Canis ISSN: 2398-2942

Radiology: upper airways

Contributor(s): Fraser McConnell

Introduction

Overview

  • Radiography has limited value in assessment of dynamic disease of upper airways, eg laryngeal paralysis and soft palate disorders unless fluoroscopy available.
  • In most cases additional investigations, eg bronchoscopy and tracheal wash Transtracheal wash will be required for diagnosis.

Radiographic considerations
Larynx and trachea

  • The lateral projection is generally the most informative as the trachea and larynx are obscured by the spine on the VD projection.
  • The skyline projection of the thoracic inlet may be helpful in identifying tracheal collapse.
  • For evaluating cervical trachea and larynx the ET tube should be removed when exposure made as this will hinder evaluation and may result in displacement of the trachea mimicking a cervical mass.

Upper airways

  • The neck should be in a neutral position and head carefully padded to avoid rotation when evaluating the pharyngeal region.
  • Rotation will result in the soft palate appearing thickened.

Bronchi

  • Left lateral and DV projections allow best visualization of bronchi.
  • The lung fields provide an inherent contrast within the thorax - a high KVp, low mAs should be used to maximize the range of densities available of pulmonary radiographs.
    Use as short an exposure time as possible to minimize movement blur.
  • A grid is necessary if the depth of tissue is >10 cm.
  • Exposure is normally made at the point of maximal inspiration.
  • Expiratory films are occasionally useful to document small pneumothoraces, air trapping and bronchial and tracheal collapse.
  • Care should be taken to include the entire pulmonary field.

Restraint

  • Examination is normally performed under sedation but heavily sedated animals may have poor inspiratory volumes making it impossible to obtain a view of a truely inflated lung.
  • General anesthesia is required to obtain a true lateral projection of head and neck. The endotracheal tube often hinders evaluation as it distorts soft palate and laryngeal position - if possible it should be removed for exposure.
  • The VD projection should be avoided if there is a large volume of pleural fluid.
    Most dyspneic animals will lie quietly in sternal recumbency for a DV projection with minimal restraint and no sedation.Stressful handling of dyspneic animals may result in fatal decompensation.

Indications

Radiographic anatomy

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Interpretation

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Additional studies

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource and PubMed.
  • Carlisle C H, Biery D N & Thrall D E (1991) Tracheal and laryngeal tumors in the dog and cat - literature review & 13 additional patients. Vet Radiol 32, 1991.


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