A4-month-old 127.5-kg (280.5-lb) Holstein heifer calf (patient 1) was referred to University of Wisconsin Veterinary Care for evaluation of dyspnea and wheezing that had persisted for 2 months despite antimicrobial and anti-inflammatory treatment (drugs and dosages unknown). Other pertinent history included the fact that the calf was born with the assistance of forced extraction owing to a posterior presentation.
During the initial examination at the referral hospital, the calf was quiet but alert and responsive. The calf was slightly hyperthermic (rectal temperature, 39.3°C [102.8°F]; reference range, 38.0°C to 39.17°C [100.4°F to 102.5°F]), tachycardic (heart rate, 100 beats/min; reference range, 60 to 84 beats/min), and tachypneic (respiratory rate, 40 breaths/min; reference range, 10 to 30 breaths/min). It had increased inspiratory effort and stridor, and coughing was elicited by tracheal palpation. On thoracic auscultation, upper airway (tracheal) sounds were referred over the thoracic cavity. A soft tissue mass was palpable at the caudoventral aspect of the neck just cranial to the thoracic inlet. Results of a CBC and serum biochemical analysis were unremarkable.
Thoracic radiographs were obtained. Lateral radiographic images indicated severe dorsoventral narrowing of the tracheal lumen. The narrowing was most severe at the level of the thoracic inlet (Figure 1). The tracheal lumen appeared to return to its normal diameter caudal to the stenotic region at the level of the first intercostal space. The lung field had a mild diffuse bronchial and unstructured interstitial pattern suggestive of mild interstitial pneumonia, bronchopneumonia, or an expiration artifact. A well-circumscribed, semicircular, soft tissue or fluid-opaque mass that measured approximately 20 × 8 cm was located ventral to the trachea and extended from the midcervical region to the thoracic inlet. Differential diagnoses for the mass included thymus, enlarged cervical lymph node, abscess, and hematoma. Nasotracheal endoscopy confirmed that the trachea became stenotic approximately 70 cm distal to the nares (Figure 2).
Right lateral radiographic image of the cranial portion of the thorax of a 4-month old 127.5-kg (280.5-lb) Holstein heifer calf that was examined because of dyspnea and wheezing of 2 months’ duration that did not respond to antimicrobial and anti-inflammatory treatment (patient 1). Notice that there is severe dorsoventral narrowing of the tracheal lumen (arrows) at the level of the thoracic inlet and a well-circumscribed, semicircular, soft tissue or fluid-opaque mass (star) ventral to the trachea that extends from the midcervical region to the thoracic inlet.
Citation: Journal of the American Veterinary Medical Association 257, 10; 10.2460/javma.2020.257.10.1051
Endoscopic image of the tracheal lumen of the calf of Figure 1 obtained approximately 70 cm distal to the nares at the level of the thoracic inlet. Notice that the tracheal lumen appears narrow and ellipsoidal in shape. Ventral is to the right of the image.
Citation: Journal of the American Veterinary Medical Association 257, 10; 10.2460/javma.2020.257.10.1051
Computed tomography was performed to obtain specific measurements of the stenotic region of the trachea for potential stent development. The CT sequences revealed that the caudal aspect of the cervical portion of the trachea gradually narrowed dorsoventrally until it reached the level of the thoracic inlet. The intraluminal area of the trachea at the thoracic inlet was > 80% less than that at the cranial aspect of the cervical portion of the trachea (Figure 3). Caudal to the thoracic inlet, the intrathoracic portion of the trachea gradually expanded but remained ellipsoidal in shape until it reached the carina. The abnormally narrowed portion of the trachea was 16.8 cm in length and extended from the caudal aspect of the cervical portion of the trachea to immediately cranial to the carina. The most severely narrowed portion of the trachea was approximately 4.5 cm in length and was located in the region of the thoracic inlet. Mineral-attenuating calluses with smooth margins were identified bilaterally within the midbody of the first and second ribs and measured 3 cm at their widest points. Progressively smaller calluses were located within the midbody of the third to sixth rib pairs. The callus on the left first rib appeared to be in contact with but did not deviate the trachea. The distal aspects of the left and right first ribs were axially displaced into the thoracic cavity, the right rib more so than the left rib. The soft tissue mass immediately cranial to the thoracic inlet measured 5.6 × 7.0 × 15 cm and caused minimal dorsal displacement of the adjacent portion of the trachea. While the calf was still sedated after completion of the CT evaluation, a fine-needle aspirate specimen was obtained from the mass and submitted for cytologic evaluation. Cytologic evaluation of the specimen revealed lymphoid tissue with frequent sheets of ciliated respiratory epithelial cells, which was most consistent with a bronchial cyst.
Transverse CT images of the thorax of the calf of Figure 1 obtained at the level where the tracheal lumen (arrow) was at its smallest diameter (0.44 cm; A) and at the level of the first rib (B). In panel B, notice that the bony callus (star) on the left first rib appears to be in contact with the trachea. The right side of the calf is to the left in both images.
Citation: Journal of the American Veterinary Medical Association 257, 10; 10.2460/javma.2020.257.10.1051
Tracheal collapse and stenosis secondary to perinatal rib fractures were diagnosed on the basis of clinical and diagnostic imaging findings. Initially, the owner agreed to pursue endoscopic placement of a stent within the lumen of the stenotic portion of the trachea. The calf was discharged from the hospital and sent home until a stent could be custom manufactured. It was recommended that the calf be individually housed in a cool, dry, well-ventilated stall in an environment with little dust and no access to headlocks or stanchions.
The calf's dyspnea became less apparent at home over the subsequent 4 to 6 weeks, and the owner decided to forego stent placement. The calf's growth appeared to be unaffected by the condition because it remained comparable in size to similarly aged herdmates.
Patient 1 became a productive oocyte donor after reaching sexual maturity and was returned to the referral hospital for follow-up diagnostic imaging at 21 months old. At that time, the patient was 6 months pregnant and was bright, alert, and active with a body condition score of 4/5 (Figure 4). On physical examination, rectal temperature (38.7°C [101.6°F]), heart rate (60 beats/min), and respiratory rate (24 breaths/min) were all within the respective reference ranges. Tracheal and thoracic auscultation revealed no abnormalities. The soft tissue mass in the caudal cervical region was no longer palpable, and no other remarkable findings were identified.
Photograph of patient 1 from Figure 1 at 21 months old (ie, 17 months after diagnosis of tracheal collapse and stenosis secondary to perinatal rib fracture). The patient was of normal size and 6 months pregnant at the time this photograph was obtained.
Citation: Journal of the American Veterinary Medical Association 257, 10; 10.2460/javma.2020.257.10.1051
Radiographs of the caudal portion of the cervical region and thorax were obtained. Evaluation of the radiographic images revealed no overt evidence of a collapsing trachea and no other abnormal findings (Figure 5). Remarkably, the tracheal stenosis had resolved, and there was no appreciable narrowing of the tracheal lumen between the midcervical region and carina.
Left lateral radiographic image of the cranial aspect of the thorax of the heifer of Figure 4. Notice that the tracheal lumen (arrows) no longer appears stenotic in the region of the thoracic inlet.
Citation: Journal of the American Veterinary Medical Association 257, 10; 10.2460/javma.2020.257.10.1051
During nasotracheal endoscopy, a slight linear mucosal defect that occupied < 20% of the tracheal circumference was observed in the dorsal lining of the trachea approximately 80 to 90 cm distal to the nares (Figure 6). The tracheal stenosis was deemed resolved. Since that time, patient 1 has calved and has become a productive member of the herd.
Endoscopic image of the tracheal lumen of the heifer of Figure 4 obtained at the level of the thoracic inlet (ie, at approx the same level as the image in Figure 2). Notice that there is a slight linear corrugated-appearing defect in the dorsal aspect of the tracheal mucosa that extends from approximately the 12 to 1 o'clock positions. Ventral is to the bottom of the image.
Citation: Journal of the American Veterinary Medical Association 257, 10; 10.2460/javma.2020.257.10.1051
A 4-month-old 174-kg (382.8-lb) Holstein bull calf (patient 2) was referred to University of Wisconsin Veterinary Care for evaluation of persistent cough and dyspnea that had persisted for 3 months despite antimicrobial and anti-inflammatory treatment (drugs and dosages unknown). The calf had no history of trauma, and its birth was not witnessed.
During the initial physical examination at the referral hospital, the calf was bright, alert, and responsive. The calf was euthermic (rectal temperature, 39°C [102.2°F]), tachycardic (heart rate, 130 beats/min), and tachypneic (respiratory rate, 60 breaths/min), with increased inspiratory effort and stridor. The calf had an occasional cough that was honking in nature. On thoracic auscultation, sounds from the upper airway (trachea) were referred over the thoracic cavity, which made it challenging to hear air movement within the lower airways. Results of a CBC and serum biochemical analysis were unremarkable.
Thoracic radiographs were obtained. The right lateral radiographic image indicated a marked narrowing of the trachea from the level of C6 to the thoracic inlet (Figure 7). The left first, second, and third ribs were misshapen, compared with their contralateral counterparts. For each of the left first, second, and third ribs, the midbody had a smoothly marginated fusiform widening and the distal aspect had an abnormal curve in the cranial direction.
Right lateral radiographic image of the cranial portion of the thorax of a 4-month-old 174-kg (382.8-lb) Holstein bull calf that was examined because of a persistent cough and dyspnea of 3 months’ duration that did not respond to antimicrobial and anti-inflammatory treatment (patient 2). Notice the marked ventrodorsal narrowing of the trachea that extends from the level of C6 to the thoracic inlet (arrows). There is also bony callus formation at the midbody of the left first and second ribs (stars).
Citation: Journal of the American Veterinary Medical Association 257, 10; 10.2460/javma.2020.257.10.1051
Similar to patient 1, CT was performed to obtain specific measurements of the stenotic region of the trachea for potential stent development. The CT sequences confirmed marked dorsoventral narrowing of the trachea, with a > 90% reduction in the diameter of the intratracheal lumen at the level of the thoracic inlet (Figure 8). Overall, an 11.3-cm portion of the trachea was abnormally narrowed, with the most severely narrowed portion measuring approximately 4.6 cm in length. Nothing within the mediastinum appeared to be compressing the trachea. There was axial deviation and mild flaring of the midbody region, albeit with smooth cortical margins, of the cranial aspects of the left first, second, and third ribs. Given the clinical and diagnostic imaging findings, the diagnosis was tracheal stenosis and collapse secondary to perinatal rib fractures.
Transverse CT image of the thorax of the calf of Figure 7 obtained at the level where the tracheal lumen (arrow) was at its smallest diameter (0.39 cm) near the level of the thoracic inlet. The right side of the calf is to the left of the image.
Citation: Journal of the American Veterinary Medical Association 257, 10; 10.2460/javma.2020.257.10.1051
Because the calf appeared to be systemically healthy with only an occasional cough and dyspnea, it was discharged from the hospital and sent home for conservative treatment. It was recommended that the calf be individually housed in a cool, well-ventilated environment with little dust.
The calf was subsequently acquired by and moved to a commercial bull stud facility. Similar to patient 1, patient 2's clinical signs resolved over time without further intervention. Patient 2 was reexamined at 26 months of age for the purpose of the present report. At that time, patient 2 weighed approximately 818 kg (1,800 lb) and had a satisfactory body condition. Physical examination findings were unremarkable with no abnormalities detected during tracheal and thoracic auscultation. A nasotracheal endoscopic examination was performed with a 3-m endoscope,a which allowed the entire length of the trachea to be evaluated to the carina. The trachea appeared clinically normal throughout its entire length (Figure 9), and it was determined that the tracheal stenosis had resolved.
Endoscopic image of the tracheal lumen of the bull described in Figure 7 obtained at the level of the thoracic inlet when the patient was 26 months old (ie, 22 months after diagnosis of tracheal collapse and stenosis secondary to perinatal rib fracture). Notice that there is a slight linear corrugated-appearing defect in the dorsal aspect of the tracheal mucosa at approximately the 12 o'clock position. Ventral is to the bottom of the image.
Citation: Journal of the American Veterinary Medical Association 257, 10; 10.2460/javma.2020.257.10.1051
The bull stud facility began collecting semen from patient 2 when the bull achieved sexual maturity. Patient 2 remains a productive member of the bull stud facility and has hundreds of progeny within the Holstein breed.
Discussion
Reports of tracheal collapse in dairy calves are rare.1–5 Rib fractures associated with dystocia have been proposed as an etiology for tracheal collapse in large animals2 and have been commonly associated with the problem in cattle.1,3,6 During dystocia, compression of the thoracic cavity can injure the tracheal rings at the thoracic inlet and fracture ribs.6 Although tracheal rings have an elastic nature, rings that have been compressed are often less rigid and may have a tendency to malform.6 As calves with fractured ribs age, callus formation at the fracture sites can compress the trachea at the thoracic inlet.6 Additionally, in calves, the thoracic portion of the trachea may weaken secondary to an increase in negative pressure owing to the dynamic events of inspiration.6 Congenital or hereditary defects, although difficult to definitively diagnose, may also play a role in the pathogenesis of tracheal collapse and stenosis in calves. If tracheal collapse is the result of a hereditary condition, treatment of affected animals so that they can be raised for breeding purposes has ethical considerations.
In calves, clinical signs associated with tracheal collapse often include a honking cough, wheezing, dyspnea, tachypnea, tachycardia, exercise intolerance, and stunted growth.1,3,7 Other more common differential diagnoses for calves with those clinical signs include necrotic laryngitis, pharyngeal collapse, intratracheal foreign body, or extratracheal compression.8 Tracheal collapse can be difficult to definitively diagnose without diagnostic imaging, such as thoracic radiography or nasotracheal endoscopy. The ready availability of portable radiographic units makes diagnosis of tracheal collapse in calves possible in field situations because lateral radiographic images that include the thoracic inlet can be easily obtained and provide valuable information about the trachea as well as the extent of lower airway disease. Tracheal collapse should be considered a differential diagnosis for calves with progressive inspiratory dyspnea subsequent to dystocia or palpably enlarged costochondral junctions.6
For calves with tracheal collapse, treatment with antimicrobials, corticosteroids, and tracheotomy is generally ineffective.8 Placement of prostheses, or stents, in the collapsed portion of the trachea has been attempted with variable efficacy,1,6 and prostheses may need to be removed or replaced to avoid complications.1 It is estimated that surgical placement of a stent within the stenotic portion of the trachea is successful in ≤ 30% of treated calves.6 Although stent placement may improve the animal's condition in the short term, the tracheal diameter is permanently limited by the size of the stent used.6 Additionally, if more than the most cranial aspect of the thoracic portion of the trachea is damaged, surgical access to the affected segment becomes more difficult and perhaps impossible.6 Alternatively, in a 2016 report,7 2 of 3 Japanese Black calves with tracheal collapse and stenosis secondary to perinatal rib fractures were successfully treated by partial costectomy with and without balloon dilation of the stenotic portion of the trachea. The prognosis for calves with tracheal collapse is dependent on the severity and location of the collapse as well as the extent of lower airway disease. However, most calves with tracheal collapse and stenosis are given a guarded prognosis and are euthanized or managed until slaughtered.
The present report described 2 Holstein calves with tracheal collapse and stenosis secondary to perinatal rib fractures that fully recovered without surgical intervention. The outcomes for the 2 calves of this report suggested that perinatally acquired tracheal stenosis can resolve with no or only conservative treatment over the first 2 years of life. We believe that the positive outcomes for these 2 calves were the result of early identification of tracheal collapse as the cause of dyspnea rather than disease affecting the lower airways and appropriate subsequent management that prevented the development of pneumonia. Given the positive outcome for these 2 calves, it appears that the trachea in young calves is capable of considerable healing and natural reconstructive growth, which may obviate the need for surgery in animals with perinatal tracheal collapse and stenosis.
To our knowledge, the present report was the first to describe natural resolution of tracheal collapse and stenosis secondary to perinatal rib fractures in calves, with the calves subsequently achieving phenotypic maturity and becoming reproductively sound. Previous reports1,6,7 of calves with tracheal collapse that underwent surgical intervention suggest that the condition has a guarded prognosis. Some calves of those reports1,6,7 survived and gained sufficient weight to become marketable for beef production, but many died of bronchopneumonia or were sold or euthanized because of poor growth and performance.1,7 Moreover, the tracheal diameter following surgical intervention for alleviation of tracheal collapse is limited by the constraints of the prosthesis used.1,6
Both calves of the present report originated from well-managed herds and had high genetic value. We believe that the high level of herd management and veterinary involvement at the facilities of origin as well as the individual care received by the calves played important roles in the positive outcomes for both animals. The calves were individually housed in pens in a cool and well-ventilated environment year-round. They were not forced to compete with herdmates and were not required to use headlocks. Those factors likely prevented the calves from developing pneumonia and contributed to the successful outcomes. Although these 2 calves provided evidence that the bovine trachea is capable of substantial repair and remodeling over the long term, the severity of their clinical signs suggested that calves with tracheal collapse are compromised and at high risk for developing further respiratory tract disease.
We can only speculate as to the factors that contributed to the positive outcomes for the 2 calves of the present report. Neither calf had substantial lower airway disease at the time of initial examination at the referral hospital, and owing to excellent management, neither calf subsequently developed bronchopneumonia. Other important factors to consider are the length of the collapsed or stenotic portion of the trachea and the extent to which callus formation on healing rib fractures impinges on the diameter of the thoracic inlet. The veterinary literature contains no information regarding how the length of the abnormal portion of the trachea affects prognosis, but it seems plausible to expect that prognosis would become worse as the length of the affected portion of the trachea increases.
The present report described positive outcomes for 2 Holstein calves with tracheal collapse and stenosis secondary to perinatal rib fractures that were managed conservatively by individual housing in cool, well-ventilated stalls without access to headlocks. Both calves grew as expected, achieved reproductive maturity, and became productive members of the breed. These calves provided evidence that tracheal collapse secondary to perinatal rib fracture may resolve over time as long as lower airway disease is mild or absent, and similarly affected calves should not be euthanized if surgery is not an option owing to financial or other constraints. Further investigation of calves with tracheal collapse secondary to perinatal rib fracture is necessary to determine whether factors such as the size (length and diameter) of the affected trachea contribute to the likelihood of a favorable outcome in the absence of surgery.
Acknowledgments
The authors thank Dr. Jeff Bleck of Dairy Doctors, Plymouth, Wis, for assistance with management and follow-up for patient 1, and Chris Kortes of Karl Storz Veterinary Endoscopy, Goleta, Calif, for technical assistance with the portable endoscopic equipment used to acquire the follow-up endoscopic images for patient 2.
ABBREVIATIONS
| JSEPM | Japanese Society of Exotic Pet Medicine |
Footnotes
Karl Storz Veterinary Endoscopy, Goleta, Calif.
References
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