History
A 10-month-old sexually intact male Shetland Sheepdog was evaluated by its primary veterinarian for a 1-day history of decreased appetite and mild lethargy. On physical examination, the dog was noted to have increased respiratory rate and effort with decreased lung sounds on the left side. The dog was not receiving heartworm preventative. The veterinarian performed survey radiography, made a diagnosis of pneumothorax, and performed bilateral thoracocentesis. The dog was referred to a surgical center for advanced imaging and continued care.
On evaluation at the referral center the following day, the owner stated that the dog seemed clinically improved, with a normal appetite and energy level. On physical examination, the dog was bright, alert, and responsive, with no abnormal findings. Additional thoracic radiographs were obtained (Figure 1).
Right lateral (A) and ventrodorsal (B) radiographic views of the thorax of a 10-month-old sexually intact male Shetland Sheepdog that were obtained after bilateral thoracocentesis was performed to treat pneumothorax.
Citation: Journal of the American Veterinary Medical Association 247, 4; 10.2460/javma.247.4.349
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
Moderate retraction of the caudal lung lobe margins from the thoracic wall and diaphragm, decreased pulmonary aeration resulting in increased pulmonary opacity, and cardiosternal separation are radiographically evident. These findings are consistent with pneumothorax. The diaphragm appears caudally displaced and flattened. A bullous-appearing gas opacity with a thin, outer soft-tissue opaque rim, possibly representing pleural thickening or scant pleural effusion, is evident within the caudal aspect of the thoracic cavity on the right side. Internal, soft-tissue opaque septae are observed within this bullous structure (Figure 2). On the lateral view, poorly defined bullae are suspected along the caudal margin of the collapsed left caudal lung lobe. A minimal amount of gas is visible along the thoracic wall on the right side, most likely iatrogenically introduced at the time of prior thoracocentesis. The cardiac silhouette and pulmonary vasculature appear normal, and no other abnormalities are seen.
Same right lateral (A) and ventrodorsal (B) radiographic images as in Figure 1, with areas of interest enlarged (C and D). On the lateral views, note the rim-like curvilinear soft tissue opacities associated with a bullous-appearing structure in the right caudal aspect of the thorax (arrows). On the ventrodorsal views, the left caudal lung lobe appears collapsed (arrows). There is retraction of caudal lung lobe margins from the thoracic wall and dorsal deviation of the cardiac silhouette from the sternum secondary to pneumothorax.
Citation: Journal of the American Veterinary Medical Association 247, 4; 10.2460/javma.247.4.349
Thoracic CT was performed, and multiple large, bullous, gas-filled structures were identified within the thorax. Web-like striations were identified within the gas pockets, and a bubble-like appearance to the gas was noted within the right cranial and right and left caudal portions of the thorax. The bubble-like appearance was considered to be attributable to pleural blebs or pulmonary bullae. The probable large pulmonary bullae could be congenital, secondary to trauma, or secondary to pleuritis. A minimal amount of free pleural air was visible. There was no evidence of pleural effusion. The remaining intrathoracic structures were unremarkable. A dorsal reformation of the CT images was constructeda to facilitate observation of the extent of the bullae (Figure 3).
Dorsal reformatted CT image of the thorax made dorsal to the heart base. Note the bullous structures in the right cranial, right caudal, and left caudal lung lobes. Minimal pleural gas (pneumothorax) is visible in the caudal aspect of the thorax peripheral to the bullae. This is best seen on the right along with retraction of the lungs from the thoracic wall. The stairstep artifact on this image is likely due to reformatting of the 3-mm transverse slices. Although better image quality during reformatting could have been obtained with thinner original slices, this image is nonetheless of diagnostic quality.
Citation: Journal of the American Veterinary Medical Association 247, 4; 10.2460/javma.247.4.349
Treatment and Outcome
After multiple additional episodes of pneumothorax and subsequent thoracocentesis within the week, surgery was determined to be the only viable option and multiple partial lobectomies were performed via median sternotomy. Approximately 90% of the right cranial lung lobe was removed, along with partial lobectomies of the left cranial, right caudal, left caudal, and right middle lobes. All 5 pulmonary tissue samples were sent for histologic evaluation, which resulted in a histopathologic diagnosis of intermixed marked pulmonary atelectasis and emphysema with pulmonary hemorrhage. Given the signalment and history of the patient, cause of the bullae was most consistent with a congenital origin.
The dog underwent suture removal 2 weeks after surgery and was reported to be doing well. Additional recheck evaluations up to 5 months after the original surgery continued to indicate that the patient was clinically normal.
Comments
Radiographs are excellent for diagnosis of pneumothorax; however, they may be poor for identifying pulmonary bullae or pleural blebs.1 In the case described in the present report, the severity and extent of the pulmonary bullae were not appreciated radiographically. Computed tomography is considered a better modality for identification of the underlying cause of pneumothorax, compared with radiography, and allows identification of the individual lung lobes affected with pulmonary bullae in most instances.1 Computed tomography is not a perfect diagnostic tool because bullae size and rupture may affect visibility and diagnosis, possibly leading to clinical inaccuracies.2 In the dog of the present report, CT proved to be more specific than radiography for detecting pulmonary bullae and greatly assisted with the surgical approach and planning; however, CT did not identify the true extent of the bullae, which was discovered during surgery.
If bullae are identified on thoracic radiographs, treatment is generally not advised unless the patient becomes clinically affected, such as with development of pneumothorax.3 Bullae in the dog of the present report were accompanied by severe clinical signs, and multiple treatment modalities were considered, including pulmonary lobectomy and indwelling continuous suction thoracostomy tube. Because of the large amount of lung tissue expected to be removed, surgery was considered a salvage procedure in this instance. Only 50% of functional lung tissue may be removed with the expectation of returning to normal daily activities, and removal of > 75% of functional pulmonary tissue at 1 time results in death.4
Congenital bullae and subsequent spontaneous pneumothorax have been described, and cranial lung lobes have been noted to be the most commonly affected.5 Most dogs with pulmonary bullae have more than 1 lesion, and more than half have bilateral lesions; most have excellent outcomes after surgery to remove the affected tissue.5
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1. 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.
2. 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.
3. Nelson OL, Sellon JK. Pulmonary parenchymal disease. In: Ettinger SJ, Feldman EC, eds. Textbook of veterinary internal medicine. St Louis: Elsevier/Saunders, 2005; 1258–1259.
4. Monnet E. Lungs. In: Tobias KM, Johnston SA, eds. Veterinary surgery: small animal. Vol 2. St Louis: Elsevier/Saunders, 2012; 1758–1767.
5. 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.
