Because the list of interstitial lung diseases is so extensive, encompassing more than 180 chronic lung diseases in which the interstitium is altered by inflammation and/or fibrosis, this chapter focuses on several inflammatory lung diseases of unknown etiology: usual interstitial pneumonitis, respiratory bronchiolitis, idiopathic bronchiolitis obliterans with organizing pneumonia, pulmonary Langerhans' cell granulomatosis, hypersensitivity pneumonitis, and lymphangioleiomyomatosis.
