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Pharynx: 4th branchial arch defects
Synonym(s): RDPA, cricopharyngeal-laryngeal dysplasia, palatopharyngeal arch displacement (rostral
Introduction
- Cause: a congenital defect causes failure of development of derivatives of 4th branchial arch which make up components of the larynx and pharynx.
- Results in unilateral or bilateral hypo- or aplasia of the wings of the thyroid cartilage, cricothyroid articulations, cricothyroideus and cricopharyngeus muscles.
- Signs: vary depending on the severity of the deformity, ranging from respiratory obstruction and dysphagia to poor performance at exercise.
- Diagnosis: history, signs, endoscopy, radiography.
- Treatment: none.
- Prognosis: depends on severity of condition - generally poor for athletic function.
Geographic incidence
- Worldwide.
Age predisposition
- Congenital deformity.
- Severely affected individuals with marked clinical signs may be diagnosed at an early age.
- Less severely affected individuals may be diagnosed during routine endoscopic examination at yearling sales or detected once training begins or progresses.
Breed/Species predisposition
- 0.3% in Thoroughbreds Thoroughbred .
- Found in other breeds such as Hanoverian Hanoverian , Warmbloods Dutch warmblood and Haflingers Haflinger .
Cost considerations
- Economic loss - generally do not make athletes.
- Cost due secondary colic and inhalational pneumonia which may necessitate euthansia Euthanasia .
Pathogenesis
Etiology
- Congenital.
Specific
- Failure of some or all of the derivatives of 4th branchial arch (unilaterally or bilaterally) to develop normally.
- These structures include wings of the thyroid cartilage, cricothyroid articulations, cricothyroideus and cricopharyngeus muscles.
Pathophysiology
- Derivatives of 4th branchial arch are hypo- or aplastic.
- No stable structure between wing of thyroid and cricoid cartilages → failure to provide intrinsic support for the musculature of the larynx → defective arytenoid motility.
- Absence of cricopharyngeal muscle which is part of the rostral esophageal sphincter → inability to close upper esophageal sphincter → involuntary aerophagia.
- There is no means by which the palatal pillars can be anchored into a position caudal to the apices of the corniculate cartilages → rostral displacement of the pharyngeal arch (RDPA).
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
- Smith L J & Mair T S (2009) Fourth branchial arch defect in a Welsh section A pony mare. Equine Vet J 41 (6), 366-364 VetMedResource.
- Blickslager A T, Tate L P & Tudor R (1999) Transendoscopic laser treatment of rostral displacement of the palatopharyngeal arch in four horses. J Clin Laser Med Surg 17 (2), 49-52 PubMed.
- Gaughan E M & DeBowes R M (1993) Congenital diseases of the equine head. Vet Clin North Am Equine Pract 9 (1), 93-110 PubMed.
- Dixon P M, McGorum B C & Else R W (1993) Cricopharyngeal-laryngeal dysplasia in a horse with sudden clinical onset idiopathic laryngeal hemiparesis. New Zealand Vet J 41(3), 134-138 PubMed.
- Goulden B E, Anderson L J, Davies A S & Barnes G R G (1976) Rostral displacement of the palatopharyngeal arch: a case report. Equine Vet J 8 (3), 95-98 PubMed.
Other sources of information
- Lane J G (1993) Fourth Brachial Arch Defects. In: Proc Bain Fallon Memorial Lecture. Canberra, Australia.