What Is Your Diagnosis?

Jenn B. Strouse Department of Small Animal Clinical Science, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824.

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Krista M. Gazzola Department of Small Animal Clinical Science, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824.

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Laura L. Nelson Department of Small Animal Clinical Science, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824.

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Nathan C. Nelson Department of Small Animal Clinical Science, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824.

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History

A 2-year-old 5.2-kg (11.4-lb) spayed female domestic shorthair cat was evaluated because of acute dyspnea. One week prior to evaluation, the cat had a right forelimb lameness, the cause of which was unknown. The referring veterinarian performed radiography of the right forelimb; radiographic findings revealed a closed fracture of the distal aspect of the right ulna. The cat was placed under general anesthesia without endotracheal intubation for splint placement. No other injuries or abnormalities were found on physical examination. No signs of respiratory distress were apparent.

At the time of referral, the cat was open-mouth breathing. Orthopnea was evident. Thoracic auscultation revealed stridor, which was appreciated on inhalation and exhalation. Venous blood gas analysis revealed mild hyponatremia (148 mmol/L; reference range, 149 to 156 mmol/L), mild hypochloremia (116 mmol/L; reference range, 117 to 124 mmol/L), and mild metabolic alkalosis (HCO3, 22.6 mmol/L; reference range, 14.7 to 22.1 mmol/L; total CO2, 23.8 mmol/L; reference range, 15.6 to 23.5 mmol/L).

An IV catheter was placed, and propofol (6 mg/kg [2.7 mg/lb], IV, to effect) was administered for anesthetic induction. Endotracheal intubation was routine, with no apparent abnormalities of the upper airway noted during intubation. Thoracic radiography (Figure 1) was performed with the cat under isoflurane-maintained general anesthesia.

Figure 1—
Figure 1—

Left lateral (A) and dorsoventral (B) radiographic views of the thorax of a 2-year-old 5.2-kg (11.4-lb) spayed female domestic shorthair cat with acute dyspnea.

Citation: Journal of the American Veterinary Medical Association 249, 11; 10.2460/javma.249.11.1249

Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →

Diagnostic Imaging Findings and Interpretation

On radiographic evaluation, a 1-cm-long focal, abrupt narrowing of the intrathoracic tracheal lumen is evident at the level of the third intercostal space (Figure 2). There is no gas appreciable in the tracheal lumen at this level. The tracheal wall has a normal radiographic appearance in the segments cranial and caudal to the narrowing. These findings are consistent with tracheal stricture or avulsion. A mild amount of gas is seen ventral to the cardiac silhouette, with slight dorsal elevation of the cardiac silhouette on the left lateral projection, indicating mild pneumothorax. The lungs are well inflated despite the presence of pneumothorax. The trachea caudal to the narrowing is dilated in comparison with the cranial aspect of the trachea. These findings suggest decreased expiratory airflow secondary to tracheal narrowing and are likely influenced by positive-pressure ventilation during anesthesia. Although not visible on radiographic images, an endotracheal tube is present in the cervical portion of the trachea. No subcutaneous emphysema is identified. A mild unstructured interstitial pattern is seen in the ventral portions of the right cranial and middle lung lobes, which is indicative of mild atelectasis or pulmonary contusions.

Figure 2—
Figure 2—

Same radiographic image as in Figure 1. A 1-cm-long focal, abrupt narrowing of the intrathoracic tracheal lumen at the level of the third intercostal space is evident (arrows). No gas is appreciated in the lumen of the trachea at this level. Notice that the cardiac silhouette is elevated; gas opacity is evident between the pericardium and the sternum (arrowhead), indicating mild pneumothorax. Subcutaneous emphysema is not appreciated.

Citation: Journal of the American Veterinary Medical Association 249, 11; 10.2460/javma.249.11.1249

Tracheoscopy revealed an acutely narrowed lumen in the middle portion of the intrathoracic trachea through which a bronchoscopea (outer diameter, 3.8 mm) could not be passed. A 5F red rubber catheter could be passed through the stricture with minimal clearance. Mucopurulent material was appreciated within the tracheal lumen. The trachea cranial to the luminal narrowing was normal in appearance. These findings were consistent with intrathoracic tracheal lumen stricture, likely secondary to traumatic avulsion.

Computed tomography (Figure 3) was used to further evaluate the neck and thorax. Computed tomographic imagesb were obtained before and after IV administration of a contrast agent (iopamidol, 300 mg of iodine/mL; total patient dose, 11 mL). On CT images, the middle portion of the intrathoracic trachea is markedly decreased in diameter. There is moderate circumferential contrast enhancement of the tissue surrounding the tracheal lumen at this level. These findings are interpreted as a focal intrathoracic tracheal avulsion or stricture. A gas-filled esophagus is appreciated dorsal to the tracheal narrowing consistent with aerophagia. A large amount of gas is present within the pleural space bilaterally (greater in volume than was evident on the radiographic images) and is worse on the left side, with decreased lung volume and patchy alveolar and interstitial patterns ventrally (also worse than evident on the radiographic images); these findings are interpreted as pneumothorax with secondary atelectasis.

Figure 3—
Figure 3—

Contrast-enhanced transverse CT image of the thorax at the level of the middle portion of the intrathoracic trachea of the cat in Figure 1 (soft tissue algorithm; window width, 400 Hounsfield units; window level, 50 Hounsfield units; slice thickness, 0.625 mm). Notice the gas-filled esophagus (arrowhead). There is contrast-enhancing soft tissue (arrow), which surrounds a focal decrease in the diameter of the tracheal lumen.

Citation: Journal of the American Veterinary Medical Association 249, 11; 10.2460/javma.249.11.1249

Treatment and Outcome

Terbutaline and dexamethasone were initially administered in an unsuccessful attempt to relieve dyspnea. The cat was maintained in an oxygen cage prior to imaging.

Following imaging, the cat was maintained on general anesthesia, and a routine right fourth intercostal thoracotomy was performed. The avulsed ends of the trachea were identified and debrided of granulation tissue. The ends of the trachea were stabilized with stay suturesc prior to reintubating the caudal portion of the trachea with a sterile endotracheal tube. The tracheal ends were apposed with preplaced sutures of 4-0 polydioxanone that were secured after withdrawal of the endotracheal tube from the incision.d The lungs were submerged in sterile saline (0.09% NaCl) solution, identifying air leakage from the ventral portion of the right cranial lung lobe that was addressed through partial lobectomy.

Ampicillin-sulbactam (30 mg/kg [13.5 mg/lb], IV, q 8 h) and enrofloxacin (4.5 mg/kg [2 mg/lb], IV, q 24 h) were administered in the hospital, and amoxicillin-clavulanate potassium (13.75 mg/kg [6.2 mg/lb], PO, q 8 h) and enrofloxacin (4 mg/kg [1.8 mg/lb], PO, q 24 h) were administered after hospital discharge. Immediate postoperative pain was controlled with fentanyl (3 to 5 μg/kg [1.35 to 2.25 μg/lb], IV, continuously) and buprenorphine (0.1 mg/kg [0.045 mg/lb], IV, q 6 h) in the hospital. Tramadol (2 mg/kg [0.9 mg/lb], PO, q 8 to 12 h) was provided for postoperative analgesia. At recheck examination 2 weeks after surgery, the owner reported the cat was doing well at home with no complications or further dyspnea.

Comments

Differential diagnoses for cats in respiratory distress with stridor include obstructive disease, neoplasia, restrictive lower airway disease, and tracheal trauma. Tracheal trauma includes rupture or avulsion. Tracheal rupture refers to a complete disruption of the tracheal wall, often along the dorsal tracheal membrane, and is often a result of iatrogenic trauma associated with endotracheal intubation.1 Clinical signs of tracheal rupture include acute dyspnea and subcutaneous emphysema, with pneumothorax and pneumoretroperitoneum occurring less frequently.1 In contrast, tracheal avulsion is a rare but well-described injury in cats involving acute hyperextension of the neck, resulting in separation of tracheal rings 1 to 4 cm cranial to the carina.2–4 Although initial acute respiratory distress may be noted, the airway is maintained by intact tracheal adventitia or thickened mediastinal tissue.4 Days to weeks following trauma, a dyspnea-inducing stenosis forms in the tracheal lumen from contraction of granulation tissue at both ends of the avulsion. Thoracic radiography helps to identify tracheal avulsion and rule out other causes of acute dyspnea such as foreign body, asthma, or tracheal rupture.3 Tracheal avulsion can be confirmed with tracheoscopy and CT.

In this case, initial radiographs were interpreted as a stricture or mass effect within the trachea. Endoscopy was pursued to help differentiate the cause of dyspnea and to deliver oxygen past the stricture once confirmed. Computed tomography was pursued because of the difficulty evaluating lower airway disease by use of endoscopy and radiography. As the use of CT in the diagnosis of this condition was straightforward and rapid, eliminated the need to reposition the cat, and provided needed detail on the cause of the dyspnea, its use as a valuable imaging modality when tracheal avulsion is suspected is supported.

Footnotes

a.

Olympus BF-3C160 bronchoscope, Olympus America Inc, Center Valley, Pa.

b.

GE Brightspeed 16 slice CT scanner, GE Healthcare, Waukesha, Wis.

c.

Monocryl, Ethicon Inc, Cincinnati, Ohio.

d.

PDS II, Ethicon Inc, Cincinnati, Ohio.

References

  • 1 Mitchell SL, McCarthy R, Rudloff E, et al. Tracheal rupture associated with intubation in cats: 20 cases (1996–1998). J Am Vet Med Assoc 2000; 216: 15921595.

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  • 2 Griffiths LG, Sullivan M, Lerche P. Intrathoracic tracheal avulsion and pseudodiverticulum following pneumomediastinum in a cat. Vet Rec 1998; 142: 693696.

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  • 3 Schmierer PA, Schwarz A, Bass DA, et al. Novel avulsion pattern of the principal bronchus with involvement of the carina and caudal thoracic trachea in a cat. J Feline Med Surg 2014; 16: 695698.

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  • 4 White RN, Burton CA. Surgical management of intrathoracic tracheal avulsion in cats: long-term results in 9 consecutive cases. Vet Surg 2000; 29: 430435.

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