Page 301 - Small Animal Internal Medicine, 6th Edition

CHAPTER 17
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Diagnostic Tests for the

Larynx and Pharynx

RADIOGRAPHY rather than active muscle contraction (see Laryngoscopy and
Pharyngoscopy later in this chapter). Localization of mass
Radiographs of the pharynx and larynx should be evaluated lesions and guidance of needle aspiration of abnormal tissue
in animals with suspected upper airway disease (Figs. 17.1 or enlarged regional lymph nodes can provide a diagnosis in
and 17.2). Radiographs are particularly useful in identifying some cases.
radiodense foreign bodies such as needles, which can be
embedded in tissues, external compression of the airways,
and adjacent bony changes. It may not be possible to identify FLUOROSCOPY
or characterize these types of lesions with laryngoscopy
alone. Intraluminal soft tissue masses and soft palate abnor- In some patients, signs of upper airway obstruction occur
malities may also be seen. only during labored breathing. A diagnosis may be missed if
A lateral view of the larynx, caudal nasopharynx, and adequate breathing efforts do not occur during routine radi-
cranial cervical trachea is usually obtained. The vertebral ography or during visual examination under anesthesia. In
column interferes with airway evaluation on dorsoventral or these cases, fluoroscopic evaluation during signs of airway
ventrodorsal projections. Care must be taken to assure excel- obstruction, or audible sounds (stertor or stridor), can be
lent positioning of the head. Normal structures can appear invaluable. Unusual diagnoses, such as epiglottic retrover-
to be abnormal (e.g., masses, palate abnormalities) if there is sion and collapse of the dorsal pharyngeal wall, may not be
any rotation of the head and neck. The head should be held possible by other means. Extrathoracic tracheal collapse, a
with the neck slightly extended. Padding under the neck and differential diagnosis for upper airway obstruction due to
around the head may be needed to avoid rotation, but it pharyngeal or laryngeal disease, can often be diagnosed
should not distort the anatomic structures. Good position- as well.
ing of radiographs can be assessed by the superimposition of
the left and right osseous bullae, mandibles, and frontal
sinuses. Regardless, abnormal soft tissue opacities or nar- COMPUTED TOMOGRAPHY AND
rowing of the airway lumen identified radiographically must MAGNETIC RESONANCE IMAGING
be confirmed with laryngoscopy, endoscopy and/or com-
puted tomography, and biopsy. Laryngeal paralysis cannot Computed tomography and magnetic resonance imaging are
be detected radiographically. sensitive modalities for identifying masses that result in
external compression of the larynx or pharynx. Extent of
involvement and size of local lymph nodes can be assessed
ULTRASONOGRAPHY for patients with mass lesions external to or within the
airway.
Ultrasonography provides another noninvasive imaging
modality for evaluating the pharynx and larynx. Report-
edly laryngeal motion can be assessed (Rudorf et al., 2001). LARYNGOSCOPY AND
Because air interferes with sound waves, accurate assessment PHARYNGOSCOPY
of this area can be difficult. Experience is necessary to avoid
misdiagnosis, particularly with respect to laryngeal motion Laryngoscopy and pharyngoscopy allow visualization
as it can be the result of passive, paradoxical movement of the larynx and pharynx for assessment of structural

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