An interstitial pattern refers to changes in the lung’s interstitial tissue, the supportive tissue surrounding the alveoli, airways, and blood vessels. This pattern is characterized by thickening or inflammation of the interstitial space.
Etymology:
“Interstitial” comes from the Latin “interstitium,” meaning “space between,” and refers to the tissue between the alveoli and vasculature in the lungs.
How does it appear on each relevant imaging modality:
Chest X-ray:
Parts: Increased reticular or linear opacities, representing interstitial thickening.
Size: Can involve small or large areas, often seen in both lungs.
Shape: Fine, network-like lines (reticular), sometimes nodular or diffuse.
Position: Often bilateral, but can have zonal predominance (e.g., more prominent in upper or lower lobes). ILD subtypes such as UIP (Usual Interstitial Pneumonia) and NSIP (Non-specific Interstitial Pneumonia) are typically predominant in the lower lobes.
Character: Ground-glass opacities or fine lines; in advanced cases, fibrosis or honeycombing.
CT Chest (High-Resolution CT – HRCT):
Parts: Widespread thickening of interlobular septa and peribronchovascular markings.
Size: Can be diffuse or patchy.
Shape: Reticular or nodular patterns, with honeycombing in advanced cases.
Position: Bilateral involvement, with potential upper or lower lobe dominance. UIP and NSIP also show lower lobe predominance.
Character: Clear delineation of fibrosis, cystic spaces, or ground-glass opacities.
Ultrasound:
Parts: Typically not used for diagnosing interstitial patterns but may show pleural thickening in severe cases.
Size: May correlate with effusion or consolidation, seen in severe interstitial lung disease (ILD).
Differential diagnosis:
Infection: Viral pneumonia, tuberculosis, or bacterial pneumonia.
