History
An 8.7-year-old 3.9-kg (8.6-lb) spayed female Shih Tzu was evaluated for dyspnea and episodes of coughing that started after being retrieved from a dog daycare facility earlier in the day. The owners reported that a larger dog had collided with their Shih Tzu and that no other trauma or violent interactions had been observed. The owners also reported that their dog was not receiving any medications, was current on vaccinations, and had not had any previous abnormal clinical signs, except during an instance of pancreatitis 5 years earlier.
On physical examination, the dog was quiet and alert and had a respiratory rate of 78 breaths/min (reference range, 10 to 30 breaths/min), heart rate of 144 beats/min (reference range, 80 to 130 beats/min), and rectal temperature of 39.1°C (102.4°F; reference range, 38.0°C to 39.1°C [100.4°F to 102.4°F]). Lung sounds were muffled bilaterally, and the dog had an increased respiratory effort with an abdominal component to respiration. The remainder of the findings on physical examination were unremarkable.
Abnormal results of hematologic assessmentsa included a slightly high Hct (56%; reference range, 37% to 55%) and hyperglycemia (126 mg/dL; reference range, 60 to 115 mg/dL); however, the remaining findings were within reference limits, including plasma concentration of total solids (5.7 g/dL; reference range, 5.5 to 7.5 g/dL). Three-view thoracic radiographic images were obtained (Figure 1).
Right lateral (A), left lateral (B), and ventrodorsal (C) thoracic radiographic images of an 8.7-year-old 3.9-kg (8.6-lb) spayed female Shih Tzu with dyspnea and episodes of coughing that started suddenly a few hours after colliding with a larger dog.
Citation: Journal of the American Veterinary Medical Association 258, 10; 10.2460/javma.258.10.1071
Right lateral (A), left lateral (B), and ventrodorsal (C) thoracic radiographic images of an 8.7-year-old 3.9-kg (8.6-lb) spayed female Shih Tzu with dyspnea and episodes of coughing that started suddenly a few hours after colliding with a larger dog.
Citation: Journal of the American Veterinary Medical Association 258, 10; 10.2460/javma.258.10.1071
Right lateral (A), left lateral (B), and ventrodorsal (C) thoracic radiographic images of an 8.7-year-old 3.9-kg (8.6-lb) spayed female Shih Tzu with dyspnea and episodes of coughing that started suddenly a few hours after colliding with a larger dog.
Citation: Journal of the American Veterinary Medical Association 258, 10; 10.2460/javma.258.10.1071
Radiographic Findings and Interpretation
Thoracic radiography revealed a large volume of free gas in the right hemithorax and less in the left hemithorax (Figure 2). The right lung lobes were severely rounded and retracted and had abnormally high soft tissue opacity. The cardiac silhouette was shifted dorsally and toward the left, the mediastinum was shifted leftward, and there was a tented appearance of the diaphragm. On the basis of findings from physical and radiographic examinations, tension pneumothorax was diagnosed.
Same images as in Figure 1. There is a moderate amount of gas opacity present in the pleural space (asterisks), more severe in the right versus left hemithorax. The right lung lobes (RCr, RM, and RCd) are severely rounded, retracted (arrows), and atelectatic. The cardiac silhouette is displaced dorsally and toward the left. Tenting of the costal attachments of the diaphragm is evident (arrowhead). There is an ovoid gas opacity structure (approx 7.6 × 3.7 × 3.4 cm) with a thin, soft tissue opaque rim (dotted outline) in the caudodorsal aspect of the right hemithorax. RCd = Right caudal lung lobe. RCr = Right cranial lung lobe. RM = Right middle lung lobe.
Citation: Journal of the American Veterinary Medical Association 258, 10; 10.2460/javma.258.10.1071
Same images as in Figure 1. There is a moderate amount of gas opacity present in the pleural space (asterisks), more severe in the right versus left hemithorax. The right lung lobes (RCr, RM, and RCd) are severely rounded, retracted (arrows), and atelectatic. The cardiac silhouette is displaced dorsally and toward the left. Tenting of the costal attachments of the diaphragm is evident (arrowhead). There is an ovoid gas opacity structure (approx 7.6 × 3.7 × 3.4 cm) with a thin, soft tissue opaque rim (dotted outline) in the caudodorsal aspect of the right hemithorax. RCd = Right caudal lung lobe. RCr = Right cranial lung lobe. RM = Right middle lung lobe.
Citation: Journal of the American Veterinary Medical Association 258, 10; 10.2460/javma.258.10.1071
Same images as in Figure 1. There is a moderate amount of gas opacity present in the pleural space (asterisks), more severe in the right versus left hemithorax. The right lung lobes (RCr, RM, and RCd) are severely rounded, retracted (arrows), and atelectatic. The cardiac silhouette is displaced dorsally and toward the left. Tenting of the costal attachments of the diaphragm is evident (arrowhead). There is an ovoid gas opacity structure (approx 7.6 × 3.7 × 3.4 cm) with a thin, soft tissue opaque rim (dotted outline) in the caudodorsal aspect of the right hemithorax. RCd = Right caudal lung lobe. RCr = Right cranial lung lobe. RM = Right middle lung lobe.
Citation: Journal of the American Veterinary Medical Association 258, 10; 10.2460/javma.258.10.1071
Additionally, an ovoid gas opacity (approx 7.6 × 3.7 × 3.4 cm) with a thin, soft tissue opaque rim was identified in the caudal aspect of the right hemithorax. This finding suggested a large pulmonary bulla or possible gas and soft tissue in the pleural space.
Treatment and Outcome
Thoracocentesis removed 315 mL of air from the right hemithorax, and repeated thoracic radiography revealed substantial improvement (Figure 3). An intravenous catheter was placed in the dog's left cephalic vein, and a constant rate infusion of fentanyl (2 g/kg/h [0.9 g/lb/h], IV) in lactated Ringer solution with 20 mEq/L of potassium chloride at 4.2 mL/kg/h (1.9 mL/lb/h, IV) was initiated. The dog was hospitalized overnight in an oxygen cage set at 40% oxygen. Overnight, thoracocentesis was repeated once after a period of increased respiratory effort, and 60 mL of air was removed from the right hemithorax.
Right lateral thoracic radiographic image of the dog described in Figure 1 after thoracocentesis showing improved pneumothorax but persistence of an ovoid gas opacity with a thin, soft tissue opaque rim (dotted outline) in the caudodorsal aspect of the right hemithorax.
Citation: Journal of the American Veterinary Medical Association 258, 10; 10.2460/javma.258.10.1071
Right lateral thoracic radiographic image of the dog described in Figure 1 after thoracocentesis showing improved pneumothorax but persistence of an ovoid gas opacity with a thin, soft tissue opaque rim (dotted outline) in the caudodorsal aspect of the right hemithorax.
Citation: Journal of the American Veterinary Medical Association 258, 10; 10.2460/javma.258.10.1071
Right lateral thoracic radiographic image of the dog described in Figure 1 after thoracocentesis showing improved pneumothorax but persistence of an ovoid gas opacity with a thin, soft tissue opaque rim (dotted outline) in the caudodorsal aspect of the right hemithorax.
Citation: Journal of the American Veterinary Medical Association 258, 10; 10.2460/javma.258.10.1071
The dog's pneumothorax worsened, and the decision was made for surgical intervention. A median sternotomy and thoracic exploratory surgery were performed. The right caudal lung lobe was diffusely emphysematous and had a large bulla (Figure 4). The other lung lobes appeared grossly normal. A right caudal lung lobectomy and placement of a thoracic tube were performed. The dog recovered uneventfully and was discharged after removal of the thoracic tube 2 days postoperatively. Histologic examination of the resected lung tissue revealed moderate to severe diffuse interstitial fibrosis throughout the tissue sample.
Intraoperative picture of the exteriorized right caudal lung lobe of the dog described in Figure 1 showing the large air-filled bulla that was evident on thoracic radiography. The dog is in dorsal recumbency, and its head is toward the right.
Citation: Journal of the American Veterinary Medical Association 258, 10; 10.2460/javma.258.10.1071
Intraoperative picture of the exteriorized right caudal lung lobe of the dog described in Figure 1 showing the large air-filled bulla that was evident on thoracic radiography. The dog is in dorsal recumbency, and its head is toward the right.
Citation: Journal of the American Veterinary Medical Association 258, 10; 10.2460/javma.258.10.1071
Intraoperative picture of the exteriorized right caudal lung lobe of the dog described in Figure 1 showing the large air-filled bulla that was evident on thoracic radiography. The dog is in dorsal recumbency, and its head is toward the right.
Citation: Journal of the American Veterinary Medical Association 258, 10; 10.2460/javma.258.10.1071
Comments
Acute respiratory distress is a veterinary emergency that requires rapid diagnosis of the underlying cause or causes so that the affected patient can be stabilized properly. Pneumothorax in veterinary patients can occur secondary to trauma or may be spontaneous with underlying lung disease. Spontaneous idiopathic pneumothorax may be caused by pulmonary blebs, bullae, or cystic lesions in the lung parenchyma.
Radiographic findings associated with these conditions often include unilateral or bilateral pneumothorax and occasionally pneumomediastinum. For the dog of the present report, results from the initial radiographic examination led to a diagnosis of tension pneumothorax owing to the extent of abnormal gas opacities present, retraction of the right lung lobes, displacement of the cardiac silhouette and mediastinum, and tenting of the diaphragm. Additionally, this dog had a thin-walled radiolucent structure, consistent with pulmonary cyst or bulla, evident in the caudal aspect of the right hemithorax. Bronchogenic cysts may be considered for gas opacities surrounded by thin radiopaque structures in the thorax.1 These cysts can develop secondary to infection or chronic bronchitis or bronchiectasis.1 However, blebs and bullae (pseudocysts) are often not radiographically identifiable.2 When present, bullae are often described as focal, spherical, discrete lesions > 1 cm in diameter that are sharply demarcated by a thin wall.3 The immense size of the thin-walled radiolucent lesion in the dog of the present report prompted a question of whether a pulmonary cyst or bulla could attain such size and remain intact, given their presumed fragility associated with spontaneous rupture. The presence of collapsed and retracted lung lobes further complicated evaluation for underlying pulmonary disease in the dog of the present report.
In addition to radiography, CT can be used to help identify underlying pulmonary lesions and aid in surgical planning when warranted. Although CT has poor sensitivity (42% to 58%) for identifying bullae and other causes of spontaneous pneumothorax,4 it better identifies affected lung lobes than does radiography.5 Identification of a bulla by either of these imaging modalities may not confirm or localize a source for pneumothorax, and ruptured or leaking bullae often appear as atelectatic lung tissue that may further obscure underlying abnormalities. Computed tomography could have been performed for the dog of the present report to further evaluate the abnormal findings on radiography; however, radiographic evidence of a suspected bulla combined with intractable pneumothorax warranted a complete surgical exploration, and CT was therefore not performed. Radiography is often the first line of diagnostic imaging for patients with pneumothorax, with CT generally used for more detailed identification of lesions. Neither modality can guarantee specific localization of clinically meaningful lesions, and concurrent anomalies may further disguise underlying conditions.
When surgical treatment is warranted, findings on diagnostic imaging may help to guide the surgical approach; however, regardless of approach, a complete exploratory assessment of the thoracic cavity is advised. Thoracic exploration for the dog of the present report confirmed the presence of a large bulla with diffuse emphysematous change throughout the right caudal lung lobe. Lobectomy of the affected right caudal lung lobe resolved the dog's tension pneumothorax and secondary clinical signs. A ruptured smaller bulla in this lung lobe may have resulted in the pneumothorax because no obvious leak was found in the large bulla.
Radiographic signs consistent with emphysematous pulmonary lesions typically include a fully expanded lung with decreased opacity.3 However, the dog of the present report had retracted lung lobes that obscured radiographic evidence of emphysema. The combined presence of a bulla with emphysematous and fibrous changes has been reported in a dog with congenital lobar emphysema and concurrent pneumothorax and pneumomediastinum.6 Similarly, the findings in the dog of the present report suggested that alterations in the pulmonary parenchyma likely predisposed the dog to rupture of the visceral pleura or alveoli with only mild trauma,6 such as colliding with another dog as had occurred before the onset of this dog's clinical signs.
Footnotes
VetScan i-STAT 1 handheld analyzer CHEM8+, Abbott Point of Care Inc, Abbott Park, Ill.
References
- 1. ↑
Dahl K, Rørvik AM, Lanageland M. Bronchogenic cyst in a German Shepherd Dog. J Small Anim Pract 2002;43:456–458.
- 2. ↑
Lipscomb VJ, Hardie RJ, Dubielzig RR. Spontaneous pneumothorax caused by pulmonary blebs and bullae in 12 dogs. J Am Anim Hosp Assoc 2003;39:435–445.
- 3. ↑
Scrivani PV. Nontraditional interpretation of lung patterns. Vet Clin North Am Small Anim Pract 2009;39:719–732.
- 4. ↑
Reetz JA, Caceres AV, Suran JN, et al. Sensitivity, positive predictive value, and interobserver variability of computed tomography in the diagnosis of bullae associated with spontaneous pneumothorax in dogs: 19 cases (2003–2012). J Am Vet Med Assoc 2013;243:244–251.
- 5. ↑
Au JJ, Weisman DL, Stefanacci JD, et al. Use of computed tomography for evaluation of lung-lesions associated with spontaneous pneumothorax in dogs: 12 cases (1999–2002). J Am Vet Med Assoc 2006;228;733–737.
- 6. ↑
Park C, Jang K, Yun S, et al. Congenital lobar emphysema concurrent with pneumothorax and pneumomediastinum in a dog. J Vet Med Sci 2016;78:909–912.
