Pulmonary Edema - Interstitial

Pathophysiology:  Due to alveolar capillary leakage of electrolytes and water and in some cases, of larger molecules into the inter-alveolar walls, interlobular septae, and into the peri-bronchial and peri-vascular sheaths.  The commonest cause is heart failure. Other causes include hypervolemia, hypoproteinemic states, acute or chronic renal failure, and any of the multiple causes of Adult Respiratory Distress Syndrome (ARDS)

Clinical Clues:

1.      The CXR is more sensitive than the best clinician in detecting interstitial edema.

2.      Clear cut interstitial edema is often not seen in ARDS.  There is fibrinogen and fibrin trapping the free flow of water and the florid airspace edema masks the interstitial findings.

CXR Findings:

1.      thickened visible interlobular septae (Kerley B and Kerley A lines)

−        Kerley B lines: parallel lines running along the outer chest wall, like steps in a ladder

−        Kerley A lines: curvilinear lines starting close to the hila and extending peripherally

2.      Central peribronchial cuffing

3.      Central perivascular fuzziness

4.      Often enlarged heart, evidence of cardiac or renal disease (ie. effusions, renal osteodystrophy)

“Aunt Sophies”: The cardinal sign of interstitial edema is Kerley B lines.  Any process which thickens interlobular septae will produce Kerley B lines.

1.      Fibrosis: many chronic interstitial lung diseases (eg. UIP)

2.      Chronic bouts of edema leading to fibrosis

3.      Tumor: lymphangitic carcinomatosis

4.      Infection: interstitial pneumonias

5.      COLD (chronic obstructive lung disease), with infection, fibrosis and septal fibrosis

6.      Rarely, infiltrative processes (eg. amyloidosis)