The Idiopathic Interstitial Pneumonias. An Update and Review.

Idiopathic interstitial pneumonias (IIPs) are a group of disorders with distinct histologic and radiologic appearances and no identifiable cause. The IIPs comprise 8 currently recognized entities. Each of these entities demonstrates a prototypical imaging and histologic pattern, although in practice the imaging patterns may overlap, and some interstitial pneumonias are not classifiable. To be considered an IIP, the disease must be idiopathic; however, each pattern may be secondary to a recognizable cause, most notably collagen vascular disease, hypersensitivity pneumonitis, or drug reactions. The diagnosis of IIP requires the correlation of clinical, imaging, and pathologic features.