated ventral lung is surrounded byhypoechoic pleural fluid, and the more dorsal lung (L) containsair. D indicates diaphragm; IM, intercostal musculature.

Fig. 11. Sonogram of the ventral aspect of the right side of thethorax in the 6th intercostal space obtained from a horse withpleuropneumonia. Notice the severe consolidation of the rightlung (L) and the fluid bronchograms in the center of the hepatizedventral lung. There is a small amount of hypoechoic pleuralfluid that surrounds the wedge-shaped consolidated lung. Thereare several small bronchi within the ventral consolidated lungthat still contain air (small arrows). IM indicates intercostalmusculature.



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Pulmonary ThromboembolismPulmonary thromboembolism should be suspectedwhen the horse presents with respiratory distressand tachycardia. Risk factors for the developmentof pulmonary thromboembolism are intravenouscatheterization, extrapulmonary thrombophlebitis,and a hypercoagulable state. The sonogram of thelungs reveals large hypoechoic areas of consolidationand/or echoic segmental areas consistent with pul-monary infarction. Echocardiographic examina-tion reveals severe dilation of the pulmonary artery,right ventricle, and right atrium, with associatedpulmonic and tricuspid regurgitation in the absenceof any primary cardiac disease. Severe dilation ofthe pulmonary artery also occurs in horses withpulmonary hypertension.

Bronchial Pleural Fistula/AbscessA bronchial-pleural fistula is diagnosed ultrasono-graphically when the visceral pleural edge of thelung is no longer present, a cavitation is imagedinvolving the visceral edge of the lung, and hyper-echoic air echoes and sonolucent fluid echoes can beimaged in real time moving from the gelatinous areaof pulmonary necrosis into the pleural space.1,2

This results in a pneumothorax, as a bronchus com-municates with the pleural space. The pneumotho-rax may occur with or without a concomitant pleuraleffusion. Horses with bronchial-pleural fistulas, ifthey survive, usually develop a large bronchial-pleu-ral abscess surrounding the site of the bronchial-pleural fistula (Fig. 13).

Pulmonary AbscessAbscesses are identified ultrasonographically in thelung by their cavitated appearance and the absence

Fig. 12. Sonogram and postmortem specimen of the right lung of a horse with severe necrotizing pneumonia and abscessation. A,Sonogram of the right side of the thorax in the 6th intercostal space. Notice the large axially located anechoic area in the lungparenchyma (large arrows), consistent with an area of necrosis and the hypoechoic hepatized consolidated ventral lung. There is alsoa layer of hypoechoic fibrin (small arrows) overlying the visceral pleural surface of the lung. D indicates diaphragm; L, lung. B,Postmortem specimen of the right lung showing the necrotic area in the axial portion of the lung surrounded by consolidation. Thelung is covered with organized fibrin. The necropsy was performed several weeks after the sonogram was obtained. The necroticarea is better defined, and the layer of superficial fibrin is thicker.

Fig. 13. Sonogram of the right side of the thorax in the 10th

intercostal space obtained from a horse with a bronchopleuralabscess. Notice the dorsal gas cap (large arrow) and the ventralpolymicrobullous fluid within the abscess. The abscess has athick echoic capsule (small arrows). The more normal dorsallung (L) is immediately adjacent to the parietal pleura, fixed inposition by the thick abscess capsule. On the axial side of theabscess capsule is the diaphragm, the lung is on the dorsal side,the parietal pleura is superficial of the abscess, and the ventralangle of the pleural cavity is on the ventral side of the abscess.



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of any normal pulmonary structures (vessels orbronchi) detected within (Fig. 14).1,2 An anechoicarea lacking air or fluid bronchograms with acousticenhancement of the wall or lung deep to the sonolu-cent area is the initial sonographic appearance of anabscess. Abscesses may be encapsulated with anechogenic fibrous capsule but are more frequentlyimaged without any ultrasonographic evidence ofencapsulation. The material contained within theabscess may vary from anechoic to hyperechoic, de-pending on the type of exudate present. Locula-tions or compartmentalization of the abscess may bepresent. Most abscesses are more sonolucent thanthe surrounding pulmonary parenchyma but mayappear more echogenic if thick purulent or caseousexudate is present.

Hyperechoic free gas echoes may be imaged mixedin with the exudate, again suggesting the presenceof anaerobic organisms. The material within theabscess tends to be layered with the heaviest, mostechogenic debris in the most ventral portion of theabscess, followed by more sonolucent fluid in thecenter, with the hyperechoic gas echoes in the mostdorsal portion of the abscess (Fig. 15). The detec-tion of a dorsal gas cap within the abscess is indic-ative of a bronchial communication and probableanaerobic infection.

Fungal PneumoniaThe sonographic findings in horses with fungal pneu-monia reveal irregular hypoechoic areas of parenchy-mal consolidation that are scattered throughout thelung. Coalescing areas of parenchymal consolidationare often seen. Although the ultrasonographic find-ings in horses with fungal pneumonia appear similaron cursory examination to those in horses with diffuse

granulomatous disease, metastatic neoplasia, or pul-monary fibrosis, closer examination with high-resolu-tion transducers usually reveals the persistence ofairways and vessels in much of the affected lung tis-sue. In contrast, the pulmonary architecture is usu-ally disrupted in horses with diffuse granulomatousdisease, metastatic neoplasia, or pulmonary fibrosisand is replaced by granulomas, areas of neoplasticinfiltration, or infiltrating fibrous tissue, respectively.

Pulmonary Neoplasia/GranulomatousDisease/Pulmonary FibrosisThe detection of small multifocal sonolucent to echo-genic masses distributed randomly throughout thelung is consistent with granulomatous disease, fun-gal pneumonia, or metastatic neoplasia and rarelywith primary pulmonary neoplasia or equine multi-nodular pulmonary fibrosis (Fig. 16).1,2,11 Thesesoft tissue masses are usually small and diffuselyscattered throughout the lung field. The majorityof neoplastic pulmonary masses are homogeneousand hypoechoic, compared with the surroundingnormal lung, but may be isoechoic or have heteroge-neous echogenicity. Neoplastic masses can usuallybe differentiated from parenchymal consolidation bythe absence of bronchial and normal vascular struc-tures within the masses. Cystic necrotic areas orareas of dystrophic calcification casting acousticshadows may be imaged within neoplastic masses.

6. Cranial Mediastinal Abnormalities

Pleural Effusion/Cranial Mediastinal AbscessPleural fluid accumulation is the most common ab-normality detected ultrasonographically in the cra-nial mediastinum. If a large amount of fluid is

Fig. 14. Sonogram of the right side of the thorax in the 6th

intercostal space obtained from a horse with a pulmonary ab-scess. Notice the anechoic cavitated abscess in the ventral lung(arrows) lacking any pulmonary architectural lung struc-tures. The ventral lung is hypoechoic and lacking any aerationconsistent with consolidation. D indicates diaphragm; L, lung;IM, intercostal musculature.

Fig. 15. Sonogram of the right side of the thorax in the 13th and14th intercostal spaces obtained from a horse with an anaerobicpulmonary abscess. Notice the hyperechoic gas echoes liningthe abscess (small arrows) and the dorsal gas cap (large arrow)visible in the right 14th intercostal space. The dorsal gas cap isobscured from view by the overlying aerated lung in the right 13th

intercostal space. L indicates lung; D, diaphragm; IM, intercos-tal musculature.



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present in the cranial mediastinum, the heart willbe pushed caudally one or two ICS. In thesehorses, the cranial mediastinum is also easily im-ageable from the left side of the thorax, using thesame ICS and scan plane as would be used on theright side of the thorax. With chronic complex effu-sions, the fluid in the cranial mediastinum may walloff and become encapsulated as an abscess, occasion-ally causing signs of cranial vena caval obstructionor creating a systolic murmur associated with rightventricular outflow tract obstruction.1,2,12,13

Cranial Mediastinal NeoplasiaSoft tissue masses may be imaged in the cranialmediastinum and are most common in horses withthoracic lymphosarcoma (Fig. 17) but may be de-tected in horses with mesothelioma or hemangiosar-coma. Other neoplasms such as melanomas mustalso be considered.14 Lymphosarcoma masses inthe cranial mediastinum are usually associated withlarge pleural effusions, making these large soft tis-sue masses easier to image. These masses usuallyoccupy the entire cranial mediastinum, obliteratingthe normal thick membranous division imaged inhorses with pleural effusion.1,2,15,16 The mass usu-ally displaces the right apical lung lobe dorsally, theheart caudally, and therefore can be imaged fromeither side of the thorax in the 3rd ICS. In mosthorses, only one large mass can be imaged that mayhave a homogeneous or heterogeneous ultrasono-graphic appearance. This mass may be imaged ex-tending dorsally and cranially toward the thoracic

inlet. Involvement of the ventral cervical lymphnodes may also be detected in horses with cranialmediastinal lymphosarcoma.

7. Diaphragmatic Hernias

Diaphragmatic hernias are likely to result in visceraoccupying a portion of the caudal mediastinum or cau-dal thorax. A diaphragmatic hernia can be diagnosedultrasonographically when viscera is imaged in thethoracic cavity immediately adjacent to the lung orfloating within pleural fluid without the diaphragmseparating the thoracic and abdominal viscera (Fig.18).1,2 The diaphragmatic hernia is more likely toinvolve the left side of the diaphragm.17

8. Patient Management and Prognosis

The thoracic ultrasound examination can be used tohelp form a more accurate prognosis for survival andselect appropriate diagnostics and treatment at thehorse’s initial presentation, as well as monitoringresponse to therapy.1,2 The findings on sono-graphic examination can be used to decide if thora-cocentesis is indicated and to select the mostproductive site for thoracocentesis. The thoracicultrasonographic examination can also be used todetermine when antimicrobial therapy can be dis-continued and to monitor the horse thereafter.

Most horses with solitary pulmonary abscesses havereturned successfully to racing after treatment.18

The majority of Thoroughbred horses with pleuro-pneumonia were able to race at least once aftersuccessful treatment of pleuropneumonia.19 The

Fig. 16. Sonogram of the right lung (L) in the right 13th inter-costal space obtained from a horse with multinodular pulmonaryfibrosis. Notice the variable-sized hypoechoic areas in the pul-monary periphery (arrows). IM indicates intercostal muscula-ture.

Fig. 17. Sonogram of the right side of the thorax in the 3rd

intercostal space obtained from a horse with cranial mediastinallymphosarcoma. Notice the large multilobular hypoechoic toheteroechoic mass in the ventral portion of the cranial mediasti-num and the mediastinal septum (MS). There is also a hy-poechoic pleural effusion imaged dorsal to the masses. IMindicates intercostal musculature.



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prognosis for racing in these horses was worse forthose that developed a pulmonary abscess, cranial tho-racic mass, or a bronchial pleural fistula.19 Survivalof horses with pleuropneumonia is more likely if pleu-ral fluid, fibrin, loculations, free gas echoes, or paren-chymal necrosis are not detected on the initialultrasonographic examination.1,2 If free gas echoesare detected in pleural fluid, a guarded to grave prog-nosis should be given and broad spectrum antimicro-bial therapy, including coverage effective againstanaerobic microorganisms (metronidazole), should beinitiated immediately, even before results of cultureand sensitivity testing are available.1,2 The detectionof parenchymal necrosis also warrants a grave toguarded prognosis. Horses with parenchymal necro-sis should also be treated aggressively with broad-spectrum antimicrobials covering an anaerobicspectrum. If pulmonary infarction or thromboembo-lism is suspected, the affected area of the lung shouldbe examined with color flow and power Doppler ultra-sonography to determine if there is normal pulmonaryblood flow to the affected portion of the lung.

References1. Reef VB. Thoracic Ultrasonography: Noncardiac Imaging.

Equine Diagnostic Ultrasound. Philadelphia: WB Saun-ders; 1998:187–214.

2. Reef VB. Thoracic ultrasonography. Clin TechniquesEquine Pract 2004;3:284–293.

3. Reimer JM, Reef VB, Spencer PA. Ultrasonography as adiagnostic aid in horses with anaerobic bacterial pleuropneu-monia and/or pulmonary abscessation: 27 cases (1984–1986). J Am Vet Med Assoc 1989;194:278–282.

4. Southwood LL, Schott HC, Henry CJ, et al. Disseminatedhemangiosarcoma in the horse: 35 cases. J Vet Intern Med2000;14:105–109.

5. Venner M, Schmidbauer S, Drommer W, et al. Percutane-ous lung biopsy in the horse: comparison of two instrumentsand repeated biopsy in horses with induced acute interstitialpneumopathy. J Vet Intern Med 2006;20:968–973.

6. Perkins G, Ainsworth DM, Yeager A. Hemothorax in 2horses. J Vet Intern Med 1999;13:375–378.

7. Boy MG, Sweeney CR. Pneumothorax in horses: 40 cases(1980–1997). J Am Vet Med Assoc 2000;216:1955–1959.

8. Gross DK, Morley PS, Hinchcliff KW, et al. Pulmonary ul-trasonographic abnormalities associated with naturally oc-curring equine influenza virus infection in Standardbredracehorses. J Vet Intern Med 2004;18:718–727.

9. Gross DK, Hinchcliff KW, French PS, et al. Effect of mod-erate exercise on the severity of clinical signs associated withinfluenza virus infection in horses. Equine Vet J 1998;30:489–497.

10. Carr EA, Carlson GP, Wilson WD, et al. Acute hemorrhagicpulmonary infarction and necrotizing pneumonia in horses:21 cases (1967–1993). J Am Vet Med Assoc 1997;210:1774–1778.

11. Donaldson MT, Beech J, Ennulat D, et al. Interstitial pneu-monia and pulmonary fibrosis in a horse. Equine Vet J1998;30:173–175.

12. Byars TD, Dainis CM, Seltzer KL, et al. Cranial thoracicmasses in the horse: a sequel to pleuropneumonia. EquineVet J 1991;23:22–24.

13. Griffin R. Cranial mediastinal abscess secondary to pleuri-tis in a 3-year-old Thoroughbred. Equine Vet Educ 2002;14:286–289.

14. MacGillivray KC, Sweeney RW, Piero FD. Metastatic mel-anoma in horses. J Vet Intern Med 2002;16:452–456.

15. Garber JL, Reef VB, Reimer JM. Sonographic findings inhorses with mediastinal lymphosarcoma: 13 cases (1985–1992). J Am Vet Med Assoc 1994;205:1432–1436.

16. De Clercq D, van Loon G, Lefere L, et al. Ultrasound-guided biopsy as a diagnostic aid in three horses with acranial mediastinal lymphosarcoma. Vet Rec 2004;154:722–726.

17. Romero AE, Rodgerson DH. Diaphragmatic herniation inthe horse: 31 cases from 2001–2006. Can Vet J 2010;51:1247–1250.

18. Ainsworth DM, Erb HN, Eicker SW, et al. Effects of pul-monary abscesses on racing performance of horses treatedat referral veterinary medical teaching hospitals: 45cases (1985–1997). J Am Vet Med Assoc 2000;216:1282–1287.

19. Seltzer KL, Byars TD. Prognosis for return to racing afterrecovery from infectious pleuropneumonia in Thoroughbredracehorses: 70 cases (1984–1989). J Am Vet Med Assoc1996;208:1300–1301.

Fig. 18. Sonogram of the left side of the thorax obtained from ahorse with a diaphragmatic hernia. Notice the 3 loops of smallintestine with long mesentery, consistent with jejunum floatingin the thorax ventral to the lung (L) and dorsal to the diaphragm(D). IM indicates intercostal musculature; SI indicates smallintestine.





Use of Thoracic Ultrasonography in the Ambulatory and ...the transducer cranially across the thorax...

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Transcript of Use of Thoracic Ultrasonography in the Ambulatory and ...the transducer cranially across the thorax...