It is not uncommon to diagnose tension pneumothorax radio logically rather clinically as early signs of pneumothorax can be over looked.

I think, most of the tension pneumothoraces should be diagnosed clinically rather than radiographically

However, I agree with Richard that sometimes, this may be first apparent on imaging

In critically ill ICU patients the signs of tension pneumothorax can mimic other pathology but one should have a low threshold to obtain imaging studies for confirmation.

A really good review on this subject is at 

S Leigh-Smith, T Harris. Tension pneumothorax—time for a re-think? Emerg Med J 2005;22:1 8-16

This review questions the traditional teaching on this subject, and intelligently differentiates between patients who are spontaneously breathing, and those who are being ventilated. 

I hope this helps,

Jason

An initial STAT portable chest x-ray is best approach in a hospital setting, as clinical dx. can be deceiving.

Thanks Tibor

There is a big difference clinically between tension pneumothorax in spontaneous breathing patients and those on a ventilator - the latter usually developing much more rapidly. Once " tension"  has developed, however, they are the same and usually easy to diagnose clinically. A chest X-ray is of course desirable, but by definition a tension pneumothorax is an emergency and definitive action precludes prior investigation.

Peter