pNEUMOMEDIASTINUM

1. pNEUMOMEDIASTINUM The case of Snoop Dogg 143380

2. Dogs • Entrance of gas to the mediastinum • Dissection along fascial planes of the neck, (deep penetrating wound, including iatrogenic) • Dissection along peritracheal sheath, bronchi, or esophagus in cases of penetration • Dissection of air from ruptured alveolar bases adjacent to blood vessels with tracking along adventitial tissue spaces • Ascending from the abdomen; particularly the retroperitoneal space (both peritoneal and retroperitoneal sources have been documented in humans) Suter PF. Thoracic Radiography. A Text Atlas of thoracic Diseases of the Dog and Cat. PF Suter, Wettswil, Switzerland, 1984.

3. Alveolar rupture • Sudden increase in alveolar pressure, or fall in perivascular interstitial pressure causes a gradient that disrupts base of alveolus and air is introduced into the interstitium • Most commonly associated with an increase in transpulmonary pressure (not just intrapulmonary pressure) • Penetrates bronchovascular sheath and becomes interstitial emphysema which can progress • Air moves centripetally, pumped by the action of breathing so most dramatic centrally Park, DR, Vallieres, E (2005) Pneumomediastinum and Mediastinitis. Murray, JF Nadel, JA eds. Textbook of respiratory medicine 4th ed. ,2039-2049 Saunders New York, NY

4. Dogs • Causes of pneumomediastinum • Blunt trauma-bronchial or rupture of alveolar basement membrane • Perforating injury to neck or trachea (including iatrogenic) • Anesthesia; excessive positive pressure/ETT • Esophageal rupture • Spontaneous (cough, respiratory distress, emphysema, foreign bodies, bronchitis, bronchiolitis) • Lung lobe torsion with bronchial rupture • Idiopathic pneumomediastinum-usually resolves rapidly • Suter says that pneumomediastinum cannot be caused by pneumothorax… But may result in it! Suter PF. Thoracic Radiography. A Text Atlas of thoracic Diseases of the Dog and Cat. PF Suter, Wettswil, Switzerland, 1984.

5. Dogs • Radiographic features • Diminished opacity • Gas outlining of mediastinal structures • Shadows around trachea and esophagus tracking into the fascial planes of the neck • Subcutaneous emphysema of the neck, head, and body • Dissecting along aorta into retroperitoneal spaces; outlining kidneys • Elevation of cardiac silhouette off sternum Suter PF. Thoracic Radiography. A Text Atlas of thoracic Diseases of the Dog and Cat. PF Suter, Wettswil, Switzerland, 1984.

6. Dogs • Sequelae • May cause respiratory signs, exercise intolerance, crepitus, subcutaneous emphysema • Regression usually in 2- 10 days • Severe cases: • Mediastinal rupture may cause pneumothorax • Pneumomediastinum may impede venous return to heart and cause cardiovascular collapse Suter PF. Thoracic Radiography. A Text Atlas of thoracic Diseases of the Dog and Cat. PF Suter, Wettswil, Switzerland, 1984.

7. Humans… • Spontaneous pneumomediastinum • Associated with precipitating events that cause a strong Valsalva maneuver (forcible exhalation against a closed glottis) • Secondary pneumomediastinum • Trauma-esophageal, tracheobronchial, etc • Tissue dissection from a spontaneous pneumothorax • Infection, pulmonary or mediastinal • More likely to have higher presence of clinical and radiographic signs than spontaneous pneumothorax • Symptoms • Chest pain • Dyspnea • Cough • Subcutaneous emphysema Caceres M, Ali, SZ, Braud, R, et al. Spontaneous pneumomediastinum: A comparative study and review of the literature. Ann ThoracSurg 2008; 86: 962-966.

8. Humans… • Triggering events in spontaneous pneumothorax • Emesis-36% • Asthma exacerbation-21% • Cough-7% • Others-physical activity, defecation, choking episodes, childbirth, intense screaming, inhalational drugs (like helium, marijuana…) • Idiopathic-21% Caceres M, Ali, SZ, Braud, R, et al. Spontaneous pneumomediastinum: A comparative study and review of the literature. Ann ThoracSurg 2008; 86: 962-966.

9. Humans… • Treatment • Treat underlying cause/source • Specific treatment rarely needed • Oxygen therapy may aid in the reabsorption of the subcutaneous emphysema by replacing nitrogen gas with oxygen for more rapid reabsorption • Decompression if causing cardiovascular signs • Pneumopericardium can be rapidly life-threatening

10. Snoop Dogg • 5 yo MN Miniature Pinscher • Presents for tachypnea , dyspnea, inappetance of 1 week duration. Initially the RDVM prescribed meloxicam and sucralfate. Vomited 2x after medication. After 1 week, with no change in signs, RDVM took radiographs documenting abdominal gas (site unknown). Performed reportedly normal barium study and referred to NCSU. • No history of trauma, foreign body ingestion, or being unattended outside. • PE-Quiet lung sounds ventrally, severe crepitus, tachycardic, normothermic.

11. Radiographs

12. More diagnostics • CBC-mild mature neutrophilic leukocytosis (previously normal at RDVM). Lymphopenia, monocytosis. • CT findings-143380 • Possible alveolar disease • Perivascular air suggesting interstitial air leak • Pneumomediastinum and pneumoretroperitoneum • Mild pneumoperitoneum and subcutaneous gas • BAL-chronic suppurative inflammation!

13. 1944, Macklin and Macklin • “air passing through numerous minute ruptures in the strained bases of the alveoli of the overinflated region into the underlying vascular sheaths. The air bubbles…moved along the vascular sheaths, coalescing and gaining in size. This streaming of air through the pulmonic interstitium reminded one of the flow of a river that ever increases in size by the addition of new tributaries as it proceeds on its course. Reaching the root of the lung, the train of air bubbles passed into and distended the mediastinum.”

14. Snoop Dogg • Discharged on antibiotics • Final thoughts… Pneumomediastinum secondary to alveolar rupture? Associated with pneumonia? Vomiting episode?

15. References • Suter PF. Thoracic Radiography. A Text Atlas of thoracic Diseases of the Dog and Cat. PF Suter, Wettswil, Switzerland, 1984 . • Park, DR, Vallieres, E (2005) Pneumomediastinum and Mediastinitis. Murray, JF Nadel, JA eds. Textbook of respiratory medicine 4th ed. ,2039-2049 Saunders New York, NY • Caceres M, Ali, SZ, Braud, R, et al. Spontaneous pneumomediastinum: A comparative study and review of the literature. Ann ThoracSurg 2008; 86: 962-966. • Zaia, BE, Wheeler, S. Pneumomediastinum after inhalation of helium gas from party balloons. Journal of Emergency Medicine, 2007.