Primary Tracheal Collapse in a Cat

CT measurements of tracheal diameter and length in normocephalic cats

OBJECTIVES

The aim of this study was to measure the tracheal dimensions of normocephalic cats using CT.

METHODS

CT images of 15 client-owned normocephalic cats were retrospectively evaluated to measure the length of the feline trachea. Transverse and vertical inner diameters were measured in five different tracheal regions, and the cross-sectional area of the tracheal lumen was calculated for each point of measurement. Descriptive statistics were applied using a two-tailed t-test.

RESULTS

The mean ± SD length of the trachea was 125.13 ± 14.41 mm. Male cats had significantly larger tracheas than female cats. The transverse diameter first increased by 0.94 mm between the most cranial point of measurement and the middle of the trachea. It then decreased by 1.38 mm between the middle of the trachea and the most caudal point of measurement. The vertical diameter decreased by 1.16 mm between the first point of measurement and the penultimate point, and then increased by 0.06 mm between the penultimate point of measurement and the end of the trachea. The two different diameters resulted in an elliptical trachea shape.

CONCLUSIONS AND RELEVANCE

The feline trachea was circular only at its cranial and caudal ends, and elliptical with a dorsoventral flattening along the rest of its length. Vertical and transverse diameters varied along the entire length. Tracheal shape differences should be considered when performing permanent tracheostomy, tracheal anastomosis or stenting in cats.

Self-expanding tracheal stent placement in a cat with primary tracheal collapse

A 12-year-old mixed-breed spayed female cat presented with dyspnoea, open-mouthed breathing, and cyanosis that was difficult to control with medical pharmacotherapy; the cat was diagnosed with the primary tracheal collapse of the neck and chest regions. The diagnosis was confirmed by dynamic chest radiography, tracheal endoscopy, and computed tomography (CT). Tracheal endoscopy and CT showed dropsy of the dorsal membranous wall over most of the trachea. A self-expanding Nitinol cross-and-hook braided stent was placed along the entire tracheal lumen using surgical X-ray fluoroscopy. Bacterial cultures in the trachea were negative. Dyspnoea disappeared immediately after the endotracheal stent was implanted. Although the long-term prognosis remains under observation, the short- to medium-term prognosis was very good. These results suggest that stenting may be useful in the treatment of primary tracheal collapse in cats.

Radiographic evaluation of tracheal collapse in dogs by compressive technique

ABSTRACT The purpose of this study was to verify the applicability of the compressive radiographic technique (pressures of 5, 10, 15 and 20mmHg) in the diagnosis of tracheal collapse in small breed dogs, in lateral cervicothoracic radiography. Out of the 50 dogs evaluated, 25 presented tracheal collapse (TG group), 23 did not present tracheal collapse (CG) and two were excluded because they did not tolerate a pressure of 20 mmHg. The TG group presented a smaller internal diameter of the trachea in the region of the fourth cervical vertebra (D4) and at the entrance of the thorax (TDE) compared to the CG group, in all the radiographic projections performed, as well as within the TG group where the compressive technique differed from conventional. Furthermore, there was a correlation between the clinical sign of coughing during cervical collar use and the presence of radiographic tracheal collapse at a pressure of 20 mmHg. It was concluded that the compressive radiographic technique was feasible and efficient in confirming the diagnosis of tracheal collapse in dogs, especially in the pressure of 20 mmHg, where it was associated with clinical signs, and can be used in isolation or complementary to the conventional technique.

Lower respiratory tract endoscopy in the cat

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.

Radiographic measurements of the trachea in domestic shorthair and Persian cats

Tracheal diameter can be assessed from a thoracic radiograph, with assessment of tracheal diameter in dogs based on ratios between tracheal diameter and a skeletal measurement. Reference intervals are not, however, available for the cat. Tracheal narrowing may cause significant clinical problems, although tracheal hypoplasia in dogs may be clinically silent, and is rarely reported in cats (both mesati- and brachycephalic). The tracheal diameter and trachea:thoracic inlet and trachea:rib ratios were calculated for populations of domestic shorthair (DSH) (n = 68) and Persian (n = 40) cats. This gave reference intervals for radiographic tracheal measurements in these breeds. It is proposed that the tracheal diameter in a normal DSH cat should be 18% of the diameter of the thoracic inlet, and compared to 20% in Persian cats.