There are many causes of interlobular septal thickening, and this should be distinguished from intralobular septal thickening. Thickening of the interlobular septa can be smooth, nodular or irregular, with many entities able to cause more than one pattern.
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Pathology
Causes of septal thickening include
Smooth
- pulmonary edema
- lymphangitic carcinomatosis
- lymphocytic interstitial pneumonia (LIP): often ground glass opacities are also present
- pulmonary hemorrhage: usually ground glass opacities are also present
- acute lung rejection
- lymphoma
- leukemia: pulmonary manifestations of leukemia
- Churg-Strauss syndrome
- Niemann-Pick disease
- congenital lymphangiectasia
- amyloidosis: only sometimes visible
- non-specific interstitial pneumonia (NSIP): usually ground glass opacities are also present
- bronchiectasis 2
- Erdheim-Chester disease
- yellow nail syndrome
- diffuse pulmonary lymphangiomatosis
Nodular
- lymphangitic carcinomatosis
- Kaposi sarcoma
- lymphoproliferative disorders
- sarcoidosis 5
- Niemann-Pick disease
- amyloidosis: only sometimes visible
- silicosis
- coal worker's pneumoconiosis (CWP)
Irregular
- sarcoidosis
- idiopathic pulmonary fibrosis: UIP, etc. interlobular septal thickening predominant finding
- asbestosis
- upper lobe predominance: pleuroparenchymal fibroelastosis (though a very rare entity) 4
Radiographic features
Plain radiograph
- Kerley A lines: long (2-6 cm) lines oriented towards the hila
- Kerley B lines: short ~2 cm line oriented perpendicular to the pleura
