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Clinical Commentary Complications incurred during treatment of horses for empyema of the guttural pouch J. D. PERKINS* AND J. SCHUMACHER† Department of Veterinary Clinical Sciences, Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Herts, UK; and †Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, 2407 River Drive, Knoxville, Tennessee 77901-1071, USA.

The article by Fogle et al. (2007) describes the uncommon complication of rupture of the guttural pouch encountered during lavage of the pouch to evacuate chondroids and demonstrates that even nonsurgical treatment for guttural pouch empyema is not completely safe. Guttural pouch empyema is the eventual outcome of bacterial infection of the guttural pouch, usually with Streptococcus equi ssp. equi or ssp. zooepidemicus (Newton et al. 1997; Judy et al. 1999). The water content of exudate within the guttural pouch diminishes as chronicity of the condition increases, transforming the exudate first to material having the consistency of cottage cheese and, aided by movements of the head that compress the exudate, to hard, spherical or ovoid concretions called chondroids (Judy et al. 1999). Fig 2: Endoscopic view of the medial compartment of the left Exudate within the guttural pouch can be removed guttural pouch of a horse with a chronic abscess in the conveniently, when entirely fluid, by lavage using a retropharyngeal lymph node after diode laser fenestration of the lymph node. inserted through the nasopharyngeal orifice of the pouch.

Fluid instilled into the pouch dilutes the thick, tenacious exudate, and with the exudate it exits through and around the catheter into the nasopharynx. The affected pouch can be lavaged through an indwelling catheter or through a catheter inserted on each occasion the pouch is lavaged. In addition to lavage, the horse should also receive topical and/or systemic antimicrobial therapy to aid resolution of infection (Verheyen et al. 2000). Because most infections of the guttural pouch are streptococcal, the antimicrobial drug of choice is a β-lactam antibiotic, such as penicillin, to which most streptococci are susceptible. The prognosis for recovery from infection and empyema of this nature with this treatment is excellent (Judy et al. 1999). Occasionally, empyema may recur despite repeated lavage, with or without systemic antibiotic Fig 1: Endoscopic view of the medial compartment of the left administration, possibly because of continued shedding of guttural pouch of a horse with a chronic abscess in the into the guttural pouch from a draining retropharyngeal lymph nodes that did not respond to repeated retropharyngeal lymph node abscess. The horse can be treated topical antibiotics and lavage. by creating, or enlarging, an opening between the lymph node and the guttural pouch with a laser (Figs 1 and 2). *Author to whom correspondence should be addressed. This treatment is not without risk, and the glossopharyngeal, EQUINE VETERINARY EDUCATION / AE / August 2007 357

Fig 3: Endoscopically guided snare removal of a guttural pouch Fig 5: Endoscopic view of the right guttural pouch of a pony chondroid. with an idiopathic pneumomediastinum and expiratory dyspnoea. Air has been forced from the mediastinun, between the fascial planes of the neck, and inverted the lining of the vagus and hypoglossal lying immediately ventral medial compartment of the guttural pouch. The reverse can to the floor of the medial compartment of the guttural pouch occur after rupture of the pharyngeal recess or medial can be damaged. compartment of the guttural pouch. When fluid within the guttural pouch becomes inspissated, its removal becomes more complicated, but small quantities of inspissated exudate with the consistency of A solution of N-acetylcysteine, a mucolytic agent, instilled cottage cheese can usually also be removed from the guttural into the guttural pouch has been reported to aid in the pouch by lavage. Removing large quantities becomes breakdown of inspissated exudate, thereby enhancing the problematic, however, because the lavage fluid is unable to efficacy of lavage (Bentz et al. 1996), but this treatment disperse freely through the exudate and dilute it and the remains unproven. One author (J.S.) placed chondroids nasopharyngeal orifice of the pouch, already partially removed from a guttural pouch in a jar containing occluded with the catheter, is too small to allow passage of N-acetylcysteine solution and a year later found no detectable solid exudate. Chondroids less then 2 cm in diameter can be dissolution of the chondroids. Perhaps constant agitation of removed with an endoscopically guided snare (Fig 3). To inspissated exudate in a medium of N-acetylcysteine, as remove large chondoids with a snare, the chondroids are cut would occur within a guttural pouch, is necessary to into small pieces with the snare, and the small pieces are then breakdown inspissated exudate. There is anecdotal evidence removed by either grasping with the snare or by lavage of the that N-acetylcysteine, used long-term, irritates the lining of pouch (Seahorn and Schumacher 1991). Chondroids too large the guttural pouch and may result in from to exit through the nasopharyngeal ostia have also been neuropraxia. We agree with Fogle et al. (2007) that when the removed through an artificial nasopharyngeal opening created majority of the guttural pouch is filled with chondroids, the with a laser (Hawkins et al. 2001). use of lavage, with or without the use of N-acetylcysteine is likely to be ineffectual. Inspissated exudate is removed surgically when nonsurgical removal has failed or is anticipated to fail, or when an endoscopic snare required for nonsurgical removal is not available. Surgery of the guttural pouch is frequently associated with complications. Incising into a guttural pouch is dangerous with any surgical approach because of the risk of damaging one or more of cranial nerves 9–12, or their branches (Mansmann and Wheat 1972; Haynes 1984; Freeman 1991). Damage to one or more cranial nerves, most commonly the glossopharyngeal nerve or the or its pharyngeal branch, during surgical exposure of the lumen of the guttural pouch is likely to result in temporary or permanent dysphagia (Mansmann and Wheat 1972; Haynes 1984). Inspissated exudate frequently causes no externally- apparent distension of the guttural pouch, making entry into Fig 4: Endoscopic view of the right guttural pouch of a horse the pouch more difficult than if the pouch had external with chondroids filling the guttural pouch up to the level of the ostia. These chondroids were all removed by endoscopic snare swelling because of difficulty in locating and penetrating the but the procedure took 8 h over 4 days. nondistended pouch. A Chamber’s catheter, inserted 358 EQUINE VETERINARY EDUCATION / AE / August 2007

normograde through the nasopharyngeal ostium, facilitates evacuating inspissated exudate from the pouch, frustration identification of and entry into a minimally-distended guttural associated with poor results may tempt the clinician to pouch and may reduce the likelihood of damaging a vessel or increase the amount of pressure used, and this may cranial nerve (Perkins et al. 2006). overwhelm the elasticity of the pouch causing it to rupture. Predicting when nonsurgical removal is likely to fail is Fogle et al. (2007) describe free gas and fluid in the sometimes difficult (Fogle et al. 2007). One horse in this report perilaryngeal area of horses after the guttural pouch has was treated by repeated lavage and snare removal of ruptured. Subcutaneous escape of air from the guttural pouch chondroids for 16 days before undergoing surgical treatment, causes subcutaneous emphysema that may, if left untreated, and the other horse, bilaterally affected with chondroids, was progress in severity and continue caudally down the neck. As treated similarly for 30 days before undergoing surgery to the horse swallows, the nasopharyngeal ostia open allowing evacuate the right guttural pouch. The left guttural pouch of influx of air into the pouches. Gravity and air pressure force this horse, thought to be 70–80% filled with chondroids, was gas and fluid to divide the fascial planes between the muscles cleared of chondroids after 23 days of lavage and snare of the neck, and as these fascial planes continue to divide, air removal, demonstrating that even pouches extensively filled and fluid enter the mediastinum initiating septic with inspissated exudate can sometimes be evacuated using pneumomediastinum, from which the horse is unlikely to nonsurgical means, and that predicting success or failure of recover, even with proper therapy (Fig 5). To prevent septic nonsurgical treatment is difficult. pneumomediastinum, exudate that has escaped from the Although surgical treatment may be expensive, a lengthy guttural pouch into surrounding tissue should be evacuated as period of nonsurgical treatment before surgical treatment is soon as possible, and fascial planes invaded by the exudate reported to dramatically increase the entire cost of treatment. should be exposed to establish proper drainage. We agree with the conclusions of Fogle et al. (2007) that surgical removal of these chondroids soon after the horses were presented may have been more expedient and more References economical, but these conclusions are made with the benefit Bentz, B.G., Dowd, A.L. and Freeman, D.E. (1996) Treatment of of hindsight. Criteria to determine when nonsurgical guttural pouch empyema with acetylcysteine irrigation. Equine treatment has a high probability of success in a reasonable Pract. 18, 33-35. amount of time would be helpful, but establishing such Fogle, C.A., Gerard, M.P. and Johansson, A. (2007) Spontaneous criteria is probably unfeasible. Recommendations, therefore, rupture of the guttural pouch as a complication of treatment for are biased by the clinician’s experience of a small population guttural pouch empyema. Equine vet. Educ. 19, 351-355. of affected horses and the surgeon’s expertise in surgical Freeman, D.E. (1991) Guttural pouches. In: Equine Respiratory removal of inspissated exudate/chondroids from a guttural Disorders, Ed: J. Beech, Lea & Febiger, Philadelphia. pp 305-330. pouch. We are not aware of any large studies on the incidence Haynes, P.F. (1984) Surgery of the equine respiratory tract. In: The of neuropraxia associated with guttural pouch surgery, but we Practice of Equine Surgery, Ed: P.B. Jennings, W.B. Saunders, both have had horses develop temporary neuropraxia after Philadelphia. pp 388-487. guttural pouch surgery. Hawkins, J.F., Frank, N., Sojka, J.E. and Levy, M.L. (2001) Fistulation of Based on our experience, we believe that nonsurgical the auditory tube diverticulum (guttural pouch) with a removal can be anticipated to fail when inspissated exudate neodymium:yttrium-aluminum-garnet laser for treatment of chronic empyema in two horses. J. Am. vet. med. Ass. is present in such a large quantity that it fills the pouch to the 218, 405-407. level of the nasopharyngeal opening of the pouch, Judy, C.E., Chaffin, M.K. and Cohen, N.D. (1999) Empyema of the determined radiographically or endoscopically (Fig 4), or guttural pouch (auditory tube diverticulum) in horses: 91 cases when large chondroids are so plentiful that mincing them (1977-1997). J. Am. vet. med. Ass. 215, 1666-1670. with an endoscopically guided snare is impractical. Because Mansmann, B.R. and Wheat, J.D. (1972) The diagnosis and treatment this procedure is time-consuming and difficult, many of equine upper respiratory disease. Proc. Am. Ass. equine clinicians may opt for surgical treatment after mincing only a Practnrs. 18, 337-379. few chondroids. We also believe that treatment by lavage Newton, J.R., Wood, J.L.N., Dunn, M.N., De Brauwere, N.M. and should be abandoned if the quantity of exudate within the Chanter, N. (1997) Naturally occurring persistent and affected pouch is not dramatically reduced after several days asymptomatic infection of the guttural pouches of horses with of treatment. Streptococcus equi. Vet. Rec. 140, 84-90. One author (J.P.) has treated 2 horses that incurred rupture Perkins, J.D., Schumacher, J., Kelly, G., Gomez, J.H. and Schumacher, of a guttural pouch during high pressure lavage. The guttural J. (2006) Surgical removal of inspissated exudate from the guttural pouch of 10 standing horses. Vet. Surg. 35, 658-662. pouch of one of these horses was lavaged with a manually operated fluid pump attached to a foal stomach tube inserted Seahorn, T.L. and Schumacher, J. (1991) Nonsurgical removal of chondroid masses from the guttural pouch of two horses. J. Am. into the guttural pouch and occupied most of the pouch’s vet. med. Ass. 199, 368-369. nasopharyngeal orifice. Rupture was likely to have occurred Verheyen, K., Newton, J.R., Talbot, N.C., De Brauwere, N.M. and because the tube prevented the fluid pumped into the pouch Chanter, N. (2000) Elimination of guttural pouch infection and from exiting through the nasopharyngeal ostia. Although high inflammation in asymptomatic carriers of Streptococcus equi. pressure lavage may be more effective than gravity flow in Equine vet. J. 32, 527-532.