Ecr Pneumomed

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Radiologic features of pneumomediastinum: from classicsigns to clinical management

Poster No.: C-2405

Congress: ECR 2015

Type: Educational Exhibit

Authors: L. A. Ferreira, M. Barros, J. F. Costa, F. Caseiro Alves; Coimbra/ PT

Keywords: Mediastinum, Thorax, Digital radiography, CT, Education, Acute,Outcomes

DOI: 10.1594/ecr2015/C-2405

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Learning objectives

• Review the mediastinic anatomy with radiologic correlation.• Review and illustrate different etiologies of pneumomediastinum• Illustrate radiologic features of pneumomediastinum, including typical

radiographic signs that assist diagnostic.

• Discuss the role of plain radiography and computed tomography (CT) onevaluation and clinical management.

Background

The mediastinum is comprehends the space between the two pleural cavities, containingall thoracic organs excepting the lungs.

It is anatomically bordered anteriorly by the sternum, posteriorly by dorsal vertebralcolumn, laterally by pleura l cavi ties, superiorly by thoracic inlet and inferiorly by thediaphragm. For anatomical purposes it is divided in four compartments, the superiormediastinum that comprehend the mediastinum from the thoracic inlet until a virtual linedrawn from the manubriosternal joint to the intersomatic space of T4-T5; and the anterior,medial and posterior mediastinum according to relative position to the heart, pericardiumand great vessels, that are comprised in the medial mediastinum. Radiologists usuallyfollow the Felson or Zylak methods and divide the mediastinum in three compartments,which are delimited by virtual lines. According to Felson in the lateral chest radiogram animaginary line that goes from thoracic inlet to the diaphragm along the heart and anteriorlyto the trachea separates the anterior from the medial mediastinum, being the posteriordelimited from the medial mediastinum by another imaginary line formed by connectingdots located one centimeter posteriorly to the anterior margin of vertebral bodies Fig. 1 onpage 2 . The Zylak method is similar to the anatomical division, without the superiormediastinum Fig. 2 on page 3 .

The mediastinum contains several anatomic structures, namely the thymus, heart,pericardium, great vessels, trachea, esophagus, thoracic duct and many nervoussystem components. Although the mediastinum is located in the thorax several

anatomic structures pass through it, creating continuity/communication with, for instance,submandibular space, retropharyngeal space, vascular sheath superiorly and also withretroperitoneum through peri-esophageal and peri-aortic fascial planes.

Images for this section:


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Fig. 1: Mediastinum division according to Felson method. A - anterior mediastinum; M -middle mediastinum; P - posterior mediastinum.


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Fig. 2: Mediastinum division according to Zylak method. A - anterior mediastinum; M -middle mediastinum; P - posterior mediastinum.


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Findings and procedure details

The presence of extra-luminal air in the mediastinum is not physiologic, it is calledpneumomediastinum or mediastinal emphysema. It might be caused by a broad spectrumof thoracic and extra-thoracic factors.

Intra-thoracic causes includes spontaneous pneumomediastinum associated toincreased airway pressure and might be associated also to asthma Fig. 3 on page 7, vomiting, labor, weight-lifting, valsalva against close glottis. External trauma also maycause alveolar rupture that can lead to air leak into the mediastinum.

Extra-thoracic causes may lead to accumulation of air within the mediastinumthrough dissection of the aforementioned fascial planes, for instance during dentalextraction, sinus fracture or even abdominal hollow viscos perforation whichpneumoretroperitoneum may dissect superiorly to the mediastinum.

Medical activity can cause pneumomediastinum, such as tracheostomies, trachealperforation during bronchoscopy Fig. 4 on page 8 Fig. 5 on page 8 ,mechanical ventilation, esophageal perforation during endoscopy, placement of centrallines, biopsies, among others.

The diagnosis of pneumomediastinum is essentially radiological. Chest radiograph isone of the most frequently performed exams, and one of the essential to diagnosesuch condition. The presence of extra-luminal air within the mediastinum has someradiographic features, namely contour outline of anatomic structures by air seen as lucentlines. A lucent line around the left heart border is a very commonly recognized sign Fig.3 on page 7. Some of the radiographic features are so characteristic that are classicsigns:

• Tubular Artery Sign is the outline by air of aortic arch branches seen onpostero-anterior chest radiography, that happens when air dissects frommediastinum through fascial planes to the neck Fig. 3 on page 7 .

• Continuous Diaphragm Sign represents a lucent line that outlines thepericardium from the diaphragm, turning the medial portion of the diaphragmvisible Fig. 6 on page 9 . This sign is shared with pneumopericardium,

and may be difficult to distinguish when present alone.• Naclerios's V sign corresponds to a V shape lucency composed by theoutline by air of the descending aorta and left diaphragmatic dome, onpostero-anterior chest radiogram Fig. 7 on page 10 . This particular signis frequently associated to esophageal perforation.

• Pneumoprecardium is the presence of air between the sternum and theheart, seen on lateral radiograph Fig. 8 on page 11 .


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• Ring around artery sign is the outline of hilar vessels by air seen on lateralchest radiograph.

• Spinnaker Sail Sign is seen on neonatal postero-anterior chestradiograph when thymic lobes are displaced laterally by air resembling aspinnaker sail, it's also called angel wing sign. It's a very typical sign ofpneumomediastinum in neonatal age.

Presence of subcutaneous emphysema Fig. 9 on page 12 is many times associatedwith pneumomediastinum, being a good positive predictor factor, and when the firstis present the latter should be sought. Chest radiograph also allows evaluation of thepresence of abnormal exta-luminal air concomitantly with pneumomediastinum, such aspneumothorax or pneumopericardium Fig. 10 on page 13 . Although it is the firstexam to perform sometimes chest radiographs fail to clearly state the presence of apneumomediastinum. In such cases additional studies might be needed, like CT, whichcan be useful also to clarify the source of air.

Extra-luminal air within the mediastinum may dissect superiorly through theaforementioned fascial plans and accumulate in several places in the head and necklike the retropharyngeal space Fig. 11 on page 14 Fig. 12 on page 15 orretromandibular space for instance.

There are some entities that might difficult the radiographic diagnosis ofpneumomediastinum, because t hey sh are the same etiology or even radiologicfeatures. Distinguish a pneumomediastinum from a medial pneumothorax or even apneumopericardium Fig. 10 on page 13 are some examples. Pneumopericardium isthe presence of air within the pericardic sac, on postero-anterior chest radiograms it will

appear as a lucent line surrounding the heart border that do not extend superiorly to theemergence of the great vessels Fig. 10 on page 13 and that quickly shifts with patientposition. However if air is collected inferiorly to the heart it can originate the continuousdiaphragm sign, the one it shares with pneumom ediastin um Fig. 6 on pag e 9 .

In the absence of others sources of air, medial pneumothorax may be difficult todistinguish from pneumomediastinum Fig. 13 on page 16 , it may be useful to repeatthe radiograph with patient in another position since a shift of extra-luminal air position willbe suggestive of a pneumothorax where a maintenance will be of a pneumomediastinum,or in case radiograms fail to be conclusive a CT may be performed Fig. 14 on page 17 .Other examples difficult to distinguish between pneumomediastinum and pneumothoraxare when extra-luminal air collects over the pulmonary apexes, along the diaphragm orin a subpulmonary location.


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Sometimes normal anatomic structures may give the impression of the existence of extra-luminal air within the mediastinum, namely anterior junction line and the great fissure,mainly if the radiograph is taken in a somewhat lordotic incidence.

Medical devices may simulate pneumomediastinum, namely gas containing intra-aorticballoons may give the impression that air is present within the mediastinum. An opticillusion named Mach band is characterized by a lucent line adjacent to a dense convexstructure, it may simulate a pneumediastinum when it surround the heart border forinstance Fig. 15 on page 18 , the lack of a dense line typical on the latter can helpto distinguish them.

Clinical management of pneumomediastinum will mainly depend on the underlyingcause. Most pneumomediastinum are self-limiting and will resolve with conservativetreatment, given that there is no active source of air. In case of pneumomediastinum dueto trauma or perforation surgery might be needed.

Images for this section:


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Fig. 3: Postero-anterior chest radiogram of young patient with asthma that presentedwith sudden chest pain. There are present several typical signs of pneumomediastinum,namely dissection by air of an aortic branch, called Tubular Artery Sign (white arrows);dissection of the border of the descending aorta (black arrows); dissection of mediastinalpleura around aortic arch (white arrowhead) and around heart (black arrowhead).

Fig. 4: CT scan showing pneumomediastinum due to a iatrogenic traqueal perforation(arrowhead).


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Fig. 5: Volume rendering of the CT study of the patient of figure 4 where traquealperforation can be seen on it's full extension (arrow)


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Fig. 7: Postero-anterior chest radiogram where signs of pneumomediastinum are presentincluding the classic Naclerio's V sign. This sign consists in the lucent line of the airdissection of the descending aorta, forming one limb of the V (white arrow), which together

the lucent line of air above the left diaphragm dome, forming the second V limb (blackarrow), resemble a V.


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Fig. 8: Lateral chest radiogram showing the presence of air between the sternum andthe heart (*), a pneumoprecardium.


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Fig. 9: Frontal chest radiography showing subcutaneous emphysema (arrow) associatedto pneumomediastinum.


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Fig. 10: CT topogram showing a lucent line that delineates the heart (arrows) but doesnot extend superiorly to the great vessels, a case of pneumopericardium.


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Fig. 11: Cervical lateral radiogram of a patient with pneumomediastinum. There ispresence of air in the retropharyngeal space (*) that dissected the fascial planes fromthe mediastinum to the neck.


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Fig. 12: Coronal CT reconstruction showing air dissecting from the mediastinumsuperiorly to the neck (arrows).


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Fig. 13: Postero-anterior chest radiogram showing subcutaneous emphysema(arrowhead), air dissecting neck tissues (black arrow) and a lucent line on the left borderof the heart (white arrow). This findings suggest the presence of a pneumomediastinum,

a CT was performed (Fig. 14) and revealed a concomitant medial pneumothorax, acondition difficult to distinguish from pneumomediastinum.


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Fig. 14: CT study of the same patient of figure 13 showing a medial pneumothorax (*)


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Fig. 15: Normal chest radiogram where a lucent line can be discern in the left heart border(arrows), a case of Mach band effect, mimicking a pneumomediastinum.


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Conclusion

Pneumomediastinum is a medical condition that should be quickly identified on plainradiography in order to achieve an adequate clinical manage, although in

many cases CT characterization is performed.

The radiologist should have a solid knowledge of the normal mediastinal anatomy, aswell be able to recognize the direct and indirect radiologic signs of presence of air withinthe mediastinum to be able to correctly diagnose a pneumomediastinum.

Personal information

Serviço de Imagem Médica

Centro Hospitalar e Universitário de CoimbraPraceta Prof. Mota Pinto3000-075 Coimbra

Portugal

References

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• Hammond, D. I. The "ring-around-the-artery" sign in pneumomediastinum. J.Can. Assoc. Radiol. 35, 88-9 (1984).

• Levin, B. The continuous diaphragm sign. A newly-recognized sign ofpneumomediastinum. Clin. Radiol. 24, 337-8 (1973).

• Lillard, R. L. & Allen, R. P. The extrapleural air sign in pneumomediastinum.Radiology 85, 1093-8 (1965).

• MARCHAND, P. The anatomy and applied anatomy of the mediastinalfascia. Thorax 6, 359-68 (1951).

• Meireles, J., Neves, S., Castro, A. & França, M. Spontaneouspneumomediastinum revisited. Respir. Med. CME 4, 181-183 (2011).

• MOSELEY, J. E. Loculated pneumomediastinum in the newborn. A thymic"spinnaker sail" sign. Radiology 75, 788-90 (1960).


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• Sandler, C. M., Libshitz, H. I. & Marks, G. Pneumoperitoneum,pneumomediastinum and pneumopericardium following dental extraction.Radiology 115, 539-40 (1975).

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on clinical experience of 25 cases. Respir. Med. 102, 1329-34 (2008).• Whitten, C. R., Khan, S., Munneke, G. J. & Grubnic, S. A Diagnostic

Approach to Mediastinal Abnormalities. RadioGraphics 27, 657-671 (2007).• Zylak, C. M., Standen, J. R., Barnes, G. R. & Zylak, C. J.

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