11 - paediatric chest imaging (1)

8/7/2019 11 - Paediatric Chest Imaging (1)

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Paediatric Chest Imaging


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The initial assessment of the paediatric CXRshould include:

1) Technique of the exam, to include patientpositioning, proper exposure and the degree ofinspiration

2) Position of all tubes and lines and evaluation forpneumothorax, pneumomediastinum, andpneumoperitoneum

3) Mediastinal and cardiac silhouettes4) Airway and lungs

5) Pulmonary vascular pattern

6) Abdomen


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Inspiratory Expiratory


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Chest Tubes and Catheters.


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An essential part of the assessment of the

neonatal chest x-ray includes identification ofthe position of the various tubes.

Endotracheal tubes (ETT).

Nasogastric tubes (NGT). Central venous lines.

Umbilical venous catheters.

Umbilical arterial catheters.


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Endotracheal tube (ETT)

Is clearly recognized in the midline in theneck and upper chest as it has an opaquewall.

Ideally the tip of should lie between C7 andT4, 1.2cm below the vocal cords, or 2cmabove the level of carina.

The position can change considerably withhead movement, ,so when the tube is nearT4 it could be displaced into the right mainbronchus.


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Nasogastric tube (NGT):

Is seen in the stomach, it should not be

positioned at the gastro-oesophageal junction

or above for fluid will reflux into the

oesophagus with a risk of aspiration.


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Central Venous Line

The central venous line is usually inserted

either through:

(i) the subclavian vein to the

brachiocephalic vein and then superior vena cava

(SVC); or

(ii) the internal jugular vein into the

brachiocephalic vein and into the SVC.


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Umbilical Venous and

Arterial Catheters


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Umbilical arterial catheter (UAC)

The umbilical artery is a direct continuation ofthe internal iliac arteries, thus; the catheter is

recognized by the characteristic loop formedby its entry position into the umbilicus from itloops down into the pelvis to join to theinternal iliac artery before passing into the

common iliac artery and aorta.


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Two potential positions:

*High: T4/6T9/10 ( above the diaphragm), preferredposition

*Low: L3-L4 (above the aortic bifurcation/L4-L5)

Too low a position should also be avoided to preventcomplications of bowel or renal ischaemia, which may occur ifthe catheter is between T12 and L2.

The spinal arteries are at the level of L1-L4.

The superior mesenteric artery T12-L2.

The renal arteries at L1.


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The umbilical venous catheter (UVC)

The UVC passes straight from the umbilicus

through the intrahepatic portion of the

umbilical vein, through the ductus venosus

into the IVC and thus to the right atrium.

Ideally the tip should be maintained at the

IVC/RA junction at T8-T9, but this position ishard to be achieved.


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Another important feature to recognize in the

paediatric chest is the normal thymic tissue in

the anterior mediastinum. Normal thymic

tissue, should not be confused with amediastinal or pulmonary mass.

Thymus gland


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The thymus is normally prominent on chest filmsduring the first few years of life.

Less noticeable after 3-4years of ages.

It is clearly visible to the right or left or on both sidesof the mediastinum

The usual limits in young children are from the level

of the left brachiocephalic vein to the level of thepulmonary arteries inferiorly. It may, however,extend into the neck and down to the level of thediaphragm in young infants.

In the right chest it often has a typical sail shapewith a horizontal lower border and an outer border

parallelling the chest wall. It frequently abuts anteriorribs leading to an undulating appearance.


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The normal thymus is not typically very radio-opaque but it usually permits visualization of

pulmonary vessels through it, it does notcompress the airway or adjacent vasculature.In most neonates, temporary thymicinvolution is seen during episodes of acute

illness. Thymic rebound or regrowth is oftenseen after recovery from a severe illness orafter chemotherapy.


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Pneumothorax,

Pneumomediastinum,Pneumopericardium


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The presence of free air either in the chest orabdomen is a frequent complication ofdisease and therapy in the neonatal setting.

All exams should be thoroughly scrutinizedfor the presence of pneumothorax,pneumomediastinum, or pneumoperitoneum.

A decubitis CXR, with the side of interestupright, should be obtained to evaluate for apneumothorax.

If the child cannot be positioned for thedecubitis exam then a cross table lateralchest XR.


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Pneumothorax occurs spontaneously in a few

newborn infants, more commonly occurs as a

complication of ventilator therapy in hyaline

membrane disease.

Classically a pneumothorax appears as an

area of radiolucency between the edge of the

lung and the chest wall and absence of lungmarkings peripherally.


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In neonates the signs are more subtle, the

side of the chest with the pneumothorax ismore radiolucent than the normal side, theedge of the mediastinum and sometimes thediaphragm may be more sharply defined than

normal, this is the so called etched heartborder sign, and is due to interposition of airin the pleural cavity between the heart andlung giving a clear outline. The air sometimes

causes elevation of the thymus gland fromthe mediastinum giving the appearance ofangel wings. The hyperlucent costophrenicangle is known as the deep sulcus sign.


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Air in the mediastinum is an occasionalcomplication of a pneumothorax. Andappears as a band of decrease attenuation

against the heart. It can extend over thediaphragm between the two layers of pleuraand can extend up into the neck.

Air in the pericardium has a similar

appearance but is restricted by the reflectionsof the pericardium rather than the wholemediastinum outline.


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Meconium Aspiration


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9% of term infants pass meconium around the time

of delivery. 56% of them have evidence of

meconium in the trachea, 20% develop clinicalsymptoms.

When meconium is aspirated and inhaled into the

distal airways it acts as a ball valve, causing air

trapping and a predisposition to air leaks. It causesa pneumonitis and acts as a culture medium of

secondary infection. The resultant hypoxia and

vasospasm predispose to pulmonary hypertension

and persistent foetal circulation. Symptoms and signs appear at about 12 hours of

age with respiratory distress.


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The Radiological findings include larger than

average lungs due to air trapping with apatchy rather coarse appearance due to

plugging of bronchi and distal consolidation.

There can be extensive radiological changes

without symptoms and vice versa.


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Hyaline Membrane Disease

Respiratory Distress

Syndrome


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Hyaline membrane disease (HMD) is a deficiency of

surfactant synthesized by type 2 pneumocytes,

which act to reduce the surface tension in the

alveoli, resulting in collapse of the alveoli and

increased effort required for respiration for their re-

expansion, alveoli are not formed until 26 weeks ofgestation.

Infants most at risk are those born prematurely, born

to diabetic mothers, second twins, infants born by

Caesarean section and suffering perinatal asphyxia.Hypoxia, acidosis, hypothermia and sepsis inhibit

surfactant activity.


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Diagnosis of HMD is a clinical diagnosis with the

infants presenting at 2-3hours of age with signs of

respiratory distress and grunting. If symptoms beginafter 8hrs they are not due to HMD. Symptoms may

increase in severity from 24-48 hrs, and gradual

improvement occurs after 48-72 days.

The typical radiological changes is a small volumechest, hazy shadowing, often described as ground

glass/reticulogranular pattern, and an air

bronchogram due to air in the bronchi contrasting

with fluid filled under-expanded alveoli. Changes aresymmetrical and bilateral.


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Congenital Diaphragmatic

Hernia


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New born presents with sever respiratory distress.

70%-90% are left sided and the majority are posterolateralthrough the foramen of Bochdalek.

An anterior hernia through the foramen of Morgagni presentslater. Hernias can be bilateral in bout 5%.

The ipsilateral lung will have a variable degree of hypoplasia.Compression of the contralateral lung in utero by the mass effectof the fluid filled hernia plus mediastinal shift may causecompromised growth of the lung.


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Bubbly appearance in the left hemithorax,

which is continuous with the abdomen

cavity (air-filled small bowel loops).

Mediastinal shift to the right side.

Non aerated left lung.


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Right sided hernia is much more difficult to diagnose

as bowel is a less prominent feature. Thepresentation may be delayed as the liver may

occlude the diaphragmatic defect. The mediastinum

is usually displaced to the left with a soft tissue

mass in the right lower chest due to herniation of theliver on x-ray.

Morgagni hernias show a centrally situated gas filled

structure overlying the heart and extending into both

sides of the chest, contrast study performed via anasogastric tube will confirm it. The main differential

diagnosis is a cystic adenomatoid malformation.


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Pulmonary Inflammatory

Disease


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Viral respiratory infections is a disease of the

airways, resulting in bronchitis, which

manifests as peribonchial cuffing, dirty hilum

and hyperinflation.

Bacterial pneumonia is a disease of the air

space, will manifest as focal lobarconsolidation with pleural effusion being

common.


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Foreign Body Inhalation


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Only large inhaled foreign bodies lodge in the

trachea, smaller objects lodge in the bronchial treeand affect the lower lobes or on the right, the middle

lobe. It may represent with pneumonia. Very small

foreign bodies, may migrate to the peripheral

bronchi, penetrate them and cause the formation of

a granuloma around them. Inorganic foreign bodies

are usually inert and their effects are due to

mechanical obstruction of the airway and to direct

injury to the bronchial wall. Organic matter, not only

causes mechanical problems but also localinflammation, which may cause stenosis.

85% of foreign bodies are non-opaque.


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Radiographic investigation include pairedinspiratory and expiratory films or, if easier,

brief fluoroscopy. Decubitus films are analternative mainly in young children, whereboth sides are taken. The lung with airtrapping will not compress in the dependent

position.O

ne lung or lobe may behyperlucent or hyperinflated, with air trappingon expiration, known as obstructiveemphysema, due to a ball valve obstruction,allowing entry of air during inspiration, but notallowing escape in expiration. Completebronchial obstruction can cause distalatelectasis.


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11 - paediatric chest imaging (1)

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