Lateral and ventrodorsal radiographic views of both the skull and cervical areas are indicated. Radiopaque foreign bodies can be identified that may be missed on laryngoscopy and pharyngoscopy (e.g. sewing needle embedded in soft tissues). Radiographs are also useful in identifying bony changes associated with chronic inflammation or neoplasia, identifying clues of unreported trauma (e.g. subcutaneous emphysema), and occasionally soft tissue masses. Suggestion of a soft tissue mass is confirmed by direct visualization and histopathology. Thoracic radiographs are also indicated. Symptoms of lower respiratory disease may be masked when a patient has concurrent, and more severe, upper respiratory symptoms. Evaluation for aspiration pneumonia, metastases, or suggestion of a motility disorder (i.e. megaesophagus) is possible.
Ultrasonography and computed tomography (CT) are noninvasive modalities to evaluate the pharynx and larynx. Ultrasonography can identify soft tissue masses, help guide fine needle aspiration, and evaluate laryngeal function. The presence of air in these areas can limit the usefulness of this modality in establishing a definitive diagnosis. CT may be used to fully evaluate involvement of neoplasia or middle-ear disease if a nasopharyngeal polyp is suspected.
Videofluoroscopy is essential for any case of dysphagia. A barium swallow allows the act of swallowing to be recorded and studied for abnormalities. The patient should be recorded attempting to swallow barium to mimic liquids and then should be given a meal (canned food mixed with barium) to be recorded. Videofluoroscopy is superior to radiography because it allows all phases of deglutition to be evaluated instead of recording one moment (intermittent moments) of the event. Unfortunately videofluoroscopy is limited to referral centers only.
Pharyngoscopy and Laryngoscopy
Laryngoscopy and pharyngoscopy allow assessment of both structural abnormalities and function of the larynx. A flexible endoscope is used for these procedures because visualization of the nasopharynx requires retroflexion. Occasionally a foreign body will be found just caudal to the larynx and may be retrieved endoscopically. The patient is placed in sternal recumbency and anesthetized with either propofol or sodium thiopental. Once anesthetized, gauze is passed under the maxilla behind the canine teeth. The gauze is used to elevate the head, so external compression of the neck is avoided. Flexible endoscopy is ideal to evaluate the nasopharynx. If that is not possible, the caudal pharynx can be evaluated using a dental mirror and a snook hook. This will be sufficient in evaluating most nasopharyngeal polyps, masses, or caudal foreign bodies. It will not allow diagnosis of more rostral diseases such as nasopharyngeal stenosis. Laryngeal function is usually evaluated first by assessing the motion of the arytenoid cartilages. The traditional approach involves titrating anesthesia that allows both visualization of the arytenoid cartilages and deep spontaneous breaths to occur. In a normal animal the arytenoid cartilages will abduct symmetrically with each inspiration and close on expiration. The frustration with this technique is multiple. Maintaining the correct level of anesthesia is difficult (i.e. the animal is too awake to allow adequate visualization of the arytenoid cartilages or anesthetized so that the patient will not spontaneously breathe); shallow breathing can limit adequate assessment; and concerns about the effect of anesthesia on laryngeal function are legitimate concerns when performing the traditional laryngeal examination. The recently introduced technique attempts to eliminate the effects of anesthesia from the examination. Patients are premedicated with acepromazine maleate and butorphanol tartrate and induced with propofol. Doxapram hydrochloride (2.2 mg/kg intravenously) is used to increase laryngeal motion and minimize or eliminate the effects of anesthesia,
Hematology and biochemical profiles should be performed on patients with pharyngeal and laryngeal dysfunction, but they will rarely confirm the definitive diagnosis. Occasionally virus isolation (feline calicivirus (FCV)) and PCR (feline herpes-1 virus (FHV-1), Chlantydia spp. and Mycoplasma spp.) are indicated in the diagnostic workup. Culture and sensitivity of tissue or secretions can provide valuable information during the diagnostic workup. Cytology and histopathology are also essential for critically evaluating infiltrative disease or mass lesions.