Lower respiratory tract endoscopy in the cat: diagnostic approach to bronchial disease

Abstract

Practical relevance: Respiratory endoscopy is a useful diagnostic tool to evaluate the airways for the presence of mass lesions or foreign material while allowing for sample collection for cytologic and microbiologic assessment. While bronchial disease (eosinophilic or neutrophilic) is the most common lower respiratory disease identified in cats, infectious, anomalous and neoplastic conditions can clinically mimic inflammatory bronchial disease. Diagnostic imaging is unable to define the etiology for clinical signs of cough, tachypnea or respiratory difficulty, necessitating visual evaluation and collection of airway samples. Endoscopy allows intervention that can be life-saving and also confirmation of disease, which is important given that life-long medication is likely to be required for management of inflammatory airway disease.

Patient group: Cats with either airway or pulmonary disease benefit from laryngoscopy, tracheoscopy and bronchoscopy to determine an etiologic diagnosis. In the best situation, animals that require these procedures present early in the course of disease before clinical decompensation precludes anesthetic intervention. However, in some instances, these tests must be performed in unstable cats, which heightens the risk of the procedure. Cats that do not respond to empiric medical therapy can also benefit from bronchoscopic evaluation.

Clinical challenges: Due to the small size of feline airways and the tendency for cats to develop laryngospasm, passage of endoscopic equipment can be difficult. Bronchoconstriction can lead to hemoglobin desaturation with oxygen and respiratory compromise.

Evidence base: This article reviews published studies and case reports pertaining to the diagnostic approach to feline respiratory disease, focusing specifically on endoscopic examination of the lower airways in cats. It also discusses appropriate case selection, equipment, endoscopic techniques and visual findings based primarily on the authors' experiences.

Figure 1

The outer diameter of scopes used for feline bronchoscopy and laryngoscopy ranges from 2.5–4.0 mm. This image shows flexible endoscopes with an outer diameter ranging from 2.5–5.0 mm

Figure 2

A variety of instruments are available for bronchoscopic procedures. Generally the outer diameter of the instrument must be 0.2 mm less than the instrument channel of the scope to safely pass the length. Pictured here are 1.8 mm instruments: (a) loop snare, (b) retrieval forceps without spike (spiked forceps are useful for biopsy), (c) three-pronged grabber, (d) Wang needle and (e) guarded microbiology brush (unguarded cytology brushes are also available). Many of these instruments are also available in 1.0 mm diameter for smaller scopes with a 1.2 mm channel

Figure 3

Suction trap used for collecting BAL samples

Figure 4

Laryngoscopy images showing a normal feline larynx (a) with a jet ventilator catheter traversing the laryngeal opening and (b) an obstructive carcinoma

Figure 5

Illustration of the feline bronchial tree. Courtesy of Dr Roberta Caccamo

Figure 6

Bronchoscopic images showing a combination of gross findings including (a) airway collapse, (b) stenosis, (c) hyperemia and (d) mucus plugging. Unfortunately, gross findings correlate poorly with cytologic or histopathologic diagnoses

Figure 7

Endobronchial neoplasia is rarely identified in the cat. This is an image of a tracheal adenocarcinoma prior to debulking using an endoscopic snare. A catheter used for jet ventilation is in the foreground

Figure 8

Piece of gravel found within the trachea of a cat, which was removed using a three-prong grabber and basket retrieval forceps

Figure 9

Suppurative inflammation is characterized by either degenerate or non-degenerate neutrophils and is consistent with infectious or inflammatory airway disease. Such samples should be carefully scrutinized for the presence of organisms, although Mycoplasma species are rarely identified cytologically due to lack of a cell wall

Figure 10

Eosinophils can make up to 20% of normal BAL cytology in the cat. Excessive eosinophils (>20%) are suggestive of asthma or inflammatory airway disease