Introduction

This case report describes a cat with pulmonary carcinoma that caused bronchial obstruction and subsequent pneumonia. This case demonstrates that a bronchial stent and radiation therapy may be a reasonable palliative treatment for malignant bronchial obstruction.

Case Report

A 10 yr old, 3.7 kg, female spayed, feral, domestic shorthair was referred for treatment of a large multilobular, cystic accessory lung lobe mass causing consolidation of the right caudal lung lobe due to bronchial obstruction confirmed on a computed tomography (CT) scan. Episodes of dyspnea, decreased appetite, hiding behavior over the past few days, and intermittent coughing/choking episodes over several months were reported. Physical examination was unremarkable. Complete blood count and serum chemistry profile revealed a mild neutrophilia (20.76 × 10³/μL [2.62–15.17 × 10³/μL], monocytosis (1.17 × 10³/μL [0.04–0.53 × 10³/μL], and hypoalbuminemia (1.9 g/dL [2.6–3.9 g/dL]).

Consultation with the owner included surgical, medical, and interventional treatment options with follow-up radiation if indicated. Because of the invasiveness of the mass, complete surgical margins were unlikely. The owner also had strong reservations about postthoracotomy management of the feral animal in the intensive care unit and at home. Tracheobronchoscopy and stenting of the obstructed bronchus was ultimately pursued in order to biopsy the tumor, establish bronchial patency and permit drainage of the involved lung lobe, acquire culture and sensitivity samples, and provide improved ventilatory capacity.

Terbutaline sulfate^a (0.01 mg/kg IV), midazolam hydrochloride^b (0.2 mg/kg IV), and butorphanol tartrate^c (0.2 mg/kg IV) were administered as premedication, followed by alfaxalone^d (1mg/kg IV) for anesthetic induction. A radio-opaque 4.5 mm endotracheal tube was placed, and anesthesia was maintained with butorphanol tartrate (0.6 mg/kg/hr), midazolam hydrochloride (0.36 mg/kg/hr), and alfaxalone (5 mg/kg/hr). The tracheobronchoscopy was performed through the endotracheal tube using an 8 French flexible digital ureteroscope^e in combination with fluoroscopy.^f A multilobulated mineralized mass surrounded by a moderate amount of purulent material was identified at the bronchi leading to the right middle, caudal, and accessory lung lobes. A stone basket^g was used to obtain tissue samples. A 0.035 inch angled hydrophilic guidewire^h was passed through the ureteroscope using fluoroscopic guidance and was advanced beyond the mass into the right caudal bronchus (RB3). The scope was removed and a 5 French marker catheterⁱ was advanced across the obstruction. The wire was removed and ∼1–2 mL of a 50:50 iohexol^j and saline mixture was injected through the marker catheter under fluoroscopic guidance to outline and measure the borders of the mass as well as to calculate the bronchial dimensions for stent placement. An 8 × 40 mm laser-cut self-expanding metal stent^k was deployed, expanding the bronchus, extending 5 mm proximal and distal to the obstruction, restoring patency, and providing drainage (Figure 1A). Bronchoscopy and fluoroscopy were used to confirm bronchial patency and appropriate positioning. Purulent material contained within the infected airway was aspirated using a sterile suction catheter and a suction trap, and a culture was obtained. The total procedure time was 60 min.

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Immediate postoperative thoracic radiography confirmed persistent right caudal lung consolidation with right cranial and middle lobe hyperinflation, and the mass partially replacing and expanding the accessory lung lobe (Figure 2A). Enrofloxacin^l (5 mg/kg IV) and ampicillin/sulbactam^m (30 mg/kg IV), cefovecinⁿ (8 mg/kg subcutaneous [SQ]), cyproheptadine^o (0.4 mg/kg transdermal [TD]), and ondansetron^p (1 mg/kg TD) were administered postoperatively. The cat recovered from anesthesia uneventfully with 40% oxygen supplementation for 4 hr and was discharged that evening. Cyproheptadine transdermal cream (0.3 mg/kg TD q 12 hr) and ondansetron transdermal cream (1 mg/kg TD q 12 hr) were sent home for continued administration.

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The owner reported immediate resolution of the cough as well as improved breathing and appetite following hospital discharge. The culture results identified Pasteurella multocida sensitive to cefovecin. The biopsy report confirmed a moderately differentiated carcinoma (presumptive grade II) with a mitotic count 8 per 10 high-power field. A CT scan^q was repeated 2 wk after the operation, which revealed a persistent accessory lung lobe mass and partial resolution of the pneumonia accompanied by partial atelectasis but improved aeration of the right caudal lung lobe (Figure 2B). The resolution of the infection unmasked a pulmonary soft-tissue nodule that was concerning for metastatic disease.

At 2.5 wk after the operation, the cat received 4 Gy × 10 doses (total 40 Gy) of daily intensity modulated radiation therapy given over a 12 day course, during which she was hospitalized and premedicated for anesthesia via an IV line to minimize all necessary handling. The 6 mV photon radiation was administered via a linear accelerator^r equipped with a multileaf collimator^s and on-board 2D KVP imaging.^t The patient also received cefovecin (8 mg/kg SQ) and methylprednisolone acetate^u (3.5 mg/kg intramuscular [IM]) on her final radiation treatment day. Thoracic radiographs performed revealed further improved inflation of the right caudal lung lobe (Figure 2C). Methylprednisolone acetate (3.5 mg/kg IM) was administered every 2–3 wk as needed, which improved clinical signs of cough, intermittent dyspnea, and decreased appetite.

At 31 wk after stent placement, the cat became dyspneic. Examination revealed a resting respiratory rate of 48 breaths per minute with marked increased expiratory effort and obstructive breathing pattern. Her weight was 4.29 kg with a body condition score 7/9. Midazolam (0.2 mg/kg IM) and alfaxalone (1 mg/kg IM) were administered, and thoracic radiography was performed, which was unchanged from previous reports. Blood work was unremarkable. On day two of hospitalization, butorphanol tartrate (0.3 mg/kg IM) and propofol^v (2–3 mg/kg IV titrated to effect) were administered, and a CT scan was performed. The scan revealed a persistent but stable cavitated accessory lung lobe mass with progressive metastatic disease within the lungs and static positioning and patency of the stent. An ∼1.1 cm new intraluminal nodule was also noted in the tracheal lumen at the level of the tracheal bifurcation, obstructing the lumen of the right caudal mainstem bronchus. A cavitated hepatic mass possibly consistent with metastatic disease was also identified. Tracheobronchoscopy confirmed the new intraluminal mainstem bronchial mass a few centimeters cranial to the stent margin, causing almost 100% obstruction. Loop cautery was used to debulk 90% of the mass. The histopathology of this new mass also confirmed a respiratory epithelial carcinoma with a mitotic count of 12 per 10 high-power field. At 34 wk, the cat had increased cough episodes again. A decision was made to repeat tracheobronchoscopy, which revealed growth of the tumor migrating out and almost completely obstructing the right bronchus. An 8 × 60 mm laser-cut self-expanding metal stent was placed using a 0.035 inch angled hydrophilic guidewire through the previous stent (Figure 1B). An endotracheal lavage was performed and submitted for culture and susceptibility. The procedure was performed in 26 min. Before recovery, the patient received cefovecin (8 mg/kg SQ) and methylprednisolone acetate (3.5 mg/kg IM). The tracheal culture revealed Pasteurella sp., with predictable susceptibility to cefovecin, and normal flora.

At 46 wk, the cat was 3.12 kg with a 3/9 body condition score. Thoracic radiography revealed a new finding of a right caudal alveolar pulmonary pattern (Figure 2D). There were also progressive pulmonary soft-tissue nodules, consistent with progressive metastatic disease, and an unchanged hepatic mass with a loss of serosal detail, suggesting peritoneal effusion or focal peritonitis.

At 47 wk after the initial stent placement, the cat was evaluated for repeat tracheobronchoscopy and debulking of the pulmonary neoplasia due to a progressive cough and clinical decline at home. The cat was sedated with butorphanol tartrate (0.3 mg/kg IV), midazolam (0.2 mg/kg IV), and alfaxalone (4 mg/kg IV). The tracheobronchoscopy revealed progressive neoplastic disease with major ingrowth into the previously placed stent. Debulking was performed; however, additional procedures were deemed minimally beneficial because of the progression and extent of the disease. The cat was euthanized the next day at home after discharge from the hospital because of a poor quality of life. A necropsy was not performed.

Discussion

In the feline species, bronchial adenocarcinomas are the most common primary pulmonary tumors.^1–5 In cats, these tumors have significant intrapulmonary metastatic potential, with a 35–65% chance of having pulmonary infiltrates or pleural effusion at the time of diagnosis. Additionally, these tumors have distant metastatic potential to sites such as skin, eyes, skeletal muscles, bones (particularly distal phalanges), and abdominal organs.^1,5,6 Similar to humans, surgical removal is the preferred treatment for primary solitary pulmonary tumors in cats.^7,8 Because cats usually mask evidence of respiratory disease until the neoplasm is well advanced, surgical success is often limited, rendering a poor prognosis in the majority of cases.^1,2,5,8 Between 50 and 75% of feline patients demonstrate extensive pulmonary disease or presence of metastatic disease at time of diagnosis and are therefore not considered good candidates for surgical resection.⁷ In one published study, cats with pulmonary carcinoma had a reported overall mean survival time of 115 days after surgical intervention, and all of the cats died of metastatic disease.⁷ A more recent study showed that, in addition to histologic grade, the presence of clinical signs, pleural effusion, evidence of metastasis, and any stage beyond a single tumor with no nodal or pleural/distal metastases are each negative prognostic indicators.⁸ Moderately differentiated tumors had a mean survival time of 698 days (12 cats, range 19–1526 days), whereas poorly differentiated tumors had a median survival time of 75 days (9 cats, range 13–634 days).⁷ Most cats die of metastatic disease. Without treatment, the survival is typically reported as poor.^1–5

In this current case report, the tumor was a moderately differentiated adenocarcinoma, which therefore should hold a better prognosis. However, it was complicated with extensive disease advancing up the mainstem bronchus towards the hilus, causing bronchial obstruction and infection of the adjacent lung lobe. Additionally, there was suspect intrapulmonary metastatic disease identified after drainage of the infected lung lobe. The patient was also feral, and therefore the owner had declined a thoracotomy. As such, this was a high-risk patient facing significant treatment limitations. Although radiation therapy was explored as the initial treatment consideration, the concern for the lung obstruction and the high suspicion of a secondary lobe infection made this option unfavorable because of the potential risks. A bronchial stent was chosen to help manage the airway obstruction and help relieve the infection through culture and drainage before radiation.

Bronchial stents have been used regularly in humans for a variety of conditions associated with airway attenuation.⁹ One study concluded advantages for the use of bronchial stents over other treatment options for localized external compression or malacia of the tracheobronchial tree, which reported excellent tolerance and improved airflow for substantial postoperative time periods (average 10 mo).¹⁰ A retrospective study showed that treatment of malignant airway obstruction due to advanced lung cancer with a combination of initial stenting followed by radiation led to a better survival in comparison to either stenting or radiation alone.¹¹ Complications such as migration and fatal hemoptysis can occur following bronchial stent placement and have been reported uncommonly in the human literature.¹¹ There is very little information reported on bronchial stenting and bronchoscopic debulking in the veterinary literature. One case report described bronchial stent placement in a dog who had developed acute pulmonary edema of an unknown cause. This dog ultimately succumbed to congestive heart failure after 102 days.¹² There is only one published paper describing the placement of bronchial stents in cats. That case report described a cat with a heart-based mass that induced bilateral mainstem bronchial obstruction. Stent placements successfully improved the patient’s dyspnea.¹³ Complications in that cat included severe hypoxia during stent deployment, transient self-limiting pneumothorax, bronchopneumonia, and transient worsening of cough immediately after the operation. The cat was euthanized 44 wk following stent placement because of regurgitation, which was thought to be related to tumor invasion into the esophagus. In our current case report, the initial stent placement was very successful. There was no hypoxia during the placing of the bronchial stent in the patient, likely because the endotracheal tube did not need to be removed for unilateral stent placement because this patient was only suffering from unilateral obstruction. There was also no transient worsening in cough immediately following stent placement, as noted in the previous case report. No stent migration was noted, because the stent size was chosen based on the marker catheter calibration and measurements. Additionally, 8–10 mm diameter tracheal stents are commonly used in cats.

A study looking at radiation’s effect on normal tissue in dogs affirms that radiation has been shown to alter pulmonary epithelial permeability, and that dose-dependent changes in pulmonary physiology may precede obvious structural changes.¹⁴ Pneumonitis can result in the early phase and, depending on severity, can significantly increase the risk of future pulmonary fibrosis, which is the most common radiation-induced complication following treatment of thoracic neoplasms reported in human literature.¹⁵ The safety of radiation therapy performed on an infected lung is a consideration that raises concern for causing more harm than benefit by further exacerbating the overall tissue damage and also by impeding the immune response and the tissue’s ability to heal.^16,17 Radiation can worsen a preexisting infectious process, which could promote necrosis and breakdown of tissue, which can lead to further complications such as pyothorax pleuritis, and/or sepsis. As such, radiation was contraindicated in this patient without first addressing the obstruction and infection. Suspect pneumonitis secondary to radiation therapy was observed at 37.5 wk after stent placement (35 wk after radiation therapy). However, histopathology would be required to differentiate pneumonitis from progressive metastasis. There is scant published information regarding the use of chemotherapy for feline pulmonary carcinomas. One study evaluating response rate following Mitoxantrone chemotherapy alone for a variety of feline carcinoma types reported only 14% partial remission and 4% complete remission, with many toxic adverse events.¹⁸ No response was noted in the only cat in the group with pulmonary carcinoma.

In this case study, the stent helped re-establish bronchial patency and drain the infected lung. Stent placement improved functional lung capacity and the radiation oncologist’s ability to better identify the tumor margins for radiation treatment planning. The cat maintained a good quality of life following treatment. The cat also remained eupneic with an occasional cough for 236 days. However, because of tumor progression cranial to the initial stent, the lumen had to be debulked a second time before later reinforcement with a second stent. The cat survived an additional 3 mo after the second stent placement before further progression and tumor ingrowth in the second stent. A survival of 323 days (10.7 mo) after initial stent placement was achieved.

Conclusion

Surgical resection is the recommended gold standard curative intent treatment for the management of primary lung tumors in cats. Bronchial stenting of an obstructive bronchus was an effective palliative treatment in this cat because it helped the infection resolve quickly, leading to a resolution of clinical signs. This allowed for safe followup radiation treatment administration to the tumor site to slow down tumor progression. This case demonstrates that bronchial stenting can be considered as a palliative treatment for maintaining bronchial patency in cats with malignant bronchial obstructive disease.