Subcutaneous Emphysema, Pneumomediastinum, and Pulmonary Emphysema in a Young Schipperke

Case Report

A 4-month-old, intact female schipperke was referred to the Purdue University Veterinary Teaching Hospital (PUVTH) for evaluation and treatment of subcutaneous (SC) emphysema of 3 days’ duration. The SC emphysema was first noted by the owner 1 day after routine vaccinations were given. The owner reported a dry, nonproductive, honking cough of 1 week’s duration that had acutely progressed to paroxysmal episodes every few hours after the SC emphysema was noted. The SC emphysema was initially confined to the cranial left thoracic inlet region and progressed over the next 24 hours to include the entire thoracic and ventral abdominal regions, despite restricted activity. Carprofen (3.7 mg/kg body weight, per os [PO] bid) was prescribed by the referring veterinarian. No clinical improvement was noted.

Upon admission to PUVTH, extensive SC emphysema was evident, but no respiratory distress was noted. During examination, a dry, non-productive, honking cough was noted both during excitement and after tracheal palpation. No external wounds or evidence of trauma were noted. The owner reported no history of trauma, although the patient did have a propensity to chew wood and other foreign objects.

Oropharyngeal examination was performed, and no lesions were noted. A complete blood count showed no significant abnormalities. A biochemical profile was not performed. Thoracic radiographs showed diffuse SC emphysema and pneumomediastinum, but no evidence of pneumothorax [Figures 1, 2]. No evidence of pneumoretroperitoneum was observed on abdominal radiographs. An esophagram using iodinated water-soluble contrast media was also performed, and no abnormalities were detected.

Initial treatment at PUVTH included strict cage confinement and observation for respiratory distress and circulatory compromise secondary to the pneumomediastinum. Despite cage confinement, girth measurements indicated progression of the SC emphysema. No further paroxysms of coughing occurred. Reevaluation of thoracic radiographs on days 3 and 5 confirmed a worsening of the SC emphysema. No progression of the pneumomediastinum was noted, and a mild pneumothorax developed on the right hemithorax. Fecal examination using qualitative and zinc sulfate flotation, as well as Baerman techniques, was performed to investigate the possibility of parasitic lung disease resulting in pneumomediastinum. These tests were negative. On day 7, tracheoscopy and esophagoscopy were performed under general anesthesia. No abnormalities were visualized. In order to further investigate the possibility of an airway perforation as the cause for the pneumomediastinum and SC emphysema, a tracheogram and bronchogram were performed under direct fluoroscopic observation. Iodinated water-soluble contrast medium was used, and the patient was rotated to allow the contrast media to fully coat the larger airways. No tracheal or bronchial defects were evident.

Exploratory surgery was performed on day 8, because no obvious cause for the pneumomediastinum was found, and the SC emphysema was worsening. Under general anesthesia, the patient was placed in dorsal recumbency, and the cervical region was explored first. After isolating the trachea, the cervical region was flooded with warm, sterile saline, and positive-pressure ventilation was performed to investigate for any air leakage from the trachea. No defects were found in the cervical trachea. The esophagus was visually inspected, and no defects were identified. A median sternotomy was then performed, since no source of air leakage was identified. The right middle lung lobe appeared to be emphysematous, with bullae on the surface. The thoracic cavity was filled with warm, sterile saline, and subsequent positive-pressure ventilation failed to establish a source for the leakage of air. As the emphysematous right middle lung lobe was suspected to be the cause of the pneumomediastinum and SC emphysema, a complete lobectomy of the right middle lung lobe was performed. A regional lymph-node biopsy was also performed. Lung and lymph-node tissue samples were submitted for bacterial and fungal cultures as well as histopathological evaluation. Before closing the sternotomy site, the thoracic cavity was flooded with warm, sterile saline, and positive-pressure ventilation was performed to confirm no leakage of air from the lobectomy site. A thoracostomy tube was surgically placed to facilitate the removal of air in the pleural space postoperatively.

The SC emphysema decreased slightly in the first 24 hours postoperatively but significantly decreased over the next 6 days. A small amount of air and 65 mL of a serosanguinous fluid were aspirated from the thoracostomy tube in the first 24 hours after surgery. By day 7, the amount of fluid aspirated from the thoracostomy tube decreased to <2.2 mL/kg body weight, which was the amount expected from the presence of the tube itself. The thoracostomy tube was removed 8 days after surgery. No complications such as ascending infection or tube malfunction occurred.

Histopathological evaluation of the pulmonary tissue revealed marked pulmonary emphysema of unidentified etiology [Figure 3]. Congestion, mild pulmonary edema, and a mixed-cellular, interstitial pneumonia with fibrosis were detected. The presence of all normal pulmonary parenchymal structures, the relatively normal distribution/orientation of these structures, and the lack of obvious hypoplastic or prominent inflammatory changes suggested a probable congenital condition. Histopathological evaluation of the lymph node showed mild, reactive hyperplasia. Bacterial cultures of the pulmonary tissue grew Bordetella bronchiseptica (B. bronchiseptica). Therapy with amoxicillin/ clavulanic acid (15.6 mg/kg body weight, PO bid) was initiated for a 2-week period, based on antibiotic sensitivity results. Two months after initial presentation, the dog was clinically normal on recheck examination. Recurrence of the pneumomediastinum or SC emphysema was not found radiographically.

Discussion

Pneumomediastinum is the presence of free air or gas within the confines of the mediastinum. The mediastinum, considered incomplete in dogs, is a potential space located centrally between the left and right pleural cavities and contains numerous vital structures including the heart, trachea, esophagus, great vessels, lymphatics, vagus nerves, and thymus. The mediastinum communicates cranially with the cervical fascial planes through the thoracic inlet and with the retroperitoneal space through the aortic hiatus.^1–4

Pneumomediastinum can result from a variety of defects in the airways, lung, oropharynx, esophagus, retroperitoneal space, or fascial planes of the neck. Pneumomediastinum can also result from blunt or penetrating wounds, infection with gas-forming organisms, or iatrogenic injuries such as traumatic intubation, endotracheal tube cuff overinflation, positive-pressure ventilation, transtracheal wash procedures, esophageal dilatation, and jugular venipuncture. In a review of 17 dogs with pneumomediastinum, nine were trauma induced, two were associated with acute vomiting, and two were iatrogenic.⁴ In four of the 17 (23.5%) cases, the etiology was undetermined.⁴ Spontaneous pneumomediastinum was also reported in a group of racing greyhounds.⁵

Pneumomediastinum in the dog reported here probably resulted from the pulmonary emphysema noted on histopathological evaluation of the lobectomized lung lobe. An increase in intra-alveolar pressure or a decrease in perivascular interstitial pressure can create a gradient that leads to alveolar rupture. Preexisting pulmonary parenchymal disease predisposes an individual to alveolar disruption.⁶ If air from the ruptured alveoli enters the perivascular or peribronchial adventitia, the pressure difference between the mediastinum and the peripheral lung parenchyma forces the air to dissect along the peribronchial connective tissues and eventually to the mediastinum. Because the cranial portion of the mediastinum is continuous with the cervical fascial planes, extension of free air from the mediastinum to the SC tissues can occur. Increased mediastinal pressure due to the presence of free air or gas can also rupture the mediastinal pleura, causing pneumothorax. Pneumothorax and SC emphysema secondary to pneumomediastinum have been described in humans with bronchial asthma, dermatomyositis, trauma, isolated Valsalva maneuvers, and multiple forms of pulmonary disease such as chronic obstructive pulmonary disease.^7–9 Pulmonary emphysema secondary to rupture of alveolar walls is thought to result from a form of valvular obstruction in a regional bronchus. Inspired air enters the pulmonary parenchyma but is unable to escape even with forced expiration. As the alveoli fill with air, the pressure increases and eventually the alveoli rupture.^10–12 Valvular obstruction of bronchi can occur with a mucous plug or a structural defect in the bronchi.

Congenital pulmonary emphysema, similar to that seen in human infants, has rarely been reported in the dog.^101113–15 In humans, three pathological groups have been described. In one group, a defect in the development of bronchial cartilage allows bronchi to collapse during expiration. In a second group, external compression of bronchi, usually from an abnormally positioned blood vessel, causes the small airway collapse. The third group are idiopathic cases.¹⁰¹¹ Common presenting complaints in both human infants and dogs include progressive dyspnea and cyanosis. Radiographs typically show hyperlucent areas in the pulmonary fields with displacement of the mediastinum, diaphragm, and cardiac silhouettes.^10111314 None of the reported cases of congenital pulmonary emphysema^101113–15 in the veterinary literature had an association with pneumomediastinum or SC emphysema, as was seen in the young schipperke of this report. Histopathological findings in some of the cases of congenital pulmonary emphysema reported in dogs showed an absence of, or decrease in, bronchial cartilaginous tissue or a decrease in elastin around the alveolar capillaries.^1013–15 These histopathological findings were not noted in the dog reported here. Histopathological findings in other cases of canine congenital pulmonary emphysema¹⁰¹¹ only revealed emphysematous changes in the pulmonary tissue, as was the situation in the dog reported here.

The role of B. bronchiseptica infection in the case of this study is unclear. Bordetella bronchiseptica, a highly infectious, gram-negative coccobacillus, is one of the principal agents of canine infectious tracheobronchitis.¹⁶ In humans, the Valsalva maneuver, a forceful expiratory effort against a closed glottis, has been associated with pneumomediastinum and SC emphysema.⁶ Coughing can be considered a Valsalva maneuver. The paroxysmal coughing typical of B. bronchiseptica infection could result in pressure-gradient changes that lead to the development of ruptured alveoli and subsequent pneumomediastinum. However, the lack of prominent inflammatory changes in the face of significant pulmonary emphysema in the affected lung lobe of the dog reported here limits the significance of the Bordetella isolate in the development of the pulmonary lesions noted.

Primary pulmonary pathology should be considered in cases of SC emphysema and pneumomediastinum even when no obvious radiographic lesions are noted in the pulmonary tissues. Superimposed, spurious shadows caused by SC emphysema can confound accurate evaluation of deeper pulmonary structures. Few cases of emphysematous pulmonary disease in young dogs have been reported in the veterinary literature. This may occur more commonly than reported, but the condition is not recognized since symptoms may develop only later in life. To the authors’ knowledge, there are no reports of spontaneous pneumomediastinum and SC emphysema in dogs with congenital pulmonary emphysema. The presenting complaints in the few reports of congenital pulmonary emphysema in dogs are generally progressive dyspnea and cyanosis. This case may represent a variation of congenital pulmonary emphysema not yet reported in dogs and is best identified as idiopathic congenital pulmonary emphysema.

Spontaneous pneumomediastinum in both humans and veterinary patients is generally benign and self-limiting. Therefore, pneumomediastinum is usually treated conservatively, with spontaneous resolution occurring over a 2-week period.^15–79 In the dog presented here, a progression in the degree of SC emphysema prompted a search for an active source of the mediastinal air. In cases such as this, exploratory thoracotomy may be both diagnostic and therapeutic.

Based on the age of the dog in this report and the histopathological features of the affected lung lobe, congenital pulmonary emphysema is the probable underlying cause of the pneumomediastinum with development of subsequent SC emphysema. The B. bronchiseptica isolated from the affected lung lobe was considered secondary or incidental. There is no significant histopathological support for Bordetella pneumonia. However, the paroxysmal coughing typical of B. bronchiseptica reported by the owner may have contributed to the development of the pneumomediastinum from the pulmonary lesions. Alternatively, coughing secondary to the pulmonary lesions may have led to the development of the pneumomediastinum.

Conclusion

The progression in the degree of SC emphysema in the dog presented here prompted a search for an active source of mediastinal air. When no source was identified using less invasive measures, exploratory thoracotomy revealed significant pulmonary emphysema in the right middle lung lobe of this patient. Removal of the affected lung lobe resulted in resolution of the SC emphysema and pneumomediastinum. Because spontaneous pneumomediastinum is generally considered benign and self-limiting, patients are usually treated conservatively. In cases of spontaneous pneumomediastinum that do not respond to conservative therapy, primary pulmonary pathology should be considered. Surgical intervention may be both diagnostic and therapeutic for spontaneous pneumomediastinum that does not respond to conservative therapy.

Histopathological findings in this young dog showed relatively normal orientation of pulmonary structures in the face of diffuse pulmonary emphysema with no obvious specific etiology, which supports a diagnosis of idiopathic congenital emphysema in this dog. To the authors’ knowledge, this is the first report of congenital pulmonary emphysema resulting in pneumomediastinum and SC emphysema in a dog.

Acknowledgment

The primary author wishes to thank Dr. Lynn Guptill for her support during the preparation of this manuscript.