Fig. 4.42 CT showing honeycomb lucencies in upper lobes (anteriorly and peripherally) bilaterally (stacked lucencies with bordering interstitial lines)

Radiological Signs

Interstitial markings can manifest in three basic forms on the CXR, and each form has its own differential diagnosis.

Linear form (lines): Reticulations (lines in all directions, not just the branching vessels) and septal lines (Kerley lines).

Nodular form (dots): Small, sharp, numerous, evenly distributed, uniform (especially uniform in shape) nodules.

Destructive form (holes): Peripheral, irregular cyst formation.

Linear Form: Lines

Linear Interstitial diseases include the following processes (pathologic types of the linear form).

L – Lymphangitic spread/metastases

I – Inflammation, Infection

F – Fibrosis

E – Edema

You can use LIFE-lines (like the lines around a boat) as a mnemonic to help you remember this list.

Case 4.14

Figures 4.43 and 4.44 show a CXR of a patient with lymphangitic spread, showing lines running in all directions, followed by a CT used as an example of septal lines.