History
An indoor-only 12-year-old 4.0-kg castrated male domestic shorthair cat was evaluated for a 6-week history of intermittent dyspnea, with a recent episode over the past 24 hours. The patient was also hyporexic and had vomited 3 times during transport to the hospital. Evaluation by the primary veterinarian 4 weeks prior led to a diagnosis of feline asthma based on clinical signs and findings on thoracic radiography. The cat was prescribed oral administration of prednisolone, theophylline, and terbutaline as needed.
On the initial physical examination, the cat was tachypneic (110 breaths/min; reference range, 15 to 30 breaths/min) and dyspneic, with wheezes auscultated in all lung fields. A focused assessment with sonography in trauma scan on intake revealed multiple ring-down artifacts bilaterally in the thorax. The cat was placed in an oxygen cage set at 70% oxygen for stabilization; shortly later, thoracic radiographic images were acquired for characterization of the cause for dyspnea (Figure 1).
Ventrodorsal (A) and right (B) and left (C) lateral thoracic radiographic images of a 12-year-old 4.0-kg castrated male domestic shorthair cat evaluated for intermittent periods of dyspnea over the past 6 weeks and with a recent episode over the past 24 hours.
Citation: Journal of the American Veterinary Medical Association 260, 12; 10.2460/javma.22.02.0082
Diagnostic Imaging Findings and Interpretation
Thoracic radiography revealed a severe alveolar pattern within the right cranial and middle lung lobes with associated severe mediastinal shift to the right as evidenced by the displacement of the cardiac silhouette on the ventrodorsal projection (Figure 2); these changes were consistent with complete collapse of these 2 lung lobes. Rounded circular gas lucencies were superimposed with the cardiac silhouette in the region of the aforementioned lung lobes. In the right caudal lung lobe, there was a moderate to severe alveolar pattern with a vesicular component. Primary differential diagnoses included neoplasia with bronchial obstruction and secondary lung lobes collapse followed by pneumonia, specifically necrotizing pneumonia (given the vesicular component), and chronic effusion with adhesions (eg, pyothorax).
Same images as in Figure 1. There are circular gas opacities (arrows) in the right cranial and right middle lung lobes, superimposed on the cardiac silhouette due to a rightward mediastinal shift. In the right caudal lung lobe (dashed oval), there is a moderate to severe alveolar pattern with a vesicular component.
Citation: Journal of the American Veterinary Medical Association 260, 12; 10.2460/javma.22.02.0082
To further characterize the disease process, the cat underwent general anesthesia and thoracic CT. This revealed an ill-defined soft tissue–attenuating and moderately contrast-enhancing mass starting immediately cranial to the level of the tracheal bifurcation along the right tracheal wall and extending caudally into the right mainstem bronchus (Figure 3). Based on location, the mass originated from the bronchus or the trachea and protruded into the tracheal lumen, occluding up to half of the tracheal lumen and right mainstem bronchus. The mass extended laterally into the bronchi of the right cranial and middle lung lobes, causing obstruction and secondary collapse of these lobes. The more distal portions of the right cranial and middle bronchi contained fluid-like material and residual gas; similar fluid material was present in the accessory bronchus and intermittently in the right caudal bronchus. The right cranial, middle, and accessory lung lobes contained small amounts of gas but overall were mostly collapsed. The right caudal lung lobe had mildly rounded margins, gas stippling along the midventral aspect resembling a vesicular pattern, and ground-glass opacity with moderate thickening of the wall of the bronchi in the dorsal aspect. The left lung had a slight ground-glass opacity along the ventral aspect of the cranial lobe, consistent with atelectasis, but was otherwise unremarkable.
Postcontrast transverse (A; at the level of the caudal end plate of T5), precontrast high-resolution transverse (B; at the level of the midbody of T5), and postcontrast multiplanar reconstructed dorsal oblique (C; at the level of the tracheal bifurcation) plane CT images of the thorax and dorsal 3-D CT volume rendering of the trachea (D) of the cat described in Figure 1. At a level cranial to the tracheal bifurcation, there is a soft tissue–attenuating mass (white arrows) centered on the right side of the trachea (T), occluding approximately half of the tracheal lumen (arrowhead; D) and resulting in a right-sided bronchial obstruction. Immediately cranial in the collapsed right cranial lung lobe, there is a circular gas-attenuating structure (black arrow; B) that corresponds with one of the circular gas opacities indicated in Figure 2, consistent with a gas-filled bronchus. Images A, B, and C are displayed in a soft tissue window (window width, 400 HU; window level, 40 HU) with slice thicknesses of 1.25, 0.625, and 0.28 mm, respectively.
Citation: Journal of the American Veterinary Medical Association 260, 12; 10.2460/javma.22.02.0082
Treatment and Outcome
The location of the mass and extent of injury to the right lung lobes indicated this lesion was inoperable. Given the clinical signs and poor prognosis, the owners elected euthanasia and consented to necropsy.
Necropsy findings were consistent with the features evident on radiography and CT. There was a mass that originated from the tracheal mucosa and extended into the lumen immediately cranial to the tracheal bifurcation, which nearly completely obstructed airflow to the right lung lobes. Results of histopathology indicated tracheal adenocarcinoma. In the right lung lobes, there was evidence of severe segmental subacute necrosuppurative bronchopneumonia, bacterial colonies, and intravascular thrombi. Left lung lobe findings included mild multifocal segmental edema and alveolar histiocytosis.
Comments
The cat of the present report had tracheal adenocarcinoma. Primary tracheal neoplasia is uncommon in cats. The most common feline tracheal tumors include lymphoma and carcinomas, usually occurring in older patients. Upper respiratory signs are the most common clinical presentation for tracheal masses, including dyspnea and stridor, but some affected animals may have coughing or wheezing.1,2
Due to the naturally high contrast with air in the trachea, a discrete mass is often seen on radiography.1,2 Another common radiographic finding for tracheal tumors is tracheal narrowing or compression, which was noted in all cats of a recent case series.3 A discrete tracheal mass was not seen on radiographic examination of the cat of the present report. This was likely due to the lateralized position of the mass along the right tracheal wall, which would have been projected ‘face-on’ on lateral views of the thorax, hence preventing the formation of a distinct edge outlined by luminal gas, as would have been seen if this mass was along the ventral or dorsal wall of the trachea and caught tangentially by the X-ray beam. On the ventrodorsal view, the trachea was obscured by the midline sternal and spinal osseous structures, preventing a good assessment of the tracheal lumen. The soft tissue opacity of the collapsed or partially consolidated right lung lobes also likely obscured the tracheal mass lesion.
Given the loss of volume in the right cranial and middle lung lobes, the primary consideration was bronchial obstruction, such as due to infiltrative neoplasia close to the pulmonary hilus, or bronchial obstruction due to mucus and infectious bronchial secretions. Changes in the right caudal lung lobe were consistent with concurrent pneumonia, specifically necrotizing pneumonia (given the vesicular component). Less likely consideration was given to chronic infectious pleural disease with effusion and adhesions such as pyothorax. To better characterize these lesions, CT was performed and provided identification of a mass cranial to the tracheal bifurcation, either tracheal or bronchial in origin, that was partially obstructing the trachea and bronchi. The mass resulted in bronchial obstruction that caused collapse of the right cranial and right middle lung lobes. The right accessory lung lobe was also collapsed due to a large amount of non–contrast-enhancing fluid obstructing the lumen. The changes in the right caudal lung lobe were likely secondary and attributed to concurrent bronchopneumonia. CT imaging was beneficial in this case, but endoscopy, which allows for biopsy, is the current recommendation for definitive diagnosis of tracheal masses.4
The current primary treatment recommendation for tracheal masses is resection and anastomosis of the trachea if possible, but there are many lower respiratory complications associated with this option. Survival time for patients that underwent this procedure has ranged from 25 days to 32 months, depending on the tumor type.4 Other treatment options include debulking the mass through bronchoscopy, combinations of chemotherapy and radiation, intraluminal stenting, and tracheostomy as a last option.1–3 Multimodal treatments without surgical intervention have shown promising results, with a survival time of 755 days for 1 patient.5
Overall, the patient had common clinical signs consistent with a tracheobronchial obstruction. Although a distinct tracheal mass lesion may not be seen radiographically, it should be a consideration when lung lobe collapse with no obvious mass effect or other cause, such as pleural effusion or pneumothorax, is seen. For the cat of the present report, advanced cross-sectional imaging with CT was needed to narrow the list of differential diagnoses on the basis of radiographic findings and ultimately allowed identification of the tracheal mass as the cause for the clinical signs and lung lobes collapse with associated mediastinal shift visible radiographically.
Acknowledgments
No external funding was used in the management or reporting of this case. The authors declare that there were no conflicts of interest.
References
- 1. ↑
Jakubiak MJ, Siedlecki CT, Zenger E, et al. Laryngeal, laryngotracheal, and tracheal masses in cats: 27 cases (1998–2003). J Am Anim Hosp Assoc. 2005;41(5):310–316.
- 2. ↑
Carlisle CH, Biery DN, Thrall DE. Tracheal and laryngeal tumors in the dog and cat: literature review and 13 additional patients. Vet Radiol Ultrasound. 1991;32(5):229–235.
- 3. ↑
Howard J, Fisher J, Tolbert MK. Invasive tracheal neoplasia in eight cats: descriptive cases and review of the current literature. JFMS Open Rep. 2017;3(1):2055116917690074. doi:10.1177/2055116917690074
- 4. ↑
Jamjoom L, Obusez EC, Kirsch J, Gildea T, Mohammed T-L. Computed tomography correlation of airway disease with bronchoscopy—part ll: tracheal neoplasms. Curr Probl Diagn Radiol. 2014;43(5):278–284.
- 5. ↑
Azevedo C, Brawner W, Lindley SS, Smith A. Multimodal non-surgical treatment of a feline tracheal adenocarcinoma. JFMS Open Rep. 2017;3(1):2055116916689630. doi: 10.1177/2055116916689630
