Nonspecific interstitial pneumonia: radiologic, clinical, and pathologic considerations.

Nonspecific interstitial pneumonia (NSIP) has variable clinical, pathologic, and radiologic manifestations. Cellular and fibrotic NSIP are the two main histologic subtypes and differ from one another in the degree of inflammation and fibrosis. It is important to differentiate NSIP from other diffuse lung diseases, especially usual interstitial pneumonia and hypersensitivity pneumonitis, owing to differences in prognosis and treatment. At high-resolution computed tomography, the most common findings suggestive of NSIP are lower lobe peripherally predominant ground-glass opacity with reticular abnormality, traction bronchiectasis, and lower lobe volume loss. Nodules, cysts, and areas of low attenuation are uncommon and should point one toward other diagnoses. Because many cases of NSIP are associated with collagen vascular diseases, it is important to look for associated findings that may suggest an underlying collagen vascular disease. Given the difficulty clinicians, pathologists, and radiologists experience in making the diagnosis of NSIP, a group approach in which these specialists work together to reach a consensus diagnosis has the highest likelihood of achieving the correct diagnosis.