Pneumothorax, the air in the pleural space, can be evident or discreet, thus easily missed. Whether traumatic or spontaneous it's always important to rule it out and it's best having it in your general search algorithm.

Fig 1: Recurrent spontaneous pneumothorax in a 14-year-old patient (1st time)....

"You can only see what you look for..."

   What to look for?

• visceral pleura - a thin, defined white line with no lung markings peripheral to it
• the line parallels the chest wall contour - it's curved at the lung apex
• space between the visceral pleura and parietal pleura appears more lucent compared to the surrounding lung
• pneumomediastinum and subcutaneous emphysema may accompany it

Fig 8: Patient from Fig 1, CT was done during the workup. Areas of incipient...

   Where to look for? 

• air rises to the highest point of the pleural space
• erect chest X-ray - lung apex is where subtle pneumothorax is easily overlooked - double check it.
• supine chest X-ray - in supine position highest point of pleural space is anteriorly - search the lung base
• deep sulcus sign - air collected in the lateral costophrenic sulcus on supine x-ray, appears more lucent and deeper than the unaffected side
• in supine position air may also accumulate medially, against the heart - left heart border is sharply black  outlined by lucent air compared with the contralateral side

Fig 2: Deep sulcus sign left, supine x-ray. Neonate hospitalized on 1st day of life...

Fig 3: Patient from Fig 2, CT was done and bilateral pneumothorax was confirmed. In...

An unusual rare case of congenital bilateral pneumothoraces (also known as buffalo pneumothorax or buffalo chest), caused by abnormal anatomic pleuropleural communication. Buffalo chest's most common aetiology is iatrogenic.

Fig 4: Patient from Fig 2 - 3, coronal plane - left-sided pneumothorax correlates with...

  Mimicks

• extrapulmonary: skin folds (one of the most common mimics), superior scapular margin, hair, venous catheters, clothes etc.)
• intrapulmonary: apical blebs, large bullae
• lung vessel markings peripheral to the suspected white line should help discover the imposter

Fig 5: Left-sided pneumothorax in a newborn with RDS. X-ray was done on the 2nd day of...

 When in doubt - tips and tricks

• complete expiration erect X-ray - pneumothorax is easier to spot because the lung is denser
• lateral decubital view - suspected side up, air will rise to it

   If not helpful, next modality to ensure the diagnosis is CT.

Pneumomediastinum, extraluminal air within the mediastinum, is an uncommon condition in a pediatric population, even more so a spontaneous one.

To recognize it, know the signs:

• presence of subcutaneous emphysema in soft tissues and/or lucent lines of gas in the neck
• continuous diaphragm sign - outlined central part of the diaphragm by air which is normally in continuum with heart silhouette
• ring around the artery sign - air outlines the pulmonary artery or its branches
• tubular artery sign - air outlines aortic branches
• angel wing sign (a.k.a. spinnaker sign) - thymic lobes are outlined by air and displaced laterally forming the "angel wings" (or spinnaker sails), specific for the pediatric population

Fig 6: A 10-year-old patient was hospitalized due to asthmatic exacerbation caused by...

Fig 7: Patient from Fig 6, follow-up. On the left, 1st follow-up X-ray was done 2 days...

Fig 9: Pneumomediastinum along the left cardiac contour in a 16-year-old patient...

Fig 10: A 12-year-old patient presented with worsening ongoing chest pain for several...

Fig 11: Patient from Fig 10, CT shows pneumomediastinum in every mediastinal...

Fig 12: Spontaneous pneumomediastinum with extensive subcutaneous emphysema in a...

Congenital lobar overinflation (previously called congenital lobar emphysema) is a rare congenital condition and a true diagnostic gem to recognize. 

• one or more affected lobes progressively hyperinflate causing respiratory distress 
• clinical signs usually evident until 6-months-old, more common in boys
• unknown cause in most cases
• more common in the upper (left>right) and middle lobe, rare in the lower lobes

   Features on X-ray:

• hyperlucent and distended lobe (usually upper)
• surrounding lobes are compressed
• contralateral mediastinal shift is possible in extreme cases

Fig 13: Congenital lobar overinflation in 2-month-old infant, dyspnoea workup....

Fig 14: Congenital lobar overinflation, the patient from fig 13. Hyperinflation of the...

More than one pathology.. Or how not to have a "happy eye"

Fig 15: A 3-year-old patient presented with fever, cough and poor general condition, at...

Fig 16: Patient from Fig 15, follow-up X-ray immediately after the punction and...

Fig 17: An 8-month-old presented with bronchial obstruction, fever and no response to...

Fig 18: A 16-year-old patient, polytrauma caused by a motorcycle accident, supine...

Fig 19: Patient from Fig 18. Confirmed traumatic left-sided hemopneumothorax with...

Fig 20: Patient from Fig 19, follow-up after 7 days, regression of contusion,...

Pneumatocoele is a cystic space in the lung containing air.

• age of presentation, size, as well as appearance, varies
• usually a result of pneumonia, trauma or after positive pressure ventilator therapy 
• post-traumatic - if lung tear communicates with a bronchus
• mature pneumatocoele should have thin, regular walls containing air with no/very little fluid
• immature pneumatocoele appearance varies depending its cause

Fig 21: Patient from Fig. 18-20, 10 days after discharge from the ICU came back with a...

Fig 22: Patient from Fig 19-21, the diagnosis was confirmed on CT - lung abscess

Fig 23: An 11-year-old patient presented with a high fever and a cough. X-ray showed...

Fig 24: Patient from Fig 23, an X-ray was done after pleural punction. A collapsed lung...

The importance of an air-fluid level - patients with pleural effusion and no lateral meniscus to it,  seemingly fully expanded lung - can be an only sign of a small pneumothorax (especially postprocedural punction/biopsy etc.)

Fig 25: Patient from Fig 23-24, follow-up X-ray showed reexpansion of the left lung...

Fig 26: Patient from Fig 23-26, 2nd follow-up X-ray showed progression of pneumonia and...