Trachael collapse in an adult goat

A 9-year-old, mixed-breed, male goat was referred to the Veterinary Hospital of the Faculdade de Medicina Veterinária e Zootecnia of the Universidade de São Paulo, Brazil. The goat had been kept in a clean paddock, fed hay and concentrates, and dewormed periodically. The animal was first seen coughing and choking; then, within 10 min, it stood in decubitus, foaming at the mouth and cyanotic. At this point, it was decided to refer the animal to the university veterinary hospital, but it died during transportation. The following observations were made at necropsy: hydrothorax and hydropericardium; presence of foamy secretion in the cranial airways, including the nostrils; lungs with mild congestion, intense edema, and fibrotic areas; tracheal rings with a great distance between their dorsal edges without cartilage damage (Figure 1), corresponding to a tracheal collapse grade II (1), up to the bifurcation of the trachea.

Figure 1. Photograph of a caprine grade II tracheal collapse. Observe the displacement of the free edges of the cartilagenous rings.

Tracheal collapse or dorsoventral flattening is an airway obstruction (1,2); it should not be confounded with tracheal stenosis (3). It has been reported in calves, foals, dogs, cats, and humans (3,4,5,6). Only 1 case has been reported in goats: a 4-month-old kid with the collapse affecting the cervical region (7). The collapse is often associated with an ample, hypotonic, and pendulous dorsal membrane and to weak, poorly arched, cartilage arcs (4). In dogs, tracheal collapse involves either the cervical or the thoracic tracheal area (4). In calves, the caudal cervical and thoracic sections of the trachea are the most affected (5).

Many etiologies for tracheal collapse have been proposed: Congenital malformations, genetic- or nutrition-induced cartilagenous weakness, deficient innervation of the tracheal muscles, and primary disease of the caudal respiratory tract (3,6). In dogs and cats, tracheal collapse occurs in mid-aged and elderly animals; in cattle, the majority of cases occur in calves (4,6). The congenital form in dogs is associated with ring malformations (4). In the acquired collapse, there is no loss in ring diameter, but the rings lose their capacity to stay firm, so they collapse and become hypocellular with matrix variation (4). In calves, no abnormality was found at histological evaluation (5,6).

The collapse classification is based on the percentage of diminution of the tracheal lumen (1): Grade I (25% reduction), grade II (50%; pendulous membrane and relaxed cartilage), grade III (75%; membrane almost in contact with the ventral wall), and grade IV (lumen almost obliterated).

Typical clinical signs are cough, dyspnea, exercise intolerance, weight loss, retarded growth, tachycardia, tachypnea, and cyanosis (2,6,8). Affected animals may also be asymptomatic or have syncope episodes (1,2). Light exercise can induce severe dyspnea, cough, cyanosis, and decubitus, although the manifestations disappear after a short period. In the goat that was reported (7), chronic dyspnea and delayed growth were observed.

Diagnosis can be established by tracheal palpation, radiography, endoscopy, and fluoroscopy (2,4,6,8).

Treatment can be medical, surgical, or a combination of both, neither of which provides a cure but can attenuate the symptoms (1,2,4). External protheses have been used successfully in calves and in the 1 kid (6,7).

In this case, the initial diagnosis was asphyxia by a foreign body, which is common in the goat. Finding the collapsed trachea was unexpected, as this had not been suspected in an adult goat. The collapse was present throughout the trachea, similar to that described in mid-aged dogs, where the animals may be asymptomatic during most of their life (4). There was no cartilage deformation, as observed in elderly dogs (4), but a reduction in the tracheal lumen by a displacement of the free edges of the cartilagenous rings and an ample and pendulous dorsal membrane. According to the criteria used for dogs (1), the collapse in this goat was classified as grade II.

The animal had never presented respiratory signs until it suffered what, in dogs, is called “respiratory distress syndrome,” with cough progressing to severe dyspnea and cyanosis (4). Contrary to what is suggested for cattle, where tracheal collapse (by mechanic irritation and more mucus production) magnifies the risk of caudal airways disease (9), in this case, the pneumonia likely preceded the collapse and contributed to it, because of the major respiratory effort imposed to the animal (3,10). Macroscopic examination of the trachea did not show significant deformity of the tracheal rings, suggesting that the alterations were more related to an increased respiratory stress than to a congenital loosening of the cartilage (10). Death may have been the consequence of the bronchopneumonia-tracheal collapse associated with pulmonary edema.

It is possible that the collapse preceded the pneumonia, but this could only have been confirmed through histological examination of the tracheal cartilage, which, unfortunately, could not be performed.

The importance of this report is that it is the 2nd published report of tracheal collapse in the goat, establishing 1 more differential diagnosis in cases of severe dyspnea and cyanosis in this species.