Equis ISSN 2398-2977

Pharynx: 4th branchial arch defects

Synonym(s): RDPA, cricopharyngeal-laryngeal dysplasia, palatopharyngeal arch displacement (rostral

Contributor(s): Debbie Archer, Christopher Brown, Paddy Dixon

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.

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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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 J41(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 Surg17(2), 49-52 PubMed.
  • Gaughan E M & DeBowes R M (1993)Congenital diseases of the equine head.Vet Clin North Am Equine Pract9(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 J41(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 J8(3), 95-98 PubMed.

Other sources of information

  • Lane J G (1993)Fourth Brachial Arch Defects.In:Proc Bain Fallon Memorial Lecture.Canberra, Australia.


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