Q. Can you please tell me about spontaneous pneumothorax? We were pretty frightened when this happened to our son. First was the fact that out of the blue his lung collapsed. Then he had to have a tube sticking out of his chest until it healed. What causes this problem? Will he keep getting it?

A. A pneumothorax, the presence of air between the chest wall and the lung cavity, can be frightening, but with prompt treatment, full recovery is the rule.

A pneumothorax occurs when a lung collapses. There are two kinds: primary and secondary. The primary type occurs in the absence of any obvious lung disease. The secondary type stems from an underlying lung disease, such as emphysema.

I'll assume your son had primary pneumothorax. This typically occurs in young men between the ages of 20 and 40 who smoke. Although the lung collapse seems to occur for no reason, it stems from the bursting of a small weak spot on the surface of the lung. This weak spot, known as a bleb, is like a little bubble that has the potential to pop. When it does, air escapes into the chest cavity and the lung partially collapses.

In most cases, a spontaneous pneumothorax is very painful. It causes sharp, stabbing chest pain and makes breathing painful. It often causes shortness of breath and a sudden cough as well. A chest X-ray will usually reveal the collapsed lung, making diagnosis easy. In a few cases, the collapse can be small enough that it is difficult to see on an X-ray. Repeating the procedure may reveal it.

If the collapse is small, you may not need any treatment. Over the course of a week or two, the escaped air will gradually resorb. Your lung will heal and expand back to normal.

If the collapse is larger, you'll need to have the escaped air removed. This will allow your lung to expand and will help speed healing. There are several ways of removing the air. The simplest is by inserting a needle into the chest cavity and drawing out the extra air.

Other options are inserting a small catheter or a larger tube into the chest to remove the air. These tubes will stay in place until the expanded lung has a chance to heal, which usually takes a few days.

Once you've had a primary pneumothorax, you can get it again. It can even recur on the opposite side. If you get two or more, you can have a procedure to try to prevent a recurrence.

One option for surgery is instilling a chemical in the chest cavity that makes the lung adhere to the inner chest wall. Then the lung won't collapse if a small bleb bursts. Another option is to have any visible blebs removed.

Secondary pneumothorax occurs in people with an underlying lung disease, such as emphysema. These cases can be more serious, because with a lung already damaged by disease, a collapse could be fatal.

In these cases, doctors usually insert a chest tube to remove the extra air. Simply removing the air through a needle generally isn't enough. Doctors will also be more likely to instill a chemical to make the lungs adhere to the chest wall right away rather than wait for a recurrence.

In either type of pneumothorax, people can develop a life-threatening complication known as tension pneumothorax. "Tension" refers to the air pressure within the chest cavity. In this situation, air continues to leak out of the lung into the chest, further collapsing the lung. It also starts pushing the heart toward the opposite side of the chest. The combination of increased air pressure and pushing the heart to the side impairs blood flow throughout the body. If the tension is not quickly relieved, this process can be fatal.

A tension pneumothorax can also occur in people who are on respirators in the hospital. This complication can also affect infants on respirators, because their lungs may not be strong enough to withstand the pressures of artificial ventilation.

Finally, a pneumothorax can occur during trauma, such as from a knife or bullet wound. It can also occur from blunt trauma, with the force of impact causing the lung to collapse. And a broken rib can puncture the lung, causing it to collapse and form a pneumothorax. In these cases, a chest tube is inserted until the lung has a chance to heal.

Jay Siwek, chairman of the department of family medicine at Georgetown University Medical Center, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.

Consultation is a health education column and is not a substitute for medical advice from your physician. Send questions to Consultation, Health Section, The Washington Post, 1150 15th St. NW, Washington, DC 20071. Questions cannot be answered personally.