526
knowledge of vascular anatomy. These techniques are further
complicated by the fact that a percentage of horses exhibit
variations in the vascular anatomy of the affected vessels,
particularly the carotid trifurcation (Freeman et al. 1993). For
this reason, the use of most of the surgical procedures described
is confined to specialist practices.
Complications associated with surgical treatment include
failure to prevent epistaxis and the development of
neurological disorders and blindness following surgery. The
mechanism for the development of these complications is not
well understood and the incidence varies with the technique
used, such that ligation techniques carry the highest risk
(Freeman et al. 1990). Nevertheless owners should be warned
of these potential complications prior to surgery.
Outcome and prognosis
Successful treatment of guttural pouch mycosis is dependant
upon early recognition and prompt intervention by attending
clinicians. Identification of cases presenting with clinical signs
of epistaxis or fungal plaques overlying major vessels should
be considered an emergency and the owners, trainers or
keepers informed of the potentially fatal outcome. Affected
animals should be moved to a suitable establishment where
treatment is available.
Transarterial coil embolisation techniques are the currently
accepted gold standard for treatment, and using this technique
Lepage and Piccot-Cr?zollet (2005) reported a survival rate of
87%, with 71% of horses returning to a satisfactory level of
exercise. Mycotic lesions generally show complete regression
within 4 months of treatment with this technique.
A poor prognosis should be given if there are clinical signs
of neurological disease, particularly dysphagia, prior to
treatment. In some horses with neurological deficits, including
evidence of left recurrent laryngeal nerve dysfunction and
Horner?s syndrome, prior to treatment, complete resolution
does occur but can take up to 18 months.
Summary
In summary guttural pouch mycosis is an uncommon but
potentially fatal disease affecting horses of all ages, breeds
and sex. The most common presenting signs include epistaxis
and dysphagia. The condition is caused by invasion of the wall
of one or both guttural pouches by Aspergillus spp. fungus,
which leads to damage of vital vascular and neurological
structures. Surgical treatments carry the highest and most
predictable success rates and involve occlusion of the
damaged blood vessels.
Further investigation into the causative agent is needed if
we are to understand why this normal inhabitant of the airway
becomes pathological in some horses, what the predisposing
factors are and to allow early diagnosis to more effectively
prevent fatal haemorrhage and the development of career and
life-threatening neurological derangements.
Acknowledgements
The author gratefully acknowledges the help of Dr Keith
Baptiste, Dr Jim Schumacher and Mr Justin Perkins in the
preparation of this article.
References
Baptiste, K.E. (2004) The mystery of guttural pouch mycosis: the paradox of advancing knowledge of a rare disease. Vet. J. 168 , 1-2.
Baptiste, K.E., Naylor. J.M., Bailey, J., Barbers, E.M., Post, K. and Thornhill, J. (2000) A function for guttural pouches in the horse.Nature 403 , 382-383.
Brandt, J.F. (1863) Bericht uber eine Abhandlung, Untersuchung der Gattung Hyrax in anatomischer und verwandtschaftlicherBeziehung. In: Bulletin of the Academy of Imperial Science, St. Petersberg. 5, 508-510.
Caron, J.P., Fretz, P.B., Bailey, J.V., Barber, S.M. and Hurtig, M.B. (1987) Balloon-tipped catheter arterial occlusion for prevention ofhaemorrhage caused by guttural pouch mycosis: 13 cases (1982?1985). J. Am. vet. med. Ass. 191 , 345-349.
Cheramie, H.S., Pleasant, R.S., Robertson, J.L., Moll, H.D., Freeman, D.E. and Carrig, C.B. (1999) Evaluation of a technique to occludethe internal carotid artery of horses. Vet. Surg. 28, 83-90.
Colles, C.M. and Cook, W.R. (1983) Carotid and cerebral angiography in the horse. Vet. Rec. 19, 442-428.
Cook, W.R. (1966) Guttural pouch mycosis. Vet. Rec. 78, 396-398.
Cook, W.R. (1968) The clinical features of guttural pouch mycosis in the horse. Vet. Rec. 83, 336-345.
Cook, W.R., Campbell, R.S.F. and Dawson, C. (1968) The pathology and aetiology of guttural pouch mycosis in the horse. Vet. Rec. 83, 422-428.
Dixon, P.M. and Rowlands, A.C. (1981) Atlanto-occipital joint infection associated with guttural pouch mycosis in a horse. Equine vet. J. 13, 260-262.
Ellenberger, W. and Baum, H. (1943) Handbuch der vergleichenden Anatomie der Haustiere. Springer, Berlin.
Fraser, F.C. and Purves, P.E. (1960) Hearing in Cetaceans. Bulletin of the British Museum (Natural History) 7, 1-140.
Freeman, D.E. (1999) Guttural pouch. In: Equine Surgery , 2nd edn., Eds: J.A. Auer and J.A. Stick, W.B. Saunders, Sydney. pp 372-392.
Fig 10: A contrast arteriogram obtained during surgery forembolisation coil placement. Several coils can be seen withinthe vessels proximal to the carotid trifurcation.
EQUINE VETERINARY EDUCATION / AE / november 2007