You have to think about this using the concept of CONDITIONAL PROBABILITY. Another way to ask this type of question is like this: “I show you a patient with spontaneous pneumothorax. Which other thing is most likely to be true about that person?” Or you can phrase it these ways:

• Given a CONDITION (spontaneous pneumo), what other finding is most likely to be the case?
• Given a pool of people with spontaneous pneumothorax, what other thing is most likely to be true about them?

In other words, of all people who end up with spontaneous pneumo, the most common other thing about them is that they are MALE & THIN.

If I gave you a bucket of spontaneous pneumo patients -- and you reached your hand in there and pulled one out -- what scenario would be more common: In your hand you have a smoker or in your hand you have a thin male? It’s the latter.

If I gave you a bucket of spontaneous pneumo patients -- and you reached your hand in there and pulled one out -- what scenario would be more common: In your hand you have a smoker or in your hand you have a thin male? It’s the latter.

Why spontaneous? He's engaging in an active sport with an increased risk of Traumatic injury. So we really just assume hes not injured because the stem doesnt directly say he's injured? These questions lead to too many assumptions. (in my opinion)

Rupture of pulmonary blebs are a common cause of spontaneous pneumothorax in young adult males that are tall and thin. I know it's also associated with smoking, but gender and body habitus seemed like the more likely answer here since the patient is a young male.

Here's some epidemiology information about spontaneous pneumos: There are two kinds, primary spontaneous pneumos (PSP) and secondary (SSP). PSPs occur in people aged 20-30 years, with a peak incidence is in the early 20s, is rarely observed in people older than 40 years, with a male to female ratio of 6.2:1, and most frequently occurs in tall, thin men, though smoking increases risk even further. SSPs occur in patients with underlying lung conditions, such as COPD/older patients. If the patient's demographic was older and had history of lung disease, but that wasn't an option, then I think smoking would be the appropriate choice because smoking is the biggest risk factor for underlying lung conditions.

Regarding the trauma, traumatic injury pneumos most commonly occur due to motor vehicle acidents where there is injury (i.e. fracture) to chest wall, and with blast injuries. Although the question didn't specify the chest wall was void of fractures, it also didn't say fractures were present, so I think it would be safe to assume that the collision injury didn't have enough force to cause the pneumo, especially with keeping in mind the epidemilogy of primary spontaneous pneumos.

At least, this is my thought process having researched it more, now.

Patient has a hemithorax + CXR shows trachea deviates towards the hemithorax --> most likely diagnosis is spontaneous pneumothorax.

Epidemiologically, spontaneous pneumothorax is most associated with thin males

Everywhere I found (UpToDate and several papers) said the smoking is the biggest risk factor for spontaneous pneumothorax, with body habitus and gender being a lesser risk. Am I just completely misunderstanding the question?