Understanding the Lung Interstitium
| Aspect | Description |
|---|---|
| Definition | The interstitium of the lung refers to the supporting connective tissue framework that lies between alveoli, airways, and blood vessels. It includes lymphatics, capillaries, fibroblasts, collagen, elastin fibers, and extracellular matrix. It provides structural support and facilitates immune surveillance, fluid balance, and gas exchange. |
| Histologic Components | Divided into: – Axial interstitium: surrounds bronchi and pulmonary arteries – Parenchymal (acinar) interstitium: delicate framework between alveolar walls – Peripheral (subpleural) interstitium: beneath pleura and interlobular septa Includes fibroblasts, reticulin, collagen, and sparse mononuclear cells. |
| CXR Appearance (Normal) | Not directly visible in healthy lungs. Interstitial structures (e.g., septa, interlobular lines) are below the resolution of plain radiographs. |
| CXR Appearance (Abnormal) | Becomes apparent when thickened, due to edema, fibrosis, inflammation, or tumor infiltration. Common signs include: – Reticular patterns (e.g., kerley lines) – Nodular patterns – Reticulonodular changes |
| CT Appearance (Normal) | Normal interstitium is microscopic and not well seen. Only interlobular septa and bronchovascular bundles may be faintly visible. |
| CT Appearance (Abnormal) | Becomes prominent with disease, seen as: – Thickened interlobular septa (smooth, nodular, or irregular) – Peribronchovascular thickening – Intralobular lines – Subpleural lines – Can produce reticular, nodular, ground-glass, or crazy paving patterns depending on cause. |
| Common Diseases Involving Interstitium | – Pulmonary edema (smooth septal thickening) – Idiopathic pulmonary fibrosis (IPF) (reticular, honeycombing) – NSIP (ground-glass + reticulation) – Lymphangitic carcinomatosis (nodular septal thickening) – Sarcoidosis (nodular thickening along bronchovascular bundles) |