When your friend rings you from the hospital, boasting about his “collapsed lung” - you can quickly interrupt his pity parade and tell him that’s its actually a "pneumothorax". He’ll likely pivot the conversation in a bid to garner more sympathy. He’ll say that he has a tube sticking out of his chest resting in a bucket of water, bubbling away. At this point you can either tell him to stop being such a wuss…or send him a nice card - your choice. 
 
So, a collapsed lung that is "collapsed" but isn’t technically a collapsed lung…what? Let’s clear up the confusion.
 
A pneumothorax (‘pneumo’ - air, ‘thorax’ - chest) is a condition whereby air inappropriately enters the pleural space - the, usually empty, space between the lung and the chest wall. It’s important that the pleural space remains empty - by doing so, it creates a negative pressure/vacuum effect that allows the lung to expand fully on inspiration. 
 
When air enters this space, it causes a compression of the lung on that side. So yes, your friend was right, the lung has “collapsed” - but crucially, only secondary to a compressive force from outside the lung. 
 
In geeky, doctor language, a true lung collapse is when the lung fails to expand despite no external barrier getting in its way. There is no external compression from air or fluid in the pleural space. The most common cause of a significant lung collapse is a growing tumour invading the airway tract. The only real way to correct the collapse is to treat the internal cause. 
 
Refocusing ourselves on the pneumothorax, how does the air get into the pleural space? How did the FBI get into Hilary Clinton’s emails? - A leak. 
The leak can come from the lung itself, or from the chest wall. 
 
A leak via the chest wall is easy to understand. Someone gets in a car accident and a shard of glass pierces the skin and the muscle of the chest wall - air from the outside leaks in. Simple. 
 
A leak from within comes from a defect in the airway tract. Let’s imagine you have a small tear in a bronchiole - when you breathe in, some of that air will escape out into the pleural space via this internal leak.

How do you get a tear in the airway tract? 

A simple example would be someone who falls off their bicycle and lands on their side. The impact causes a small rupture in the tract. This would be labelled a traumatic pneumothorax.

Alternatively, sometimes the airway tract can just tear for no reason. This is most common in young, tall, skinny men. The upper part of their lungs struggle to stretch out as well as the rest of their body - leaving them quite strained. We call this type a spontaneous pneumothorax.
 
Symptoms of a pneumothorax include a sudden-onset shortness of breath and a sharp pain on one side - made worse when you breathe in (pleuritic). The level of pain or severity of breathlessness is dependent on the size and speed of the leak. 
 
In rarer circumstances, a pneumothorax can be life-threatening. The amount of air in the pleural space builds to the point whereby the heart, vessels, and windpipe are pushed to the other side of the chest. We call this type a tension pneumothorax. If there is a suspicion of a tension pneumothorax, a paramedic may decide to perform an urgent needle decompression to relieve some of the pressure. 
 
In the more routine case, you will come to the ED and have tests performed (including a chest x-ray which will make the diagnosis). If one lung can’t do all of the heavy lifting on its own, we can support you with oxygen. 
 
If the amount of air in the pleural space is minimal, and hardly compressing the lung - we will observe you for 24 hours, repeat an x-ray to ensure it’s stable and send you home. If the leak is resolved, the body will naturally resorb that air over time. You can follow up with your GP for a chest x-ray a week later and keep an eye out for any worsening symptoms. 
 
If the air is causing significant lung compression - the doctors will place a chest drain. It’s a procedure that can be done at the bedside with local anaesthetic. A clear tube will be inserted into your chest, in between the ribs. A stitch will often be applied to keep the tube in place. The other end of the tube will be placed into an underwater seal (essentially a fancy bucket with water in it). 
 
The difference in pressures will allow air to leave the pleural space, this is confirmed when we see bubbles coming from the end of the tube underwater. We’ll likely leave this drain in for one to three days and repeat chest x-rays to track the improvement. When the lung is fully re-expanded and you feel well, we’ll remove the drain and you can go home. 
 
After having had a pneumothorax, there are certain things you cannot do - to prevent recurrence. This includes scuba diving and space travel (due to the extreme changes in pressure). You also cannot fly for four weeks after the pneumothorax has resolved. These limitations are simply a rough guideline so please ask your own doctor for their opinion if you have big aero/astronautical plans!