The Veterinary Journal

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Diagnostic ultrasonography in cattle with thoracic disease

M. Fl

ock

€

*

2nd Medical University Clinic for Ruminants and Swine, University of Veterinary Medicine, Veterinaerplatz 1, 1210 Vienna, Austria Accepted 3 June 2003

Abstract

The pleura and lungs were evaluated by means of sonography in 55 bovine patients with diseases of the thoracic cavity. For these ultrasound examinations, a range of transducers was used. As the lung surface was most often involved in cases of pulmonary disease, it was possible to detect ultrasonographically bronchopneumonia, consolidation, pleural effusion, pulmonary emphysema and pleuritis. Determination of the amount of lung tissue affected provided prognostic information. It was not possible to visualise lesions located deeper within the lungs where peripheral tissue was not affected. A diagnosis of thoracic disease was made on the basis of clinical and ultrasonographic findings and confirmed in 33 cases at necropsy.

Keywords:Sonography; Thorax; Respiratory disease; Traumatic reticuloperitonitis; Cattle

1. Introduction

The anatomical and physiological features of the re-spiratory system of cattle may predispose them to the development of pulmonary lesions much more fre-quently than other farm animal species. Cattle have a small physiological gaseous exchange capacity and greater resultant basal ventilatory activity predisposing them to low bronchiolar or alveolar oxygen levels dur-ing exposure to high altitudes and durdur-ing periods of active physical or metabolic activity. During these times, low oxygen tension or hypoxia may slow mucociliary and alveolar macrophage activity and decrease pul-monary clearance rates. The basal ventilatory activity is comparatively greater in cattle than in other mammals, resulting in the inspired air becoming progressively more contaminated with potentially infectious, allergenic, or noxious substances.

The bovine lung also has a higher degree of com-partmentalisation than other species and this predis-poses it to airway hypoxia peripheral to airways that become occluded, resulting in reduced phagocytic

ac-tivity and the retention or multiplication of infectious agents. Moreover, because of the low numbers of al-veolar macrophages in the bovine lung, the pulmonary clearance mechanism may not be as eﬀective as in other species. There is also a low level or atypical bioactivity of lysozyme in bovine respiratory mucus which may make cattle more susceptible to infection of the respiratory tract than other species (Radostits et al., 2000).

The severity of disease cannot always be determined by means of physical examination alone. Although physiological lung tissue cannot be examined, as ultra-sound waves are incapable of penetrating gas-ﬁlled structures, sonography is suitable for the detection of a number of pathological conditions within the thoracic cavity. Based on the sonographic appearance of the pulmonary surface and the ﬂuid in the pleural cavity, valuable prognostic information can be obtained and the healing process better followed (Braun, 1997; Reef, 1998; Reimer, 1990; Scott, 1998).

In the present study, ultrasound examinations were carried out in cattle with diseases of the thoracic cavity in order to determine the extent of the lesions and to assess better the prognosis. The results were compared with the ﬁndings determined following physical exami-nation and necropsy.

The Veterinary Journal 167 (2004) 272–280

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2. Materials and methods

All cattle (n¼55) with lung disease and/or suspected traumatic reticuloperitonitis (TRP) that were admitted to the 2nd Medical University Clinic for Ruminants and Swine, University of Veterinary Medicine, Vienna, be-tween 2000 and 2002, and on which thoracic ultraso-nography was performed, were included in this study. They were given a physical examination (Baumgartner, 1999), a haematological screen (Cellanalyzer CA 530, Medonic) and blood gas analysis (GEM Premier Plus, Instrumentation Laboratory) on the day of arrival.

Ultrasound examinations were performed using an Esaote AU5. In preparation, hair was clipped on both sides from a site caudal to the scapula to the last rib, and also from the transverse processes of the thoracic ver-tebrae to the elbow. The area was swabbed with alcohol to remove excess oil, and coupling gel (Arbo Ultrasound Gel Y05, Kendall) was applied. Examination of the pleura and lungs was carried out in the 7th to 11th in-tercostal spaces dorsoventrally parallel to the ribs. The heart was examined on both sides in the 3rd and 4th intercostal spaces halfway between the elbow and the shoulder (Braun, 1997; Braun et al., 2001).

In calves, a 7.5, 10, or 13 MHz linear transducer was used, but in older animals, a 3.5 and 5 MHz convex transducer was considered more suitable. For exami-nation of the heart in all animals, a sector transducer (2.5, 3.5, and 5 MHz) was selected. In cases of suspected TRP, ultrasonography of the abdomen was carried out on the ventral part of the thorax on both sides paras-ternally and along the left and right thoracic wall in the 6th and 7th intercostal spaces, using a 3.5 and 5 MHz convex transducer. The reticulum and its contractions, the ruminal atrium, the ventral sac of the rumen and the spleen were evaluated according to Braun (1997).

In incurable cases, patients were euthanased and sent for postmortem examination. The results of sonography were then compared with the findings of the physical examination and postmortem examination. A definitive diagnosis was established following necropsy in 33 cat-tle. In the 21 animals that did not go to necropsy, the diagnosis was reached on a clinical basis; they were treated with anitbiotics and anti-inflammatory agents, and after the end of the treatment they were returned to their owners. A sonographic examination was con-ducted only once in each patient.

3. Results

Nineteen calves and 36 young cattle and cows of the breeds Fleckvieh (n¼44); Schwarzbunte (n¼5) and Braunvieh (n¼6) were studied. There were 37 female and 18 male animals and the mean age was 3.0 years (range: 1 month to 11 years).

3.1. Clinical and haematological ﬁndings

Forty-three animals were admitted due to diseases of the lungs, 12 with suspected TRP. The animals with lung disease had a mean internal body temperature of 39.4°C (37.7–41.3 °C), a mean pulse of 96 per minute (72–120) and a mean respiratory rate of 48 per minute (20–90). Twenty-five exhibited mildly to moderately depressed behaviour, five animals showed coughing only upon stimulation, 23 had spontaneous coughing, and 29 suf-fered from dyspnoea. Upon auscultation of the lungs, eight cases exhibited mild to severe increased vesicular breath sounds, seven had rough breath sounds, 18 bronchial breath sounds, 27 rattling, splashing and pleuritic friction sounds, four had an absence of lung sounds and six cases of wheezing were detected. Some patients had a combination of these findings.

Upon percussion of the lungs, 40 animals exhibited reduced and three had increased resonance. Thirty-one patients had mild to severe raised muscle tone of the abdominal wall. The foreign body tests were positive in 15 animals. Patients with TRP had a mean internal body temperature of 39.5 °C (38.6–40.6°C), a mean pulse of 100 per minute (80–140) and a mean respiratory rate of 40 per minute (24–60). Four animals exhibited mild to moderate depressed behaviour, two displayed sponta-neous coughing, ﬁve had dyspnoea.

Upon auscultation of the lungs, there were four cases of mild to severe increased vesicular breath sounds, one case of bronchial breath sounds, two of rattling, splashing and pleuritic friction sounds and five had no lung sounds. Some patients had a combination of these findings. All patients with TRP exhibited reduced reso-nance upon percussion of the lungs, and one animal had increased resonance in the dorsal lung field. All of these animals had mild to severe raised muscle tone of the abdominal wall. The foreign body tests were positive in five patients.

In calves (less than six months old) with diseases of the lungs, erythrocytosis (x¼10:0,s¼1:71012/L) as well as an increase in CO2partial pressure (x¼60:9,s¼12:5 mmHg) and base excess (x¼7:9,s¼8:0 mmol/L) were determined. Adult animals exhibited lymphopenia (x¼45, s¼18:3%) and granulocytosis (x¼49, s¼ 19:1%) with mild leukocytosis; blood gases were within the normal range. In patients with TRP, leukocytosis (x¼10:4, s¼6:2109_/L), _{granulocytosis} ₍_x_¼_54, s¼15:3%) and lymphopenia (x¼42; s¼15:2%) were found. Blood gases were normal. Measures to identify the infectious agent were not attempted as all referred pa-tients had already been treated with antibiotics.

3.2. Sonography results in normal cattle

The ultrasonographic examination of the entire lung surface took about 15 min.

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3.2.1. Physiological appearance of the lungs and pleura Normal lung tissue could not be shown due to its air content but reverberation artifacts in the form of echo-genic bands running parallel to the surface of the lungs were visible (Fig. 1). Costal and pulmonary pleura could not always be distinguished and were represented by a smooth hyperechoic line between the surface of the lungs and the musculature of the thoracic wall (Fig. 1). The motion of the lungs synchronous with respiration was visible with both high frequency and low frequency transducers. In obese animals, reverberation artifacts were often not visible despite the presence of physio-logical lung tissue.

3.2.2. Physiological appearance of the abdomen

In healthy animals, the surface of the spleen, the wall of the reticulum, the ruminal atrium and the ventral ruminal sac were smooth and the reticulum exhibited biphasic contractions at regular intervals (one per min-ute) (Fig. 13).

3.3. Necropsy results

Thirty-four animals were euthanased, of which 33 were sent for necropsy. Eight animals exhibited ca-tarrhal-purulent pneumonia of the cranial lobes, five had catarrhal-purulent bronchopneumonia, one showed pneumonia with abscessation, two had puru-lent pneumonia of the cranial lobes, two fibrinous-purulent bronchopneumonia, three severe pulmonary emphysema, one septic pulmonary thrombi, one ate-lectasis, 12 pleuritis and pleural effusion, four aspiration pneumonia and nine TRP. Some individual patients had multiple findings.

3.4. Correlation between clinical examinations, sonogra-phy and necropsy results

Where pulmonary emphysema was diagnosed based on the physical examination (increased resonance and enlarged lung ﬁeld upon percussion, reduced vesicular breath sounds) numerous comet-tail artifacts in the form of bright, closely situated echo bands starting at the lung surface and running perpendicular to the pleura in the lung tissue were observed upon ultrasonography (Fig. 2). These comet-tail artifacts were found to be pulmonary emphysema at necropsy.

In cattle with clinical symptoms of bronchopneu-monia (pyrexia, nasal discharge, coughing, dyspnoea, increased vesicular to bronchial breath sounds, rattling and splashing sounds) disseminated round and wedge-shaped hypoechoic zones (from a few millimetres to several centimetres in size) with comet-tail artifacts were seen on the surface of the lung, in the cranio-ventral lung. These are particularly evident in the cranioventral lung ﬁelds as well as in individual areas of the dorsal lung, in otherwise physiologically normal lung tissue (Fig. 3). Predominantly in the cranioventral lobes, reduced resonance was detected on percussion of the chest. Within these areas, extensive hypoechoic zones resembling liver parenchyma without reverbera-tion artifacts were seen and were well demarcated from healthy tissue. Within the hypoechoic zones were dis-seminated hyperechoic and anechoic dot-shaped as well as some branched line-shaped structures (Figs. 4, 5 and 7) and also tubular structures with walls of varying echogenicity and ramiﬁcation towards the lung pe-riphery with hypoechoic to hyperechoic content (Fig. 6).

Fig. 1. Sonogram of the surface of a normal lung (5 MHz): echogenic line (P), visceral and parietal pleura, echogenic lines running parallel to the pulmonary surface (R), reverberation artifacts.

Fig. 2. Sonogram of pulmonary emphysema (5 MHz): the numerous echogenic bands (C) from the lung surface are comet-tail artifacts; (P), pleura.

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The round hypoechoic to anechoic zones on the surface of the lungs were found upon necropsy to be fluid-filled alveoli and consolidated lung lobules (Fig. 3). The extensive hypoechoic zones in the cra-nioventral lung fields and the cracra-nioventral portions of the main lobes turned out to be consolidated lung tis-sue, that were largely devoid of air as a result of

ate-lectasis caused by an obstruction (Figs. 4–6). Air-filled bronchi were seen as echogenic linear reflex bands with branches and acoustic shadowing or comet-tail artifacts (positive bronchogram, bronchoaerogram) or as lentil-shaped echos within the hypoechoic zones (caused by hyperaemia and exudation) (Figs. 4–6). Small, round anechoic zones were transverse sections of blood vessels (Fig. 5). The tubular structures with anechoic lumen Fig. 6. Sonogram of a lung of a calf with pneumonia of the cranial lobe (5 MHz): the lung tissue is hypoechoic in the cranial lung field and shows ramified fluid bronchograms (B), the hyperechoic echoes near the bronchial walls represent air inclusion; in real time mode, content of mixed echogenicity in the bronchi was visible, which moved syn-chronous to respiration, P, pleura.

Fig. 4. Sonogram of a lung of a calf with pneumonia of the cranial lobe (10 MHz): the normal lung tissue with reverberation artifacts on the left is distinctly delineated from the abnormal hypoechoic tissue with hyperechoic dot and line-shaped structures on the right (vertical arrow separating the areas); P, pleura.

Fig. 3. Sonogram of the lung of a cow with bronchopneumonia (5 MHz): the small hypoechoic zone on the surface of the lung (diameter: 0.8 cm, large arrows) represents a ‘‘superﬁcial ﬂuid alveologram’’ with comet-tail artifact (C); P, pleura.

Fig. 5. This lung exhibits a consolidated cranial lobe (arrows) with ramiﬁed hyperechoic air bronchograms and anechoic vessel cross-sections (V), and a liver-parenchyma-like echogenicity (5 MHz).

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and partially echogenic wall were bronchi (fluid bron-chograms) and the partially echogenic content, that moved synchronously with respiration, mucopurulent exudate (Fig. 6). Abscesses, which were found in deep lung tissue upon necropsy, could not be demonstrated by means of ultrasound, where the lung tissue covering the lesions contained air. In a calf in which consolida-tion of the cranial lobes was detected ultrasonographi-cally, muscular degeneration and diffuse atelectatic lung fields were revealed at necropsy, and a cow with hy-poechoic zones distributed across the surface of the lungs upon sonography showed septic pulmonary thrombi and pulmonary embolism at post mortem examination.

Where aspiration pneumonia was suspected upon physical examination (history: foul-smelling breath, dyspnoea, outstretched posture of the head and neck) mild abnormalities were found on the surface of the lungs, particularly in the cranioventral lobes, in the form of individual round hypoechoic zones with comet-tail artifacts upon sonography (Fig. 3). It was only in one patient that consolidation of the cranial lobes was found. At post mortem examination the mild sono-graphic abnormalities turned out to be gangrenous pneumonia.

In cattle with clinical symptoms of pleuritis and pleural eﬀusion, reduced resonance was detected on percussion of the chest. In all cases the pleural eﬀusion was bilateral. Fluid located in the pleural cavity ap-peared hypoechoic on ultrasonographic examination in

most cases (small amounts Fig. 7; larger amounts Fig. 8). Echogenic bands were seen in the hypoechoic fluid (Fig. 9) but at necropsy turned out to be fibrin. Floating echogenic material was also noted in the pleural fluid on the outer side of the pericardium (Fig. 10). The fluid led to compression atelectasis in the cranial lobes, which were seen as hypoechoic, and where

Fig. 7. Sonogram of a lung of a calf with pneumonia of the cranial lobe (13 MHz): mild (2 mm) anechoic ﬂuid deposit (FL) between the vis-ceral and parietal pleura; beneath that, a wedge-shaped consolidated zone (C) in the lung tissue, which causes dimpling of the visceral pleural surface of the lung and in which vessel structures are visible; P, pleura.

Fig. 8. Sonogram of a lung of a cow with moderate pleural eﬀusion (5 MHz): the lung with its irregular appearing surface (arrows) is dis-placed up to 2.5 cm from the chest wall by the hypoechoic ﬂuid (FL); P, pleura.

Fig. 9. Sonogram of a lung of a calf with fibrinous pleuritis (5 MHz): the atelectatic cranial lobe (CL) with hyperechoic air inclusion is floating in hypoechoic fluid (FL) through which fibrin septa are stretched, which are distinctly seen to float in real time mode; D, diaphragm.

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air was trapped in larger bronchi, they were hyperechoic with comet-tail artifacts (Fig. 9). In one patient, aside from fluid, a unilateral hypoechoic layer with the ultr-asonographic appearance of liver (dorsal) and a web-like lacy network of fibrin (ventral) of several cen-timetres thickness was noted between the parietal and visceral pleural surfaces of the lung. At post mortem examination, this area corresponded to marked fibrin exudation extending up to 10 cm thick between the parietal and visceral pleura. This displaced the lung tissue so far from the thoracic wall that it was no longer visible ultrasonographically. The heart was also dislo-cated from the chest wall and compressed (Figs. 11 and 12). In two animals with pleuritis, pleural effusion, and pneumonia, the lung tissue could not be assessed by means of sonography due to the large amount of fluid present (poor penetration).

Where ﬁndings from the physical examination poin-ted to TRP involving the pleural cavity and the lungs, echogenic coating and abscesses of the spleen, reticulum, the ruminal atrium and the ventral sac of the rumen (Figs. 14 and 15) as well as slowed or absent contrac-tions of the reticulum were determined upon sonogra-phy. In these patients, pleuritis and pleural eﬀusion (Figs. 11 and 12), or consolidation of the cranial lobes and comet-tail artifacts were additionally diagnosed. Three patients demonstrated, in addition to symptoms of acute pulmonary disease, signs of TRP upon physical examination, which were excluded on ultrasonography. The ultrasound examination of these animals revealed pulmonary disease alone.

The foreign body tests were positive in 20 and muscle tone of the abdominal wall increased in 40 of the 55 patients, although only nine animals were diagnosed with TRP by means of sonography. TRP involving the thorax diagnosed by means of ultrasound was confirmed by necropsy results in all nine cases. The abnormalities consisted of fibrinous layers and abscesses on the spleen, reticulum, ruminal atrium and rumen, as well as pneu-monia and fibrinous pleuritis with fluid deposits in the thoracic cavity (Figs. 11, 12, 14 and 15).

Fig. 11. Sonogram of the dorsal left side of the thorax of a cow with TRP (5 MHz): the irregular hypoechoic structure (ﬁbrin layer) is more than 20 cm thick and displaces the lung from the chest wall.

Fig. 12. Sonogram of the ventral left side of the thorax of a cow with TRP (3.5 MHz): the heart is displaced up to 15 cm from the left chest wall by anechoic ﬂuid (FL) and net-like echogenic ﬁbrin; RV, right ventricle; IVS, interventricular septum; LV, left ventricle.

Fig. 10. Sonogram of the heart of a calf with fibrinous pleuritis (5 MHz): the heart is displaced from the right chest wall by anechoic fluid (FL), on the outside of the pericardium, fibrinous layers are floating in the fluid; RV, right ventricle; IVS, interventricular septum; LV, left ventricle.

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4. Discussion

In human medicine, conventional radiographs are still the first applied diagnostic imaging procedure for thoracic examination (Mathis, 1996). In veterinary medicine, radiography is also superior to ultrasonogra-phy in the identification of diffuse diseases of lung pa-renchyma such as pulmonary emphysema, oedema, interstitial pneumonia and diffuse neoplastic or granu-lomatous processes, as well as abnormalities located

deep within lung tissue (Braun, 1997; Reef et al., 1991). X-ray examinations were not conducted in the present study due to cost and radiation safety reasons.

Sonography of the lungs is most often applied in human medicine secondarily in order to differentiate radiographic findings (Banholzer, 1993) and provides additional information on the morphology of processes largely devoid of air, which are attached to the chest wall (Lorenz, 1992). A primary indication for sono-graphic examination is the diagnosis of diseases of the thoracic and the pleural cavity (Mathis, 1996). The in-tercostal transmission of ultrasound where the lungs are air-filled extends only to the visceral pleura and ends at air-filled alveoli due to total reflection (Banholzer, 1993). Subpleural densities in lung parenchyma due to in-flammatory infiltration, neoplasia or emboli facilitate the penetration of ultrasound waves and thus sono-graphic representation (Mathis, 1996). Upon examina-tion of air-filled lung tissue, ultrasound waves are reflected back and forth on the border between tissue and lung parenchyma, simulating hyperechoic pulmon-ary structures in the form of reverberation artifacts. They form the characteristic echo pattern of the healthy thorax (Lorenz, 1992).

In horses and cattle, Reef (1998) and Scott (1998) reported that the replacement of alveolar air with ﬂuid causes the lung tissue to appear hypoechoic. The irreg-ularity of the visceral pleural surface of the lung due to unbalanced air content of the lung periphery can be a ﬁrst sign of consolidation. Comet-tail artifacts radiate from these nonaerated areas, created by small accumu-Fig. 14. Sonogram of the left cranioventral abdomen of a cow with

TRP (5 MHz): echogenic (ﬁbrinous) coating of the reticulum and ru-minal atrium.

Fig. 15. Sonogram of the left cranioventral abdomen of a cow with TRP (5 MHz): abscess (A) between reticulum, ruminal atrium and spleen (S) of 58 cm, distinct capsule and hypoechoic content. Fig. 13. Sonogram of the reticulum (R), ruminal atrium (AR) and

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lations of exudate, blood, mucus, oedema fluid, or tu-mour cells or by scarring subsequent to a previous bout of pneumonia or pleuritis. These small superficial hy-poechoic areas are homogeneous, consistent with ‘‘su-perficial fluid alveolograms’’ (Reef, 1998; Scott, 1998). Comet-tail artefacts are bright, ray-like stripes distal to a small structure whose impedance difference to the surrounding tissue is very large. They correspond to intensive multiple reflections (Braun, 1997).

In calves, Rabeling et al. (1998) have reported con-solidations as echogenic regions with comet-tail arti-facts. In the present study, consolidations were always hypoechoic. In pigs, Klein (1999) described hyperechoic zones (bronchograms) within hypoechoic fields (lung tissue devoid of air) at depths of more than 1 cm as a basic echogenic pattern. In accordance with the present study, this pattern was designated as a ‘‘severe lesion’’ when it covered an extensive area of lung tissue. Comet-tail artifacts and consolidated areas of mild severity (up to a maximum of 1 cm depth) represented mild to moderate abnormalities (Klein, 1999). Reef (1998) commented that the sonographic diagnosis of pulmon-ary parenchymal consolidation was based upon the de-tection of hypoechoic pulmonary parenchyma and bronchograms or vessels seen within it. Consolidation was observed most often cranioventrally, whereby the right lung was usually more severely affected in the horse (Reef, 1998). Extensive consolidation appeared as wedge-shaped hypoechoic, and often heterogeneous zones. The anechoic areas represent fluid-filled or ne-crotic areas. Hepatisation of lung parenchyma occurs with severe consolidation, resulting in an ultrasono-graphic appearance similar to that of a liver (Rabeling et al., 1998; Reef, 1998). In horses within a necrotic or consolidated lung, gas echoes may be attributable to gas formation by anaerobic bacteria, air from communi-cating bronchi, or focal areas of aerated lung (Reimer et al., 1989).

Pulmonary embolism in humans has been described by Schmidt (1997) as having hypoechoic, irregularly delimited, often wedge-shaped structures of varying echogenicity, often occurring in multiple configuration with accentuated vascularisation and sometimes mild accompanying effusion. Thus, the sonographic appear-ance of an embolism is not substantially different from that of pneumonia-associated consolidation as described by Reef (1998) in horses. In the present study, the hy-poechoic zones distributed across the surface of the lung in one cow with a pulmonary embolism was thought to be abnormal sonographic findings associated with pneumonia.

Pleural effusion appears as an anechoic space between the lung, thoracic wall, diaphragm and heart with acoustic enhancement deep to the lesion and often with septa floating within it. In horses suffering from pleural effusion, the pericardial-diaphragmatic ligament is often

seen in the ventral thorax upon sonography as a mem-brane running from the heart to the diaphragm (Reef, 1998). The results of our study showed that membra-nous structures were found at the same location, but in such a large number that the pericardial-diaphragmatic ligament could not be clearly distinguished from fibr-inous septa. In humans, the volume of fluid of free effusions can be reliably quantified by means of ultra-sound measurement and special calculation formulas (Lorenz, 1992). In horses, a pleural fluid line level with the point of the shoulder corresponds to the recovery of 1–5 L of pleural fluid per side (Reef, 1998). No mea-surement of intrapleural fluid was carried out in our study due to the presence of fibrinous pleuritis and compartmentation of the fluid-filled thorax that made extraction of the entire intrapleural fluid impossible.

Anechoic fluid represents transudate; increased ech-ogenicity points toward an increased cell count or total protein concentration (Braun et al., 1997; Reef et al., 1991). This feature is however, unreliable and must al-ways be confirmed by thoracocentesis (Lorenz, 1992). Free gas within the fluid is characterised by small, very bright in particular echoes in the dorsal fields (Braun et al., 1997; Reef et al., 1991; Reimer et al., 1989). Ac-cording to Braun et al. (1997) and Radostits et al. (2000), inflammatory pleural effusion is often present on only one side in cattle as the pleural cavities do not communicate with one another. In the patients we studied, inflammatory effusion was always present on both sides, albeit in varying degrees. Compression ate-lectasis occurs whenever the lung parenchyma is col-lapsed by fluid. The compressed lung is hypoechoic, of varying delimitation, exhibits changing size synchronous with respiration and can be partially re-ventilated fol-lowing thoracocentesis, as opposed to atelectasis due to obstruction (Reef, 1998; Schmidt, 1997).

Dry pleuritis is more diﬃcult to detect ultrasono-graphically because no ﬂuid separates parietal and vis-ceral pleural surfaces. Diagnosis requires the evaluation of the movement of the visceral pleural lung surface relative to the parietal pleural surface of the thoracic wall and diaphragm (‘‘gliding sign’’). If movement of the lung across the parietal pleural surfaces is rough or er-ratic, dry pleuritis is probably present. Absence of any movement between these surfaces during respiration is also an indication of dry pleuritis or adhesions between parietal and visceral pleural surfaces (Reef, 1998).

In cases of alveolar pulmonary emphysema, comet-tail artifacts extend from the lung surface (Braun, 1997). The sonographic ﬁnding of comet-tail artifacts in the present study was also characteristic of pulmonary em-physema. The reverberation artifacts found in healthy lung tissue were, for the most part, no longer visible. A further indication of this disease can be found in the inability to display the valve level of the heart, as was the case in three animals we examined. Daum (1992) and

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Lorenz (1992) have described the diﬃculties in the so-nographic examination of human patients with emphy-sema, because the ultrasound beam is completely dispersed by air.

TRP is characterised by an echogenic coating of the reticulum, spleen, ruminal atrium and rumen, as well as decreased or absent contractions of the reticulum (Braun, 1997; Fl€ock and Baumgartner, 2001). We found parts of the omentum and abomasum situated between the reticulum, ruminal atrium and abdominal wall sometimes led to diagnostic uncertainty. Additionally, the slowed or lack of reticular contractions was a dis-tinct indication of adhesions associated with foreign bodies. Foreign bodies could not be identiﬁed during the ultrasound examination because the top ridge wall cannot be penetrated by ultrasound waves. Also, during necropsy, foreign bodies were only rarely found because they had often already dispersed.

The lung surface is most often involved in cases of pulmonary disease (Scott, 1998). Therefore, not only can lung diseases be recognised, but the amount of lung tissue affected and the severity of illness can also be determined by means of sonography. This is essential for further treatment and the assessment of complica-tions. For example, a preliminary diagnosis of TRP with involvement of the pleural cavity or of fibrinous pleuritis due to pneumonia based on physical examination can be confirmed, excluding laparotomy or further treatment on account of the incurable prognosis, thus saving the animal owner further expense. In cases of pulmonary disease, where no actual TRP is present, foreign body tests can still be positive and sonography can aid in the decision as to whether laparotomy should or should not be performed.

The most profound lung changes can be found in most cases in the cranial and above all the cranioventral lung areas. Consequently, it is advisable to begin the sonographic examination in that location (Scott, 1998). In the present study, we found that the clinical, so-nographic and necropsy results in general corresponded well. Small consolidations (fluid alveologram) found during the ultrasound examination could not be fully confirmed with percussion. With large area consolida-tions, reduced resonance in the ventral lung area cor-responded well with the sonographic and necropsy results. The clinical and the sonographic diagnosis of emphysema were also demonstrated during necropsy. The extension and the severity of the lung changes could not be verified with clinical certainty in most cases, whereas this was possible most of the time with sonog-raphy, thus making the prognosis easier. They could not be verified only if intact lung tissue was located between the chest wall and pathologically changed lung tissue. Moreover, the case of severe emphysema in the context of bronchopneumonia, consolidations could partly not be identified due to numerous comet-tail artefacts.

Acknowledgements

I would like to thank the personnel of the Institute of Pathology and Forensic Veterinary Medicine of the University of Veterinary Medicine, Vienna for carrying out the necropsies.

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