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PneumothoraxIt is important to view around the periph-ery of the lungs to look for a pneumotho-rax (air in the pleural space with associatedcollapsed lung). It is very easy to miss a pneumothorax. Watch out for the following signs:

One half of the lung may seemblackerthat is, more radiolucentthan the other, which will be moreradio-opaque or whiter. In particular,the area beyond the collapsed lungwill be very radiolucent because thereare no pulmonary vessel markings.

You should be able to identify theedge of the collapsed lung (see fig 1).

Having identified a pneumothorax youneed to look for several more associatedabnormalities: Most importantlythis is a pass or fail

observationis there evidence of atension pneumothorax? This occurs

when air can enter the pleural space(via a hole in the lung surface or thechest wall) but, because of a ball-valveeffect, air cannot leave by the sameroute. So more and more airaccumulates in the pleural space.This pushes the mediastinum over tothe opposite (normal) side andeventually compresses the normallung so that less inspiration occurson the normal side, with compressionon the heart and decreased venousreturn until finally the patient arrests(see fig 2). Always look for this andsay: There is no shift of themediastinum and therefore notension pneumothorax or There is

Chest x rays made easy In the third of a five part series, Elizabeth Dick looks at abnormalities of the lung fields

The basics of looking at a chest x ray (recap):

First look at the mediastinal contoursrunyour eye down the left side of the patientand then up the right.

The trachea should be central. The aorticarch is the first structure on the left,followed by the left pulmonary artery;notice how you can trace the pulmonaryartery branches fanning out through thelung (see figure 1).

Two thirds of the heart lies on the left sideof the chest, with one third on the right.The heart should take up no more thanhalf of the thoracic cavity. The left borderof the heart is made up by the left atriumand left ventricle.

The right border is made up by the rightatrium alone. Above the right heart borderlies the edge of the superior vena cava.

The pulmonary arteries and main bronchiarise at the left and right hila. Enlargedlymph nodes can also occur here, as canprimary tumours. These make the hilumseem bulkynote the normal size of thehila on this film.

Now look at the lungs. Apart from thepulmonary vessels (arteries and veins), theyshould be black (because they are full ofair). Scan both lungs, starting at the apicesand working down, comparing left withright at the same level, just as you wouldwhen listening to the chest with yourstethoscope. The lungs extend behind theheart, so look here too. Force your eye tolook at the periphery of the lungsyoushould not see many lung markings here; ifyou do then there may be disease of the airspaces or interstitium. Dont forget to lookfor a pneumothorax.

Make sure you can see the surface of thehemidiaphragms curving downwards, andthat the costophrenic and cardiophrenicangles are not bluntedsuggesting aneffusion. Check there is no free air underthe hemidiaphragm.

Finally, look at the soft tissues and bones.Are both breast shadows present? Is therea rib fracture? This would make you lookeven harder for a pneumothorax. Are thebones destroyed or sclerotic?

Fig 1 Right pneumothorax. The right side of the lung is blacker, and the lung edge is seen (arrow). There is nomediastinal shift and therefore no tension

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shift of the mediastinum away fromthe side of the pneumothoraxindicating a (right/left) tensionpneumothorax. This is a medicalemergency which I would treatimmediately by inserting a large borecannula into the (right/left) pleuralspace.

The cause of the pneumothorax maybe apparentfor example, fracture ofthe ribs.

There may be associated surgicalemphysemathat is, air in the softtissuesand air in the mediastinum(see fig 3).

There is extra shadowing in the lungsIt may be difficult to work out what is caus-ing extra shadowing in the lungs, especial-ly near the mediastinum where normalstructures may overlay the extra shadow-ing. It is useful to look at the periphery ofthe lungs because normally the outermostedge of the lungs should be fairly blackwith a few tapering blood vessels. If you dosee more shadowing in the periphery thenthere may be either interstitial or air spacedisease. As examiners often show filmswith one of these two types of shadowing,understanding the difference betweenthese two is worth while because it will helpyou to interpret what you see and lead youto the correct differential diagnosis.

The lung is made up of bronchi, whichbranch, at the end of which are alveoli. Theinterstitial space (or potential space) sur-rounds the alveoli. The whole of the lung

from bronchi to alveoli is the air spacethat is, it normally contains air. But the air spaces can fill upwith fluid (such as insevere pulmonary oedema), with pus (asin infection), with blood (as in rare diseasessuch as Goodpastures syndrome, associ-ated with renal failure), or with tumourcells (alveolar carcinoma).

Fluid and pus are more common thanthe second two. When the air spaces fill up,the alveoli fill first, with the bronchi beingrelatively spared. Therefore the bronchi,which are still air filled, stand out againstthe alveoli, which are filled with pus orfluid. This is called an air bronchogramand is simply a sign that there is air spacedisease. Consolidation is another term forair space shadowing (see figs 4 and 5). Ifthere is air space disease then you need towork out which part of the lungs it is affect-ing. A quick way is to use the word zoneto describe which part of the lung is affect-ed. Say something like There is shadow-ing in the air spaces of the right mid andlower zone. You can then take your timeto work out which lobe is affected. You can

Fig 2 Left tension pneumothorax with shift of the mediastinum to the right. The lung edge is arrowed

Fig 3 Surgical emphysema (arrow) and pneumomediastinum (arrowhead)

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find out more about lobar anatomy in thelater section on collapse and consolidation.

Lets turn to the interstitial space. Thissurrounds bronchi, vessels, and groups ofalveoli. When there is disease in the interstitium it manifests itself by reticulo-nodular shadowing (criss cross lines ortiny nodules or both). The main twoprocesses affecting the interstitium areaccumulation of fluid (occurring in pul-monary oedema or in lymphangitis carci-nomatosa) and inflammation leading tofibrosis (occurring in industrial lung dis-ease, inflammatory arthritides such asrheumatoid arthritis, inflammation ofunknown cause such as cryptogenic fibros-ing alveolitis and sarcoidosis). If you seecriss cross lines or tiny nodules or both say:There is reticulo-nodular shadowing with-in the lower zones. (See figure 6.)

Use the table to work out whether theextra shadowing you can see is air space orinterstitial.

Next month: we will look at collapse,consolidation, and pleural effusions.

I would like to thank Dr Anju Sahdev,Dr Brian Holloway, and Dr Robert Dickfor contributing some of the films whichare illustrated.

Elizabeth Dick, specialist registrar in radiology, North Thames Deanery

Fig 5 Right middle and lower zone consolidation/airspace shadowing. Note air bronchogram (arrow). There is no loss of volume, which is a key feature ofconsolidation

Fig 6 Recticular-nodular shadowing caused by lung fibrosis (circled). Note how the heart has lost its normal smoothoutline and seems shaggy

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Erratum: see p407.

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Fig 4 Left and right lower lobe air space shadowing in an ITU patient

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Features of air space and interstitial lung disease

Air space disease Interstitial lung disease

Zones Any Any

Appearances Confluent shadowing Linear/reticular/nodular Air bronchograms shadowing

Causes Fluid (pulmonary oedema, Fluid (pulmonary oedema/(differential adult respiratory distress lymphangitisdiagnoses) syndrome) carcinomatosa)

Pus (infection/consolidation) Inflammation leading tofibrosis (industrial lung

Blood disease, inflammatory(Goodpastures syndrome) arthritides, inflammation of

unknown cause, sarcoid)Tumour cells(alveolar cell carcinoma)