Most common interstitial abnormality identified on X ray

What is the most common interstitial abnormality identified on X ray?

Interstitial pulmonary edema, usually caused by congestive heart failure, is the most common interstitial abnormality encountered in daily practice. A diagnosis of interstitial pulmonary edema should be considered in all cases of interstitial abnormality detected on a chest radiograph. In many cases, it might be advisable to diurese the patient and repeat the chest radiograph as the first diagnostic test.