Pharynx: neoplasia in Horses (Equis) | Vetlexicon
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Pharynx: neoplasia

ISSN 2398-2977

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Synonym(s): Pharyngeal neoplasia

Introduction

  • Neoplasia of the pharynx is infrequently diagnosed in the horse.
  • Primary pharyngeal neoplasms are very rare.
  • Squamous cell carcinoma is the most commonly reported tumor. Lymphoma, mast cell tumor, chondroma, neuroendocrine tumor, fibrosarcoma and melanoma have also been reported.
  • Cause: most neoplastic conditions of the pharynx arise by extension from neoplasia of adjacent structures such as the oral cavity and sinus.
  • Signs: relate to size and location of tumor. May cause space-occupying effects within the airway, uni- or bilateral nasal discharge, respiratory noise, dysphagia.
  • Diagnosis: endoscopy, occasionally oral examination, biopsy.
  • Treatment: benign, local masses may be removed surgically, or via diathermy or laser excision/ablation. Malignant masses have limited options; occasionally intralesional chemotherapy may allow local control. Radiotherapy may be a potential treatment depending on the location of the lesion, but has very limited availability and is very expensive.
  • Prognosis: guarded, unless complete surgical excision is possible.

Presenting signs

  • Clinical signs depend on the size and location of the tumor.
  • Dysphagia may be present secondary to functional or space-occupying effects of the mass.
  • Malodorous nasal discharge Nose: nasal discharge, secondary to tissue necrosis.
  • Destruction of the palate may lead to oronasal fisulation and ingesta-stained nasal discharge.

Age predisposition

  • Appears to be more common in middle-aged and older horses, but very few cases reported in the literature.

Cost considerations

  • Treatment, where possible, is difficult and can be expensive, especially if radiotherapy is performed.

Special risks

  • If surgical resection is to be attempted or advanced imaging performed under general anaesthesia (CT/MRI), the space-occupying effects of the mass may reduce airflow and/or make intubation challenging.

Pathogenesis

Etiology

  • Squamous cell carcionoma is the most common tumor of the pharynx, and solitary lymphomas have also been reported.
  • Other tumors at this location are very rare.

Timecourse

  • Usually a gradual onset of clinical signs, but signs may not become apparent until late in the course of the disease.
  • If an oronasal fistula develops, progression to an ingesta-stained nasal discharge may be rapid.
  • Often present with a very large and untreatable mass; extensive infiltration of surrounding tissues and lymphatics may occur even if the mass itself appears to be well localized.

Diagnosis

Presenting problems

  • See Clinical signs below.

Client history

  • May have a sudden onset of ingesta-stained nasal discharge if an oronasal fistula develops.

Clinical signs

Diagnostic investigation

  • Oral examination.
  • Endoscopic examination:
    • Irregular, ulcerated mass.
    • Smooth, thickened structure.
  • Transendoscopic biopsy allows for histopathological examination; fine needle aspirate may be diagnostic if biopsy not possible. Histopathological and cytological features depend on the tumor type.
  • Head radiographs may be helpful to evaluate the extent of the disease:
    • Soft tissue structures are hard to interpret on head radiographs.
    • Precise location and origin of the mass may not be detectable on radiographs.
  • Ultrasonography may be useful but is usually limited by the presence of air-filled structures and bone in the region. May allow evaluation of local lymph nodes and aid fine needle aspiration of these structures.
  • Advanced imaging (CT/MRI) will allow evaluation of the extent of the lesion:
    • MRI Magnetic resonance imaging has much better soft tissue capability but requires general anesthesia.
    • CT Computed tomography will give less soft tissue detail than MRI but can be undertaken standing which allows a more complete evaluation of the lesion without the requirement for general anesthesia.

Confirmation of diagnosis

Discriminatory diagnostic features

  • Histopathology.

Definitive diagnostic features

  • Histopathology.
  • Immunohistochemistry to confirm diagnosis may be required in some cases.

Gross autopsy findings

  • Dependent upon tumor type.
  • The extent of the lesion is often not clear from initial diagnostic evaluation, and masses may be far more invasive than they appear due to the difficulty in effectively visualizing the region via endoscopic evaluation.

Histopathology findings

  • Dependent upon tumor type.

Differential diagnosis

  • Benign versus malignant lesions.

Treatment

Standard treatment

  • Benign, localized masses may be surgically removable.
  • Laser surgery or diathermy may be successful for the removal of accessible, benign, localized masses.
  • Radiotherapy Radiotherapy can be used to treat some tumors in this area and could be a definitive, ie curative, treatment, but requires advanced imaging and multiple general anesthetics.
  • Intralesional chemotherapy may afford local control of some tumors.
  • Usually the prognosis is very poor due to the aggressive nature of most pharyngeal neoplasms and the likelihood of metastasis at the point of diagnosis.

Prevention

Outcomes

Prognosis

  • Most pharyngeal neoplasms carry a very poor/hopeless prognosis due to their malignant behavior.
  • The prognosis for localized benign tumors is fair if they are accessible and amenable to treatment.

Reasons for treatment failure

  • Highly malignant lesions.
  • High chance of invasive and metastatic lesion.
  • Late diagnosis.
  • Difficult anatomical location.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Garrett K S (2012) Advances in diagnostic imaging of the larynx and pharynx. Equine Vet Educ 24 (1), 17-18 VetMedResource.
  • Jakesova V, Konar M, Gerber V, Brachelente H J & Tessier C (2008) Magnetic resonance imaging features of an extranodal T cell rich B cell lymphoma in the pharyngeal mucosa in a horse. Equine Vet Educ 20 (6), 289-293 VetMedResource.
  • Tyler R J & Fox R I (2003) Nasopharyngeal amelanotic melanoma in a gelding age 9 years. Equine Vet Educ 15 (1), 19-26 VetMedResource.
  • Kelly D (2003) Diagnostic problems in nasopharyngeal malignant amelanotic melanomas. Equine Vet Educ 15 (1), 25 WileyOnline.
  • Sullivan E K & Parente E J (2003) Disorders of the pharynx. Vet Clin North Am Equine Pract 19 (1), 157-267 VetMedResource.
  • Adams R, Calderwood-Mays M B & Peyton L C (1988) Malignant lymphoma in three horses with ulcerative pharyngitis. JAVMA 193 (6), 674-676 PubMed.
  • Lane J G (1985) Palatine lymphosarcoma in two horses. Equine Vet J 17 (6), 465-467 PubMed.
  • Schuh J C L (1983) Squamous cell carcinoma of the oral, pharyngeal and nasal mucosa in the horse. Vet Pathol 23 (2), 205-207 PubMed.

Other sources of information

  • Knottenbelt D C, Patterson-Kane J C & Snalune K L (2015) Clinical Equine Oncology. Elsevier, UK.