My problem is spontaneous pneumothorax which I suffered once 12 years ago without recurrence ever since. It happened during basketball practise and in the consequent x-ray examination it was discovered that my left lung had collapsed. No pleurodesis were performed. Now, according to the literature I've been reading, a history of pneumothorax is a strong contraindication of diving due to its high recurrence rate and its possibility to turn into tension pneumothorax which is described as a fatal condition.
Since I haven't had recurrence in 12 years I would like to know what kind of risk I am assuming by continuing diving. Also, I would like to know if there are any diving practises etc I should avoid /follow in order to reduce the risk involved. Finally, is there a way (x-rays, MRI etc) to determine the situation with my lungs?
In the literature pleurodesis is mentioned as a cure. What kind of operation is this?
Hopefully you can find time to answer these questions.

A primary spontaneous pneumothorax usually reflects underlying cystic lung conditions, and these should be investigated by means of X-ray, CAT Scan, MRI, pleuroscopic practices. The recurrence rate is 33-50%, but it tends to decrease with time. PSpontaneous pneumothorax is, as you correctly say, considered an important contraindication to scuba diving, due to the reasons that you report.
However, a relapse-free period of over 10 years, together with the increase of age, make the recurrence less and less likely with time. Also, the fact that your pneumothorax occurred during the practise of a strenuous physical activity, make it, so to speak, more "justified" and "less likely" to recur during normal life. In fact one should exclude that the condition did not occurred as a consequence of a "blunt" trauma while playing basketball.
Scuba diving, per se, is not an activity with an inherent high risk of causing a pneumothorax - unless in the case of a pulmonary barotrauma on the ascent - it is simply a matter of the wrong thing happening at the wrong time and in the wrong place, as the coincidence of a spontaneous pneumothorax occurring during a dive may have the disastrous effect that you mention and can also facilitate the possibility of a concomitant arterial gas embolization.
However, as I said above, this occurrence is more and more faible as time from the original episode elapses.
Some authors tend to think that a 5 year relapse-free interval is enough to resume diving, while others tend to consider spontaneous pneumothorax as permanently disqualifying.
Pleurodesis is a surgical intervention by which the pleural space is permanently obliterated, by irritation and subsequent scar-healing ( usually with sterile talcum powder) or by surgical removal of one of the pleural sheets. Alternative techniques, with endoscopic removal of peripheral lung cysts have also been used, in cases of known and well localized cystic formations.