EQUINE VETERINARY JOURNAL
22
Equine vet. J . (1991) 23 (1) 22-24
Cranial thoracic masses in the horse: a sequel to pleuropneumonia T. D. BYARS, C. M. DAINIS, K. L. SELTZER and N. W. RANTANEN* Hagyard-Davidson-McGeeAssociates F?S.C., 848 V Nandino Boulevard, Lexington, Kentucky 40511, *PO Box 11849, Lexington, Kentucky 40578- 1849, USA. Summary
Introduction
The formation of cranial thoracic masses (CTM) as a sequel to infectious pleuropneumonia is described. Using ultrasound, masses were diagnosed subjectively as abscesses or loculations. Eight of 99 cases with pleuropneumonia had CTM. Clinical signs associated with the presence of a CTM included increased heart rate, jugular distention, forelimb 'pointing' and caudal displacement of the heart. Techniques used for diagnostic ultrasonographic examination of the cranial thorax are described. Five of the eight horses with CTM responded to conservative medical management; the other three required percutaneous drainage of the mass to relieve worsening signs of cardiac decompensation. Improvements in cardiovascular parameters were evident within 12 h of drainage. The indications for and limitations of invasive drainage of cranial thoracic masses are discussed.
INFECTIOUS pleuropneumonia in the horse can be the result of pulmonary abscessation (Mair and Lane 1989) or lead to abscessation secondary to pulmonary infection and necrosis. Chronic pleuropneumonia can compromise cardiac function either from concurrent constrictive or effusive pericarditis (Dill 1987), cor pulmonale, or the formation of space occupying abscesses or loculated masses which impinge upon, or displace, the heart. The organisms involved in the infectious process may be aerobic or anaerobic and may respond to systemic treatment (Sweeney, Divers and Benson 1985; Semrad and Byars 1988). In man, abscesses not responsive to systemic therapy may require surgical drainage (Penn and George 1985). The precise location of thoracic abscesses which cause clinical signs of cardiovascular compromise in the horse have not been described. A decision regarding medical and/or surgical
TABLE 1: Clinical data on eight horses with pleuropneumonia and cranial thoracic masses (CTM)
Case Age
Hospitalisation days until Tracheal Sex Breed massformation wash
5months C
Tb
8
Strep zooepidemicus
3years
C
Tb
8
3 years
F
Std
'2
Strep zooepidemicus E. coli E. coli
5years
S
Tb
14
5years
F
Tb
28
6years
F
Tb
11
6years
S
Tb
14
6years
S
Tb
4
Enterobacter aglomerans E. coli.
Pleural fluid Strep zooepidemicus Pseudomonassp. Strep zooepidemicus E. coli Strep zooepidemicus No growth
No. of cranial CTM Cranial abscess thoracic ultrasound or loculation drainage evaluation Strep zooepidemicus
5
Loculation/ Survived abscessation
'*N/D
0
Abscessation Survived
N/D
0
Abscessation Survived
N/D
0
Loculation
Enterobacter sp. Bacteroides 5 E. coli. fragilis beta Streptococcus Peptostreptococcus sp. No growth 1 Strep Strep zooepidemicus zooepidemicus E. coli E. coli E. coli Yersinia Rhodococcus N/D 0 pseudotuberculosis equi Yersinia pseudotuberculosis Klebsiellaoxyioca 0 Klebsiella Klebsiella N/D pneumoniae pneumoniae Enterococcus sp. Enterococcus sp.
*: Sick 3 weeks prior to hospital admission: "N/D:
not determined
Outcome
Survived
Loculation/ Destroyed abscessation Loculation/ Survived abscessation Loculation
Survived
Loculation
Survived
EQUINE VETERINARY JOURNAL
23
management of infected thoracic lesions is aided by localisation of a mass and an assessment of the degree of compromise to vital organs within the thoracic cavity. The purpose of this retrospective study was to describe cranial thoracic masses (CTM) in the horse as a sequel to pleuropneumonia and the clinical signs associated with compression or displacement of the heart.
Case histories From January 1984 to the end of December 1986, 99 cases of pleuropneumonia were referred to the Hagyard-Davidson-McGee Equine Medical Facility in Lexington, Kentucky. Eight horses, aged five months to six years, were identified as having CTM and are described in Table 1. The horses were presented after examination by the referring veterinarians with varying degrees of anorexia, fever, nasal discharge, respiratory distress or weight loss.
Clinical findings The clinical findings in the eight horses were compatible with infectious pleuropneumonia and confirmed by ultrasonography. Vital signs included temperatures of 100.4 to 104.6"F, heart rates of 36 to 92 beats per min and respiratory rates of 20 to 48 breaths per min. Clinical signs of a CTM in the eight horses studied were found two to 28 days post hospitalisation and included elevation of heart rate in five horses (63 per cent), jugular distention in eight horses (100 per cent), 'pointing' of a forelimb in six (75 per cent) and subjective auscultation of caudal heart displacement in eight (100 per cent). Three horses also had jugular thrombosis. Ventral oedema was an inconsistent finding. The clinical findings are present in Table 2. Ultrasonography (Advanced Technology Laboratories, Washington, USA) was used to confirm caudal cardiac displacement and the presence of an encapsulated abscess, empyema or loculations cranial to the heart. To locate the lesion, the ultrasound cardiac scan head (3.0 mHz) was placed between the 2nd to 4th intercostal space while one forelimb was held off the ground in a forward position. Masses appeared as either multiple fluid-filled loculated lesions or thick walled pockets with cellular and inspissated debris consistent with an abscess (Rantanen 1986). Figure 1 is an ultrasonographic photograph from Case 1 showing an abscess. The degree of cardiovascular compromise was assessed by elevation of heart rate, jugular distention, variable increase in subcutaneous oedema and echocardiographic examination. Bacterial isolates were obtained from tracheal washes, pleural fluid aspirates or CTM drainage. Tracheal and pleural fluid aspirates yielded similar results in four of the eight horses sampled. Table I details the bacterial isolates obtained. CTM fluid samples for bacterial isolation and cytology were obtained in three of the eight horses. Invasive sampling was not performed in the remaining five horses which were stable or showing
ultrasonographic evidence of decreasing size of the CTM. The three samples obtained contained cell types (primarily neutrophils) and volumes consistent with abscessation. A consistent gram positive aerobe, Streptococcus zooepidemicus, was obtained from Case 1 which was drained on five occasions. Anaerobic Bacteroides fragilis and Pepto-streptococcus sp were isolated from Case 2 and no bacterial growth was obtained from the drainage of Case 5. Seven of the eight horses with CTM survived.
Differential diagnoses The differential diagnoses of a CTM in horses with infectious pleuropneumonia include other causes of cardiovascular compromise (effusive or constrictive pericarditis) and lameness which could result in forelimb pointing. Sole abscesses, navicular disease or unilateral laminitis should be considered. Lymphosarcoma may be considered in cases of non-infectious pleural effusion associated with cardiac compromise and ultrasonographic findings of solid thoracic masses. A cranial thoracic location of neoplastic lesions has not been described in the living horse. However, ultrasonographic examination cranial to the heart is not a routine procedure. Cranial thoracic lymphosarcoma lesions have been described post mortem (Mair, Lane and Lucke 1985). I
Treatment Five of the eight horses responded to conservative medical management. Systemic antimicrobial therapy was based on the results of bacterial culture and sensitivity from thoracic fluids and transtracheal aspirates (Semrad and Byars 1988). Case 3 showed signs consistent with a CTM and this was confirmed on the second day after admission. This mare had not had any previous thoracic invasive procedures and presented with bilateral jugular thrombosis. The thrombosis was originally attributed to intravenous (iv) injections administered at the farm during the three weeks of treatment prior to hospitalisation. In retrospect, this finding may have been due to the presence of a CTM with secondary venous congestion. Invasive drainage of the CTM was performed for Cases 1,5, and 6. Each horse was anaesthetised with 0.5 mg/kg bodyweight (bwt) xylazine HCI (Rompun) iv followed by 2 m a g (bwt) ketamine HCI (Ketaset). The choice of left or right lateral recumbency was based on ultrasonographic findings of the most
TABLE 2: Clinical signs present after diagnosis' of a cranial thoracic mass (CTM) Case 1 2 3 4 5 6 7 8
Heart 'Caudal cardiac Jugular Forelimb rate displacement distention Thrombosis pointing 92 64 68 48 76 60 52 80
+
+ +
+
+ +
+ +
'ultrasonographic diagnosis
+ + + + +
+ + +
+ (bilateral) (bilateral) (unilateral)
+
+ + + + Fig I : 8.3 cm abscess in the cranial thorax (arrows) with compositefluid in a,five-month-old Thoroughhred foal (Case I )
EQUINE VETERINARY JOURNAL
24
available 'window' into the abscess as determined in the standing position. In recumbency, the forelimb was held cranial by an assistant, and the 'window' areas was examined again by ultrasound, The site was prepared by aseptic technique, a stab incision through the skin was made using a number 10 scalpel blade and a sharp open-tipped thoracic catheter (Argyle 24 french, 16 inch catheter) was introduced quickly into the abscess cavity. The trocar was removed and fluid samples obtained for culture and cytology. Mechanical suction was applied to the cannula and the abscess drained. The tube was withdrawn and a single skin suture placed to enclose the incision site. The horse was then allowed to recover from anaesthesia. The drainage procedure was obtained by 'trial and error'. An attempt to drain the abscess in Case 1 was originally performed in the standing position under heavy sedation using a 4 inch teat cannula at the site identified by ultrasonographic examination. Inadequate immobilisation on this occasion resulted in incomplete drainage and the cannula being moved by the adjacent heart. On another occasion in Case 1, a thoracic cannula was left in situ. After anaesthetic recovery, cardiac dysrhythmia and clinical evidence of distress was noted. The tube was removed immediately and the colt became asymptomatic. In Case 5, lavage of the abscess cavity was performed during anaesthesia on two occasions using one litre of normal saline with 10 million iu sodium penicillin (Squibb). No benefit was derived from this procedure and consistent recurrence necessitated euthanasia. Bacteroides fragilis was eventually isolated, and therefore a more appropriate antimicrobial may have prevented abscess reformation. In the cases which required CTM drainage, abatement of clinical signs was usually noted within 12 h. Heart rate returned to normal, jugular distention ceased and appetite improved. Discomfort at the drainage site was displayed by increased lameness and 'pointing' immediately after the procedure. Non-steroidal anti-inflammatory medications were used during the recuperative phase (6 to 12 h). In Cases 1 and 5, multiple drainage was required because clinical signs associated with the CTM returned at six to nine day intervals. Case 6 was drained once. In the five horses which did not require drainage, clinical signs were considered moderate. Supportive treatment consisted of intermittent furosemide (Lasix; 0.5 mgkg bwt iv or im), nonsteroidal anti-inflammatory drugs and dietary salt restriction. Case 5 was destroyed and necropsy findings were consistent with the ultrasonographic lesions determined antemortem. No primary cardiac disease was found.
caudal than normal, to avoid overlooking a cranially located abscess. Loculations were considered to be lesions not confirmed as abscesses although the clinical signs did not distinguish these horses from those determined to have an abscess (Table 1). In the horses studied, differentiating loculations from abscessation did not provide information which implied changes in prognosis or therapy. In Cases 1, 5 and 6, loculation was noted ultrasonographically prior to abscessation and indicates the abscesses were not the result of mediastinal lymph node abscessation. The finding of a CTM with clinical signs in Case 3 prior to any thoracic invasive procedure suggest the lesion is not iatrogenically induced. A CTM should be suspected in cases of infectious pleuropneumonia whenever clinical signs consistent with cardiovascular compromise or forelimb pointing are noted. The development of these lesions may be related to gravitational forces. Ultrasound examination of horses with pleuropneumonia often reveal the heart and pericardium displaced from the right moracic wall by fluid, usually containing fibrin. If this region becomes 'walled-off, the effusions can result in displacement of the heart. In this study, however, caudal cardiac displacement was only noted on the left side of the thorax. The concurrent clinical signs of cardiac decompensation may be associated with the more solid mass of an abscess impinging on the heart together with some degree of displacement. In horses in which the CTM was drained, clinical signs resolved either intermittently or permanently which suggests the CTM was responsible for the signs. CTMs have not been found in horses without infectious pleuropneumonia which further suggests that this lesion is a true sequel to the episode of pleuropneumonia. Most of the horses with a CTM did not require drainage. Conservative treatment was found to be effective in the majority of cases. It is doubtful, therefore, that early drainage is indicated to facilitate a rapid recovery. Drainage should be considered only for medically non-responsive patients with consideration of the inherent risks of anaesthesia and sharp penetration near vital structures. If drainage or sampling of a CTM is elected, the procedure is not recommended in the standing patient. In our experience, reliable positioning and immobilisation were more difficult without a short term general anaesthetic. A CTM should be considered as a sequel to infectious pleuropneumonia and has not previously been described. Recognition and appropriate treatment usually results in a resolution of the lesion and its associated clinical signs.
Acknowledgements Discussion Diagnosis of a CTM was made by ultrasonographic examination. Horses with significant effusion in the thoracic cavity occasionally have fluid in the space cranial to the heart as well. It is important to examine the cranial thoracic space repeatedly to confirm that fluid is decreasing throughout the course of treatment. Formation of an abscess wall, trapping exudate cranial to the heart, will not allow drainage by conventional methods. It is usually necessary to hold the limb forward to allow easy access to the cranial thoracic space for adequate examination. Cranial thoracic abscesses are characterised by a dense wall containing composite fluid displacing the cranial lung lobes dorsally. Exudate may be seen outside the abscess wall and fibrin strands may be attached to the outer wall. If the abscess is large enough, the heart will be displaced caudally and cranial cardiac structures can be seen on routine ultrasound examination. It is important to examine the cranial thorax in horses with pleuropneumonia, especially if cardiac structures are found more
The authors wish to thank Ms. Kimberly Ellis for her patience and assistance in the preparation of this manuscript.
References Dill. S. G . (1987) Fibrinous pericarditis. In: Current Tlterop? in Equine Medicine I / . W. B. Saunders. Philadelphia. pp171-172. Mair, T. S . and Lane, J. G. (1989) Pneumonia, lung abscesses and pleuritis in adult horses: a review of 5 I cases. Equine vcf.J. 21, 175-180. Mair, T. S.. Lane, J. G . and Lucke. V. M. (1985) Clinicopathological features of lymphosarcorna involving the thoracic cavity. Equine wf. J. 17,428-433. Penn. R. L. and George R. B. (1985) Lung abscess, In: Current Therapy in Inrerual Medicine 1984-1985. B. C. Decker, Philadclphia. pp766-769. Rantanen. N. W. (1986) Diseases of the thorax. Diagnostic ultrasound. Vet. Clin. N. Am. 2.49-66. Sernrad. S. and Byars, T. D. (1988) Overview of pleuritis and pleural effusion in the horse. Proc. 6th Am. C ~ l lVet. . In!. Med. Forum. 616-618. Sweeney. C. R., Divers, T.J. and Benson. C. E. (1985) Anaerobic bacteria in 21 horses with pleuropneumonia. J.Am. vet. med. Ass. 187.72 1-724.
Received for publication: 22.9.89 Accepted: 13.2.90
22
Equine vet. J . (1991) 23 (1) 22-24
Cranial thoracic masses in the horse: a sequel to pleuropneumonia T. D. BYARS, C. M. DAINIS, K. L. SELTZER and N. W. RANTANEN* Hagyard-Davidson-McGeeAssociates F?S.C., 848 V Nandino Boulevard, Lexington, Kentucky 40511, *PO Box 11849, Lexington, Kentucky 40578- 1849, USA. Summary
Introduction
The formation of cranial thoracic masses (CTM) as a sequel to infectious pleuropneumonia is described. Using ultrasound, masses were diagnosed subjectively as abscesses or loculations. Eight of 99 cases with pleuropneumonia had CTM. Clinical signs associated with the presence of a CTM included increased heart rate, jugular distention, forelimb 'pointing' and caudal displacement of the heart. Techniques used for diagnostic ultrasonographic examination of the cranial thorax are described. Five of the eight horses with CTM responded to conservative medical management; the other three required percutaneous drainage of the mass to relieve worsening signs of cardiac decompensation. Improvements in cardiovascular parameters were evident within 12 h of drainage. The indications for and limitations of invasive drainage of cranial thoracic masses are discussed.
INFECTIOUS pleuropneumonia in the horse can be the result of pulmonary abscessation (Mair and Lane 1989) or lead to abscessation secondary to pulmonary infection and necrosis. Chronic pleuropneumonia can compromise cardiac function either from concurrent constrictive or effusive pericarditis (Dill 1987), cor pulmonale, or the formation of space occupying abscesses or loculated masses which impinge upon, or displace, the heart. The organisms involved in the infectious process may be aerobic or anaerobic and may respond to systemic treatment (Sweeney, Divers and Benson 1985; Semrad and Byars 1988). In man, abscesses not responsive to systemic therapy may require surgical drainage (Penn and George 1985). The precise location of thoracic abscesses which cause clinical signs of cardiovascular compromise in the horse have not been described. A decision regarding medical and/or surgical
TABLE 1: Clinical data on eight horses with pleuropneumonia and cranial thoracic masses (CTM)
Case Age
Hospitalisation days until Tracheal Sex Breed massformation wash
5months C
Tb
8
Strep zooepidemicus
3years
C
Tb
8
3 years
F
Std
'2
Strep zooepidemicus E. coli E. coli
5years
S
Tb
14
5years
F
Tb
28
6years
F
Tb
11
6years
S
Tb
14
6years
S
Tb
4
Enterobacter aglomerans E. coli.
Pleural fluid Strep zooepidemicus Pseudomonassp. Strep zooepidemicus E. coli Strep zooepidemicus No growth
No. of cranial CTM Cranial abscess thoracic ultrasound or loculation drainage evaluation Strep zooepidemicus
5
Loculation/ Survived abscessation
'*N/D
0
Abscessation Survived
N/D
0
Abscessation Survived
N/D
0
Loculation
Enterobacter sp. Bacteroides 5 E. coli. fragilis beta Streptococcus Peptostreptococcus sp. No growth 1 Strep Strep zooepidemicus zooepidemicus E. coli E. coli E. coli Yersinia Rhodococcus N/D 0 pseudotuberculosis equi Yersinia pseudotuberculosis Klebsiellaoxyioca 0 Klebsiella Klebsiella N/D pneumoniae pneumoniae Enterococcus sp. Enterococcus sp.
*: Sick 3 weeks prior to hospital admission: "N/D:
not determined
Outcome
Survived
Loculation/ Destroyed abscessation Loculation/ Survived abscessation Loculation
Survived
Loculation
Survived
EQUINE VETERINARY JOURNAL
23
management of infected thoracic lesions is aided by localisation of a mass and an assessment of the degree of compromise to vital organs within the thoracic cavity. The purpose of this retrospective study was to describe cranial thoracic masses (CTM) in the horse as a sequel to pleuropneumonia and the clinical signs associated with compression or displacement of the heart.
Case histories From January 1984 to the end of December 1986, 99 cases of pleuropneumonia were referred to the Hagyard-Davidson-McGee Equine Medical Facility in Lexington, Kentucky. Eight horses, aged five months to six years, were identified as having CTM and are described in Table 1. The horses were presented after examination by the referring veterinarians with varying degrees of anorexia, fever, nasal discharge, respiratory distress or weight loss.
Clinical findings The clinical findings in the eight horses were compatible with infectious pleuropneumonia and confirmed by ultrasonography. Vital signs included temperatures of 100.4 to 104.6"F, heart rates of 36 to 92 beats per min and respiratory rates of 20 to 48 breaths per min. Clinical signs of a CTM in the eight horses studied were found two to 28 days post hospitalisation and included elevation of heart rate in five horses (63 per cent), jugular distention in eight horses (100 per cent), 'pointing' of a forelimb in six (75 per cent) and subjective auscultation of caudal heart displacement in eight (100 per cent). Three horses also had jugular thrombosis. Ventral oedema was an inconsistent finding. The clinical findings are present in Table 2. Ultrasonography (Advanced Technology Laboratories, Washington, USA) was used to confirm caudal cardiac displacement and the presence of an encapsulated abscess, empyema or loculations cranial to the heart. To locate the lesion, the ultrasound cardiac scan head (3.0 mHz) was placed between the 2nd to 4th intercostal space while one forelimb was held off the ground in a forward position. Masses appeared as either multiple fluid-filled loculated lesions or thick walled pockets with cellular and inspissated debris consistent with an abscess (Rantanen 1986). Figure 1 is an ultrasonographic photograph from Case 1 showing an abscess. The degree of cardiovascular compromise was assessed by elevation of heart rate, jugular distention, variable increase in subcutaneous oedema and echocardiographic examination. Bacterial isolates were obtained from tracheal washes, pleural fluid aspirates or CTM drainage. Tracheal and pleural fluid aspirates yielded similar results in four of the eight horses sampled. Table I details the bacterial isolates obtained. CTM fluid samples for bacterial isolation and cytology were obtained in three of the eight horses. Invasive sampling was not performed in the remaining five horses which were stable or showing
ultrasonographic evidence of decreasing size of the CTM. The three samples obtained contained cell types (primarily neutrophils) and volumes consistent with abscessation. A consistent gram positive aerobe, Streptococcus zooepidemicus, was obtained from Case 1 which was drained on five occasions. Anaerobic Bacteroides fragilis and Pepto-streptococcus sp were isolated from Case 2 and no bacterial growth was obtained from the drainage of Case 5. Seven of the eight horses with CTM survived.
Differential diagnoses The differential diagnoses of a CTM in horses with infectious pleuropneumonia include other causes of cardiovascular compromise (effusive or constrictive pericarditis) and lameness which could result in forelimb pointing. Sole abscesses, navicular disease or unilateral laminitis should be considered. Lymphosarcoma may be considered in cases of non-infectious pleural effusion associated with cardiac compromise and ultrasonographic findings of solid thoracic masses. A cranial thoracic location of neoplastic lesions has not been described in the living horse. However, ultrasonographic examination cranial to the heart is not a routine procedure. Cranial thoracic lymphosarcoma lesions have been described post mortem (Mair, Lane and Lucke 1985). I
Treatment Five of the eight horses responded to conservative medical management. Systemic antimicrobial therapy was based on the results of bacterial culture and sensitivity from thoracic fluids and transtracheal aspirates (Semrad and Byars 1988). Case 3 showed signs consistent with a CTM and this was confirmed on the second day after admission. This mare had not had any previous thoracic invasive procedures and presented with bilateral jugular thrombosis. The thrombosis was originally attributed to intravenous (iv) injections administered at the farm during the three weeks of treatment prior to hospitalisation. In retrospect, this finding may have been due to the presence of a CTM with secondary venous congestion. Invasive drainage of the CTM was performed for Cases 1,5, and 6. Each horse was anaesthetised with 0.5 mg/kg bodyweight (bwt) xylazine HCI (Rompun) iv followed by 2 m a g (bwt) ketamine HCI (Ketaset). The choice of left or right lateral recumbency was based on ultrasonographic findings of the most
TABLE 2: Clinical signs present after diagnosis' of a cranial thoracic mass (CTM) Case 1 2 3 4 5 6 7 8
Heart 'Caudal cardiac Jugular Forelimb rate displacement distention Thrombosis pointing 92 64 68 48 76 60 52 80
+
+ +
+
+ +
+ +
'ultrasonographic diagnosis
+ + + + +
+ + +
+ (bilateral) (bilateral) (unilateral)
+
+ + + + Fig I : 8.3 cm abscess in the cranial thorax (arrows) with compositefluid in a,five-month-old Thoroughhred foal (Case I )
EQUINE VETERINARY JOURNAL
24
available 'window' into the abscess as determined in the standing position. In recumbency, the forelimb was held cranial by an assistant, and the 'window' areas was examined again by ultrasound, The site was prepared by aseptic technique, a stab incision through the skin was made using a number 10 scalpel blade and a sharp open-tipped thoracic catheter (Argyle 24 french, 16 inch catheter) was introduced quickly into the abscess cavity. The trocar was removed and fluid samples obtained for culture and cytology. Mechanical suction was applied to the cannula and the abscess drained. The tube was withdrawn and a single skin suture placed to enclose the incision site. The horse was then allowed to recover from anaesthesia. The drainage procedure was obtained by 'trial and error'. An attempt to drain the abscess in Case 1 was originally performed in the standing position under heavy sedation using a 4 inch teat cannula at the site identified by ultrasonographic examination. Inadequate immobilisation on this occasion resulted in incomplete drainage and the cannula being moved by the adjacent heart. On another occasion in Case 1, a thoracic cannula was left in situ. After anaesthetic recovery, cardiac dysrhythmia and clinical evidence of distress was noted. The tube was removed immediately and the colt became asymptomatic. In Case 5, lavage of the abscess cavity was performed during anaesthesia on two occasions using one litre of normal saline with 10 million iu sodium penicillin (Squibb). No benefit was derived from this procedure and consistent recurrence necessitated euthanasia. Bacteroides fragilis was eventually isolated, and therefore a more appropriate antimicrobial may have prevented abscess reformation. In the cases which required CTM drainage, abatement of clinical signs was usually noted within 12 h. Heart rate returned to normal, jugular distention ceased and appetite improved. Discomfort at the drainage site was displayed by increased lameness and 'pointing' immediately after the procedure. Non-steroidal anti-inflammatory medications were used during the recuperative phase (6 to 12 h). In Cases 1 and 5, multiple drainage was required because clinical signs associated with the CTM returned at six to nine day intervals. Case 6 was drained once. In the five horses which did not require drainage, clinical signs were considered moderate. Supportive treatment consisted of intermittent furosemide (Lasix; 0.5 mgkg bwt iv or im), nonsteroidal anti-inflammatory drugs and dietary salt restriction. Case 5 was destroyed and necropsy findings were consistent with the ultrasonographic lesions determined antemortem. No primary cardiac disease was found.
caudal than normal, to avoid overlooking a cranially located abscess. Loculations were considered to be lesions not confirmed as abscesses although the clinical signs did not distinguish these horses from those determined to have an abscess (Table 1). In the horses studied, differentiating loculations from abscessation did not provide information which implied changes in prognosis or therapy. In Cases 1, 5 and 6, loculation was noted ultrasonographically prior to abscessation and indicates the abscesses were not the result of mediastinal lymph node abscessation. The finding of a CTM with clinical signs in Case 3 prior to any thoracic invasive procedure suggest the lesion is not iatrogenically induced. A CTM should be suspected in cases of infectious pleuropneumonia whenever clinical signs consistent with cardiovascular compromise or forelimb pointing are noted. The development of these lesions may be related to gravitational forces. Ultrasound examination of horses with pleuropneumonia often reveal the heart and pericardium displaced from the right moracic wall by fluid, usually containing fibrin. If this region becomes 'walled-off, the effusions can result in displacement of the heart. In this study, however, caudal cardiac displacement was only noted on the left side of the thorax. The concurrent clinical signs of cardiac decompensation may be associated with the more solid mass of an abscess impinging on the heart together with some degree of displacement. In horses in which the CTM was drained, clinical signs resolved either intermittently or permanently which suggests the CTM was responsible for the signs. CTMs have not been found in horses without infectious pleuropneumonia which further suggests that this lesion is a true sequel to the episode of pleuropneumonia. Most of the horses with a CTM did not require drainage. Conservative treatment was found to be effective in the majority of cases. It is doubtful, therefore, that early drainage is indicated to facilitate a rapid recovery. Drainage should be considered only for medically non-responsive patients with consideration of the inherent risks of anaesthesia and sharp penetration near vital structures. If drainage or sampling of a CTM is elected, the procedure is not recommended in the standing patient. In our experience, reliable positioning and immobilisation were more difficult without a short term general anaesthetic. A CTM should be considered as a sequel to infectious pleuropneumonia and has not previously been described. Recognition and appropriate treatment usually results in a resolution of the lesion and its associated clinical signs.
Acknowledgements Discussion Diagnosis of a CTM was made by ultrasonographic examination. Horses with significant effusion in the thoracic cavity occasionally have fluid in the space cranial to the heart as well. It is important to examine the cranial thoracic space repeatedly to confirm that fluid is decreasing throughout the course of treatment. Formation of an abscess wall, trapping exudate cranial to the heart, will not allow drainage by conventional methods. It is usually necessary to hold the limb forward to allow easy access to the cranial thoracic space for adequate examination. Cranial thoracic abscesses are characterised by a dense wall containing composite fluid displacing the cranial lung lobes dorsally. Exudate may be seen outside the abscess wall and fibrin strands may be attached to the outer wall. If the abscess is large enough, the heart will be displaced caudally and cranial cardiac structures can be seen on routine ultrasound examination. It is important to examine the cranial thorax in horses with pleuropneumonia, especially if cardiac structures are found more
The authors wish to thank Ms. Kimberly Ellis for her patience and assistance in the preparation of this manuscript.
References Dill. S. G . (1987) Fibrinous pericarditis. In: Current Tlterop? in Equine Medicine I / . W. B. Saunders. Philadelphia. pp171-172. Mair, T. S . and Lane, J. G. (1989) Pneumonia, lung abscesses and pleuritis in adult horses: a review of 5 I cases. Equine vcf.J. 21, 175-180. Mair, T. S.. Lane, J. G . and Lucke. V. M. (1985) Clinicopathological features of lymphosarcorna involving the thoracic cavity. Equine wf. J. 17,428-433. Penn. R. L. and George R. B. (1985) Lung abscess, In: Current Therapy in Inrerual Medicine 1984-1985. B. C. Decker, Philadclphia. pp766-769. Rantanen. N. W. (1986) Diseases of the thorax. Diagnostic ultrasound. Vet. Clin. N. Am. 2.49-66. Sernrad. S. and Byars, T. D. (1988) Overview of pleuritis and pleural effusion in the horse. Proc. 6th Am. C ~ l lVet. . In!. Med. Forum. 616-618. Sweeney. C. R., Divers, T.J. and Benson. C. E. (1985) Anaerobic bacteria in 21 horses with pleuropneumonia. J.Am. vet. med. Ass. 187.72 1-724.
Received for publication: 22.9.89 Accepted: 13.2.90
