Spontaneous pneumothorax is an accumulation of air in the pleural space, resulting in closed pneumothorax, without iatrogenic or traumatic causes.1–5 The primary cause of spontaneous pneumothorax in humans1,6,7 and dogs is rupture of subpleural bullae or blebs.1,2,5,8 In the human literature,9 a bleb is defined as an air-filled alveolar dilatation < 1 cm in diameter, located near the pleural surface of the lung. A bulla is defined as an airfilled space > 1 cm in diameter, also located near the pleural surface. In the veterinary literature,4,5,10 a bulla is defined as a large air space in the lung parenchyma, whereas a bleb is a smaller accumulation of air between the visceral pleura and lung parenchyma. In a review of recent retrospective studies,1,2 early surgical intervention was recommended for higher success rates, lower recurrence rates, and shorter hospitalization time, compared with medical management.
Radiography is an excellent means for accurate diagnosis of spontaneous pneumothorax.7,8 However, radiographic diagnosis of bullae, blebs, and their location and number is less successful. In humans, radiographic accuracy for detection of blebs and bullae ranges from 10%3,4 to 60.5%.11 In dogs, accuracy of detection of bullae or blebs on radiographs has ranged from 0%1 to 50%.2 Even in cases in which radiographs allow identification of blebs or bullae, the severity of the lesions may be underestimated.12 Lesions identified radiographically have resulted in an inappropriate surgical approach because of underestimating either the number or location of lesions, especially in the right accessory lobe.13
In humans, CT is a more sensitive method for detection of blebs and bullae than is radiography.12 Accuracy of lesion detection via CT has been reported in the human literature to range from 88%14,15 to 91.8%.16 Blebs and bullae are identified via CT as areas of low attenuation and vascular alteration.9,17–19 Even in cases in which lesions are identified on radiographs, CT is advantageous in identifying more lesions11,12 or better defining lesion size, location,6,9 or surrounding structures.11 Computed tomography has the added advantage of enabling better differentiation of anatomic structures and their relationship to the lesions.11 Therefore, the purpose of the study reported here was to evaluate use of CT of the lungs, compared with conventional radiography, for detection of blebs and bullae associated with spontaneous pneumothorax in dogs. Our hypothesis was that CT would be better than radiography for identification of these causes of spontaneous pneumothorax in dogs.
Criteria for Selection of Cases
The medical records of the Veterinary Referral and Emergency Center and Long Island Veterinary Specialists were searched for dogs in which a diagnosis of spontaneous pneumothorax was made from 1999 to 2002. Records were eligible for inclusion in the study if there was radiographic evidence of pneumothorax and CT of the thorax had been performed. Records were excluded if dogs had a history of trauma associated with development of pneumothorax.
Procedures
Information collected from medical records included age, weight, sex, breed, initial clinical signs, duration of clinical signs, results of laboratory analyses, radiographic and CT findings, surgical approach, surgical findings, lung lobes involved, histopathologic diagnosis, complications, recurrence of pneumothorax, duration of hospitalization, outcome, and followup time. The 7 available radiographs were reviewed by 1 author (JDS). All CT scans were performed with 5-mm slice thickness by use of a third-generation nonhelical scanner.a All CT scans were reviewed by 1 author (JDS). For the radiographic and CT reviews, the author was unaware of the surgical findings and final case outcome. Follow-up information was acquired by review of medical records and contact with referring veterinarians or owners.
Statistical analysis—The level of agreement between radiographic and surgical findings or CT and surgical findings for each lung lobe was assessed by calculating the κ statisticb with a 95% confidence interval. The κ statistic assesses the level of agreement between diagnostic test results beyond what is expected by chance. A κ of 0 indicates that agreement is the same as chance. A κ of 1, the maximum value, indicates perfect agreement. Agreement was defined as identification of a lesion on a lung lobe by use of radiography or CT and confirmation of the lesion by surgical exploration.
Results
Signalment—Records of 12 dogs met the inclusion criteria. Five dogs were admitted to the Long Island Veterinary Specialists and 7 to the Veterinary Referral and Emergency Center. Records of 9 purebred dogs (2 Golden Retrievers and 1 each of Springer Spaniel, Dalmatian, German Shepherd Dog, Husky, Dachshund, American Eskimo, and Gordon Setter) and 3 mixed-breed dogs were evaluated. Median age was 6 years (mean, 6.7 years; range, 3.5 to 12.5 years). There were 3 spayed females and 9 males, of which 6 were neutered and 3 were sexually intact. Median weight was 32.5 kg (71.5 lb; mean, 28.6 kg [62.9 lb]; range, 7.7 to 39.8 kg [16.9 to 87.6 lb]).
Initial complaint—The most common initial complaints were dyspnea (n = 8) or vomiting with dyspnea (3). Median duration of clinical signs prior to examination was available for 11 of the 12 dogs and for dogs with dyspnea alone was 1 day (mean, 65.29 hours [2.7 days]; range, 1 hour to 1.5 weeks); for dogs with vomiting and dyspnea, median duration was also 1 day (mean, 1.83 days; range, 1 to 3.5 days). One dog had dyspnea with decreased appetite.
Laboratory analysis—Results of CBC and serum biochemical analyses were available for all dogs. Results of CBC were within reference ranges in 8 dogs. Three dogs had mature neutrophilia (WBC count, > 17.0 × 103 cells/dL), and 1 dog had mature neutrophilia and hemoconcentration (Hct, > 55%). Seven dogs had serum biochemical values within reference ranges. Three dogs had mild hyperglycemia (serum glucose concentration, > 110 mg/dL). Two dogs had mildly high serum activity of alkaline phosphatase (> 212 U/L). Heartworm tests were performed in 2 dogs, and both results were negative. Baerman fecal examinations were performed in 5 dogs, and all results were negative. A fecal flotation examination was performed in 1 dog and revealed Trichuris vulpis ova.
Radiographic findings—Thoracic radiography was performed in all 12 dogs. Seven sets of radiographs were available for review. Six of the available sets of radiographs had both orthogonal views, either a right or left lateral view, and a ventrodorsal or dorsoventral view. One set contained only the dorsoventral view for review. Five sets of radiographs were unavailable for review; medical records were used for radiographic information for these dogs. Four records contained information regarding both orthogonal views. One record contained only information regarding a lateral radiograph, without reference to left or right side. Eleven dogs had bilateral pneumothorax, and 1 had unilateral, right-sided pneumothorax. Bullae were identified on radiographs of 2 dogs, in the right cranial lung field in 1 dog, and in multiple lung fields in the other dog. No other underlying causes of spontaneous pneumothorax, such as pneumonia, pulmonary abscesses, or neoplasia, were identified.
CT findings—Computed tomography was performed in all 12 dogs. Bullae and blebs were identified as areas of low attenuation, disruption of the vascular pattern by pruning (simplified vascular tree with fewer orders of branching), or distortion of the vessels around the area of decreased attenuation. Lesions were identified in 9 of the 12 dogs. A single bulla was identified in 5 dogs (2 in the right cranial lobe, 1 the right caudal lobe, and 2 in the left cranial lobe [Figure 1]). In 1 dog, multiple blebs were identified in the accessory lung lobe (Figure 2). Three dogs had multiple bilateral bullae and blebs (2 dogs had bullae in left cranial and right caudal lung lobes, and 1 had a bulla on the right cranial lobe and multiple blebs in the left cranial and caudal lobes). In 3 dogs, no bullae or blebs were seen. However, 1 of the 3 dogs had severe pneumothorax and generalized lung lobe atelectasis at the time of CT. This dog also had a history of mild spontaneous pneumothorax 10 months prior that had been resolved by treatment with thoracocentesis alone.
Cross-sectional CT view of a dog at the level of T3. Substantial pneumothorax is visible in the right hemithorax. A = Trachea. B = Heart. C = Pneumothroax. Arrows = Bulla in left cranial lung lobe. Arrowhead = Bronchus.
Citation: Journal of the American Veterinary Medical Association 228, 5; 10.2460/javma.228.5.733
Cross-sectional CT view of a dog at the level of T8. Substantial pneumothorax is evident in both hemithoraces, causing atalectasis of the lung lobes. A = Aorta. B = Esophagus. C = Caudal vena cava. D = Pneumothorax. White arrows = Two blebs in right accessory lung lobe. Black arrow = Bronchus in right caudal lung lobe.
Citation: Journal of the American Veterinary Medical Association 228, 5; 10.2460/javma.228.5.733
Treatment—Ten dogs underwent surgery for definitive treatment for the spontaneous pneumothorax. Two dogs were treated without surgery. In both dogs treated medically, a thoracostomy tube was placed in the left hemithorax and continuous suctionc was maintained. One dog was discharged 7 days after admission with resolution of the pneumothorax. The second dog developed cranial nerve deficits during hospitalization. A CT scan of the thorax and brain was performed. No lung lesions were identified, and the pneumothorax was resolving. However, contrast enhancing lesions were found in the brainstem and pituitary gland. The dog was euthanized because of deteriorating neurologic condition on the tenth day of hospitalization. No necropsy was performed.
Median sternotomy was performed on all dogs that underwent surgical exploration of the thorax. Either partial or complete lobectomy was performed at the surgeon's discretion by use of a surgical stapling device.d In 4 dogs, a single bulla was identified at surgery (2 in the left cranial lobes, 1 in the right cranial lobe, and 1 in the right caudal lobe). Two dogs had multiple bullae (1 in the left cranial and right caudal lobes and 1 in the left cranial, left caudal, and right cranial lobes). Two dogs had multiple blebs identified during sternotomy (1 dog had multiple blebs in the right accessory lobe, and 1 had multiple blebs in the right cranial, right middle, and left cranial lung lobes). One dog had a single necrotic nodule in the right caudal lung lobe. One dog had a hematomalike lesion in the left caudal lung lobe and multiple firm, fibrous lesions in the left cranial and right cranial lung lobes.
Histologic findings—Histologic examination was performed on 9 of the 10 dogs that underwent exploratory thoracotomy. The tenth dog was euthanized during surgery, and histologic examination was not performed. Bullae were confirmed in 4 dogs. Of the remaining 5 dogs, 1 had a segmental region of granulation tissue and airway dilatation that connected with the pleural surface. Another dog had moderate, multifocal, chronic pulmonary hematomas and moderate chronic fibrosing pleuritis. The third dog had focal pulmonary atelectasis and congestion. The forth dog had severe, chronic, fibrosing pleuritis. The final dog had focally extensive necrotizing and suppurative pneumonia, multiple recanalized pulmonary arterial thrombi, and multifocal granulomas.
Complications—Of the 9 dogs that recovered from the exploratory sternotomies, 7 had no postoperative complications. One dog had moderate pleural effusion and hypoalbuminemia (< 2.70 g/dL) that resolved with supportive care. One dog had incisional dehiscence with infection of the sternebrae that required an enbloc resection of the incision 7 days after the initial surgery.
Duration of hospitalization—Ten (9 treated surgically and 1 treated medically) of the 12 dogs were released from the hospital. Two (1 treated surgically and 1 treated medically) dogs were euthanized during hospitalization. Median duration of hospitalization for the 12 dogs was 6.5 days (mean, 6.3 days; range, 1 to 12 days). Of the 10 dogs released from the hospital, median duration of hospitalization was 6.5 days (mean, 6.5 days; range, 3 to 12 days). Of the 10 dogs treated with surgery, median duration of hospitalization was 6 days (mean, 5.9 days; range, 1 to 12 days). Of the 9 dogs treated with surgery and released, median duration of hospitalization was 6 days (mean, 6.4 days; range, 3 to 12 days). The dog treated medically that survived and was released was hospitalized for 7 days.
Outcome—Follow-up for all 10 dogs released from the hospital was available. One dog treated surgically had recurrence of spontaneous pneumothorax 12 days after surgery and was euthanized. No necropsy was performed. Another dog treated surgically developed seizures and ataxia 6 months after surgery and was euthanized. No necropsy was performed. Seven of the dogs presently still alive were treated surgically, and median follow-up time was 10 months (mean, 11.57 months; range, 6 to 18 months). The dog treated medically and released was doing well 14 months after release.
Comparison of radiographic, CT, and surgical findings—Two of the 12 dogs had evidence of bullae on survey radiographs. Both of these dogs underwent CT and exploratory thoracotomy, and the radiographic, CT, and surgical findings were in complete agreement. Ten dogs had no radiographic evidence of bullae, blebs, or any other underlying cause of spontaneous pneumothorax. Seven of the 10 dogs had bullae or blebs identified via CT and underwent an exploratory thoracotomy; in 5 dogs, the CT and surgical findings were in complete agreement. In 1 dog, the CT finding was confirmed during thoracotomy and additional lesions were also found. In another dog, 1 of the 2 CT findings was confirmed at surgery but the other CT finding was not confirmed. In addition, other lesions were found at surgery that were not identified via CT. Three of the dogs had no radiographic or CT lesions. One of the dogs received surgery because of the severity of the pneumothorax and past history of mild pneumothorax. A single 4 × 5-cm bulla on the right caudal lung lobe was identified. Two of these dogs did not receive surgery because of the lack of radiographic and CT findings. One of the dogs was euthanized, and no necropsy was performed. The second dog was clinically normal 14 months later. Radiographic findings did not correlate with surgical findings (κ = 0.306); however, CT findings did correlate with surgical findings (κ = 0.735) on a per lung lobe basis.
Overall, 10 dogs received surgery and 17 affected lung lobes were identified. Four of the 17 affected lobes were identified by use of radiographs. Thirteen of the 17 affected lung lobes were identified by use of CT; however, 1 lobe was incorrectly identified as the right caudal lobe instead of the right cranial lobe.
Discussion
Results of this study suggest that CT is a better modality than radiography for identifying lung lesions that are the underlying cause of spontaneous pneumothorax. In this study, CT was used to identify almost 2.5 times as many lesions as identified via conventional radiography, although results were not as good as reported in the human literature, likely for several reasons. Eleven of the 12 dogs had some degree of pneumothorax, ranging from mild to severe, at the time of the CT scan. With pneumothorax resolved and the lung fully inflated, identification of these lesions is not difficult. As the severity of pneumothorax increases, it becomes more difficult to differentiate the decreased attenuation and alteration in vascular pattern found with bullous lesions versus that found with pneumothorax because of displacement of lung tissue. Also, persistent pneumothorax perpetuates lung lobe collapse, which can make identifying bullous lesions difficult via CT.20–22 In the 11 dogs with pneumothorax at the time of the scan, abnormal tissue could have been wrongly identified as normal, although atalectic, lung tissue. For this reason, we recommend maintaining continuous suction during the CT scan or, if that is not possible, completely evacuating the thorax just prior to the start of the CT scan. The use of continuous suction also allows safe use of positive-pressure ventilation, which further decreases the degree of atalectasis. In retrospect, it may have been informative to subjectively grade the degree of pneumothorax via CT and evaluate the CT and surgical findings in light of the pneumothorax grade. The low number of cases may have also affected the results.
In the present study, median sternotomy was the surgical approach for all dogs that underwent exploratory thoracotomy, as recommended recently.2 In that report, it was suggested that thoracoscopy might be a more viable alternative on the basis of the accuracy of CT scan.2 In our study, CT would have provided accurate information on the appropriate thoracoscopic approach in 8 of the 10 surgical cases. The paraxyphoid-transdiaphragmatic thoracoscopic approach with the dog in dorsal recumbency would have allowed examination of both hemithoraces through a single portal.23 This approach allows complete inspection of both lung fields, including the most dorsal parts when the patient is rolled from side to side.23 Until the accuracy of bulla and bleb identification via CT can be improved, the authors recommend a median sternotomy or a paraxyphoid-transdiaphragmatic thorascopic approach to allow thorough inspection of all lung lobes.
Surgical intervention has been recommended as the treatment of choice for spontaneous pneumothorax.1–5 This recommendation was based on a higher overall success rate than that of medical management, lower recurrence rates, and shorter hospitalization time. The study reported here lacked sufficient numbers of medically treated dogs for comparison. Cost was not evaluated for either treatment. However, only 1 of the 9 surgically treated dogs that were released from the hospital had a recurrence during the followup time, which is consistent with previous surgical recurrence rates of 0% to 25%.1–3,5
It has been reported that use of radiographs can lead to an inappropriate surgical approach for treatment for spontaneous pneumothorax because of underreporting of either the number or location of lesions, especially those involving the right accessory lung lobe as it wraps around into the left hemithorax.13 In the present study, use of radiography failed to identify 13 of the 17 affected lung lobes. Radiographic results might have been better with 3 views of the thorax (right and left lateral views and a ventrodorsal or dorsoventral view), serial radiographs, and radiography after temporary resolution of the penumothorax via thoracocentesis or placement of a tube. Of the lesions identified radiographically, none involved the right accessory lobe. Computed tomography allowed identification of 13 of the 17 lung lobes involved, although the right caudal lung lobe was identified as the involved lobe instead of the right cranial lobe in 1 dog.
Histologic examination confirmed bullae as the most common cause of spontaneous pneumothorax in this study, which is consistent with previous reports.1–5 Other histopathologic findings included granulation tissue with airway dilation, granulomas, pleuritis, thromboembolism, and pneumonia, all of which have been reported as underlying causes of spontaneous pneumothorax in dogs.1–4 There were several reasons that more bullae were not confirmed via histologic examination, compared with CT. The entire resected lung tissue was submitted for analysis without identification of a specific area of interest. It was left to the discretion of the laboratory technician to identify areas that appeared abnormal and cut the sections to be read by the pathologist, so a ruptured and collapsed bulla or bleb could easily be missed. Pathologists reported the lesions but not necessarily specific information regarding bullae or blebs.
Via CT, bullae, blebs, atelectesis, and pneumothorax were the only abnormalities identified; none of the other underlying disease processes were seen. There were several reasons for these results. In humans, there is a dependent increase in lung density or attenuation in normal lung.17,19 The more severe the pneumothorax at the time of the scans, the greater the amount of lung tissue that is dependent. Also, atelectasis increases attenuation of the lung tissue. In dogs, experimental pulmonary vascular occlusion may cause an increase in lung density or attenuation.24 The increased attenuation of the lung tissue along with the speed and resolution of the scanner could have resulted in these lesions being missed. For these reasons, continuous suction should be maintained during CT scan or the thorax should be completely evacuated just prior to the start of the scan. Other limitations to this study included the small population size, retrospective nature of the study, euthanasia of 1 dog without surgery or necropsy, and limited follow-up time.
Radiography is an excellent tool for diagnosis of spontaneous pneumothorax but not for detection of bullae and blebs. Computed tomography is a more sensitive method of detecting these lesions and allows the surgeon to make a more informed choice regarding the surgical approach, but does not eliminate the requirement for a thorough exploration of the thorax.
| CT | Computed tomography |
Phillips Tomoscan CX, Phillips International, Medical Division, Eindhoven, The Netherlands.
Win Episcope, version 2.0, CLIVE, Edinburgh, UK. Available at: www.clive.ed.ac.uk/winepiscope/. Accessed Aug 2000.
Pleurovac, Teleflex Medical, Teleflex Inc, Research Triangle Park, NC.
Auto Suture TA. Premium Surgical Stapler, United States Surgical, Division of Tyco Healthcare Group LP, Norwalk, Conn.
References
- 1↑
Valentine A, Smeak D, Allen D, et al. Spontaneous pneumothorax in dogs. Compend Contin Educ Pract Vet 1996; 18: 53–62.
- 2↑
Puerto DA, Brockman DJ, Lindquist C, et al. Surgical and nonsurgical management of and selected risk factors for spontaneous pneumothorax in dogs: 64 cases (1986–1999). J Am Vet Med Assoc 2002; 220: 1670–1674.
- 3
Holtsinger RH, Beale BS, Bellah JR, et al. Spontaneous pneumothorax in the dog: a retrospective analysis of 21 cases. J Am Anim Hosp Assoc 1993; 29: 195–210.
- 4
Holtsinger RH, Ellison GW. Spontaneous pneumothorax. Compend Contin Educ Pract Vet 1995; 17: 197–210.
- 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.
- 6
Warner BW, Bailey WW, Shipley RT. Value of computed tomography of the lung in the management of primary spontaneous pneumothorax. Am J Surg 1991; 162: 39–42.
- 7
Yoshioka MM. Management of spontaneous pneumothorax in twelve dogs. J Am Anim Hosp Assoc 1982; 18: 57–62.
- 8
Kramek BA, Caywood DD, O'Brien TD. Bullous emphysema and recurrent pneumothorax in the dog. J Am Vet Med Assoc 1985; 186: 971–974.
- 9↑
Lesur O, Delorme N, Fromaget JM, et al. Computed tomography in the etiologic assessment of idiopathic spontaneous pneumothorax. Chest 1990; 98: 341–347.
- 10
Stogdale L, O'Connor CD, Williams MC, et al. Recurrent pneumothorax associated with a pulmonary emphysematous bulla in a dog: surgical correction and proposed pathogenesis. Can Vet J 1982; 23: 281–287.
- 11↑
Watanabe K, Kakitsubata Y, Kusumoto S, et al. Bullous lesions detected by computed tomography. Radiat Med 1986; 4: 119–123.
- 12↑
Carr DH, Pride NB. Computed tomography in pre-operative assessment of bullous emphysema. Clin Radiol 1984; 35: 43–45.
- 13↑
Berzon JL, Rendano VT, Hoffer RE. Recurrent pneumothorax secondary to ruptured pulmonary blebs: a case report. J Am Anim Hosp Assoc 1979; 15: 707–711.
- 14
Mittlehner W, Friedrich M, Dissmann W. Value of computed tomography in the detection of bullae and blebs in patients with primary spontaneous pneumothorax. Respiration 1992; 59: 221–227.
- 15
Sihoe ADL, Yim APC, Lee TW, et al. Can CT scanning be used to select patients with unilateral primary spontaneous pneumothorax for bilateral surgery? Chest 2000; 118: 380–383.
- 16↑
Yasufuku K, Takashi O, Fujisawa T. The effectiveness of thin-section computed tomography in diagnosing bullous lesions in patients with spontaneous pneumothorax. Nihon Kokyuki Gakkai Zasshi 1999; 37: 953–957.
- 17
Goddard PR, Nicholson EM, Laszlo G, et al. Computed tomography in pulmonary emphysema. Clin Radiol 1982; 33: 379–387.
- 18
Bergin C, Muller N, Nichols DM, et al. The diagnosis of emphysema: a computed tomographic-pathologic correlation. Am Rev Respir Dis 1986; 133: 541–546.
- 19
Kreel L. Computed tomography of the thorax. In: Kreel L, Steiner RE, eds. Medical imaging. Aylesbury, England: HM & M Publishers Ltd, 1979; 132–139.
- 20
Schwarz LA, Tidwell AS. Alternative imaging of the lung. Clin Tech Small Anim Pract 1999; 14: 187–206.
- 21
Sampietro R. Videothoracoscopic treatment of bullous lung disease: indications and techniques. Int Surg 1996; 81: 333–335.
- 22
Gupta KB, Mishra DS, Tandon S, et al. Role of chest CT scan in determining etiology of primary spontaneous pneumothorax. Indian J Chest Dis Allied Sci 2003; 45: 173–177.
- 23↑
Brissot HN, Dupre GP, Bouvy BM, et al. Thorascopic treatment of bullous emphysema in 3 dogs. Vet Surg 2003; 32: 524–529.
- 24↑
Grossman ZD, Thomas FD, Gagne G, et al. Transmission computed tomographic diagnosis of experimentally produced acute pulmonary vascular occlusion in the dog. Radiology 1979; 131: 767–769.
