Diseases affecting the peribronchovascular interstitium: CT findings and pathologic correlation

Central bronchi and pulmonary arteries are surrounded and enveloped by a strong connective-tissue sheath termed the peribronchovascular interstitium, extending from the level of the pulmonary hila into the peripheral lung. Thickening of the peribronchovascular interstitium can be seen in a wide variety of diseases. The CT appearance can be smooth, nodular, or irregular depending on the underlying cause. Many of the diseases affecting the peribronchovascular interstitium are entities that show a predilection for lymphatic routes, such as sarcoidosis, pulmonary lymphangitic carcinomatosis, silicosis, and lymphoproliferative disorders. There are other entities that mainly affect the peribronchovascular interstitium without a predominant perilymphatic distribution, such as hydrostatic pulmonary edema, cryptogenic organizing pneumonia, Kaposi's sarcoma, interstitial pulmonary emphysema, and interstitial hemorrhage. Although there is an overlap in radiologic features, some CT findings are useful in differentiating among these entities. When CT shows mainly peribronchovascular abnormality, the differential diagnosis is considerably reduced, and it is generally possible to reach the correct diagnosis by considering the clinical context. We illustrate the CT findings and pathologic correlation for a number of different disorders that mainly affect the peribronchovascular interstitium.