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8th meeting of the radiology residents

date : 21.03.2018

Theme: Pelvis

Date: 14.04.2018г.

Place: COSMOS Coworking Camp, Angel Kanchev str. 3

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"Quality is not an act. It is a habit."


Aristotle


SPONTANEOUS PNEUMOMEDIASTINUM

date : 31.12.2015


Gavril Nakov
Elena Ruskova
Galina Kirova
Tsvetan Mintchev


Imaging Diagnostic Department, Tokuda Hospital Sofia; Thoracic Surgery Department, Tokuda Hospital Sofia; "Nikola Y. Vaptsarov" 51B, 1407 Sofia, Bulgaria

gavril_gn@yahoo.com


Keywords: pneumomediastinum, acute chest pain, subcutaneous emphysema, dyspnea, dysphagia, imaging studies


Clinical history: A 15-year-old previously healthy male patient presented in the emergency room with an onset of a continuous intensifying retrosternal chest pain after his P.E. class. He reports of difficult and painful swallowing of food at dinner the same night. The blood analysis was normal. A pericardial friction rub sound was heard on the left sternal border, 4th-5th intercostal space (Hamman’s sign).


Imaging findings:

The posteroanterior chest radiograph reveals a fine linear collection of air in the right extrapleural space paratracheally continuing down the neck and a subcutaneous emphysema under the left clavicle. A third linear air zone is seen paratracheally on the left, as well as one contouring the left pulmonary artery (fig.1). On the lateral chest radiograph apart from the already described air zones, there is such in the retrosternal and retrocardiac regions and in the middle mediastinum (fig.2). A water-soluble contrast swallow was performed - the contrast agent flows freely through the esophagus – no stenoses, dilatations or extravasation are observed (fig.3). The obtained CT shows a subcutaneous emphysema, outlining of the subclavian vessels as well as dissection of the big vessels, the trachea and the esophagus. Air is present in the anterior mediastinum in retrosternal space (fig.4). The chest X-ray performed 10 days later shows total resorption of the air in the mediastinum (fig.5).


Final diagnosis: Non-complicated spontaneous pneumomediastinum


Discussion:

Pneumomediastinum is described as the existence of free air within the mediastinum. The causes can be various and are divided in two groups – spontaneous and secondary. Secondary pneumomediastinum can be induced by: 1) blunt trauma, 2) iatrogenic (mechanical ventilation, perforation), 3) obstruction of the airways (asthma, foreign body inhalation). Spontaneous pneumomediastinum was first reported by Louis Hamman in 1939 [1]. Its incidence is 1:7000 to 1:45 000 hospital admissions. It is most common observed in young men who are tall and thin triggered by conditions such as Valsalva maneuver exercise, asthma, diabetic ketoacidosis, substance abuse, vomiting. The pathophysiological basis of the phenomenon is the Macklin effect [2]. The latter consist of rupturing of the terminal alveoli, due to an increased intrathoracic pressure, dissection of the air contiguous to the bronchovascular sheaths to the pulmonary hila and extention in the mediastinum. Clinically the pneumomediastinum is associated with the triad of chest pain, subcutaneous emphysema and dyspnea. Other symptoms include odynophagia and dysphagia, cough, fever, Hamman’s sign (systolic crackles in the left sternal border)[3], [4]. The diagnosis is confirmed by physical examination and chest radiographs (PA and LAT). Computer tomography is also necessary when pneumomediastinum is suspected but not apparent on the radiograph and to exclude other pulmonary processes [5]. The main radiographic findings in a case of pneumomediastinum consist of lucent streaks or bubbles of gas that outline mediastinal structures, e.g. 1. the mediastinal pleura making it visible; 2. the trachea; 3. the heart from the sternum on lateral view; 4. arteries (“tubular artery” sign on front view); 5. the extrapericardial (mediastinal) part of the right pulmonary artery (“ring around the artery sign” on lateral view); 6.bronchi (“double bronchial wall sign” on frontal view) 7. the brachiocephalic veins at their confluence (V sign). When gas separates the superior surface of the diaphragm from the heart on a PA chest radiograph the result is a continuous diaphragm sign. Normally on lateral view, the anterior left hemidiaphragm is obscured by contact with the heart and pericardium. In the presence of pneumomediastinum, gas between the pericardium and the diaphragm renders the anterior part of the left hemidiaphragm visible – this finding is known as the continuous left hemidiaphragm sign. Naclerio’s V sign is present when gas outlines the lateral margin of the descending aorta and extends laterally between the parietal pleura and the medial left hemidiaphragm. In infants, the manifestation of pneumomediastinum includes the elevation of thymic lobes (thymic spinnaker-sail sign) [5]. Spontaneous pneumomediastinum is a self-limiting condition. It is usually resolved after conservative management and bed rest. Oxygen therapy facilitates the absorption of free air in the meadiastinum [8].


Differential diagnosis:

Initial differential diagnosis is broad and includes conditions that present themselves with acute precordial pain from a musculoskeletal, pleural, pulmonary, cardiac or esophageal cause [7]. Some of the most common conditions that have to be excluded are acute coronary syndrome, pericarditis, pneumothorax, pneumopericardium, pulmonary embolism, tracheobronchial tree rupture and Boerhaave syndrome (esophageal rupture due to vomiting, assessed with a water-soluble contrast swallow) [6]. Radiographic differential diagnosis should exclude pneumothorax and pneumopericardium. Pneumomediastinum is presented as multiple thin lucencies of air that can extend to other parts of the mediastinum or the neck and dissect mediastinal structures. In pneumothorax there are apical lucencies when the patient is upright and basal lucencies when he is in supine position. Pathognomonic sign for pneumothorax is the deep sulcus sign. Pathognomonic sign for pneumopericardium is a broad band of lucency surrounding the heart (halo sign). Both pneumothorax and pneumopericardium do not extend outside the pleura or pericardium respectively and do not outline mediastinal structures (pneumopericardium outlines the ascending aorta and the main pulmonary artery due to the position of the pericardium). In pneumomediastinum with a change of the position of the patient the distribution of the gas does not shift its place, whereas in pneumothorax or pneumopericardium it does (within the pleura or the pericardium) [5].


Take home messages:

Pneumomediastinum and particularly a spontaneous one, should be considered as a differential diagnosis of an onset of acute chest pain, especially in previously healthy and thin young men. The pathognomonic signs of the condition on a chest X-ray help the physician to make the diagnosis fast and to distinguish it easily.


Bibliography:

1. Hamman L; Spontaneous mediastinal emphysema; Bull Johns Hopkins Hospital 1939;64:1–212. Murayama S, Gibo S; World Journal of Radiology 2014;11:850–8543. Caceres M, Ali SZ, Braud R, Weiman et al; Spontaneous pneumomediastinum: a comparative study and review of the literature; Annals of Thoracic Surgery, 2008;86:962 - 966 4. Weissberg D, Weissberg D; European Journal of Cardiothoracic Surgery 2004;5:885-8885. Bejvan SM, Godwin JD; American Journal of Roentgenology 1996;5:1041-10486. Meireles J, Neves S, Castro A, França M; Respiratory Medicine, 2011;4:181-1837. Ralph-Edwards AC, Pearson FG; Atypical presentation of spontaneous pneumomediastinum, Annals of Thoracic Surgery, 1994;58:1758-1760 8. Patel A, Kesler B, Wise RA; Chest 2000;117:1809-1813



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