Septal lines, also known as Kerley lines, are seen when the interlobular septa in the pulmonary interstitium become prominent. This may be because of lymphatic engorgement or oedema of the connective tissues of the interlobular septa. They usually occur when pulmonary capillary wedge pressure reaches 20-25 mmHg.
Kerley A lines
These are 2-6 cm long oblique lines that are <1 mm thick and course towards the hila. They represent thickening of the interlobular septa that contain lymphatic connections between the perivenous and bronchoarterial lymphatics deep within the lung parenchyma. On chest radiographs they are seen to cross normal vascular markings and extend radially from the hilum to the upper lobes. HRCT is the best modality for the demonstration of Kerley A lines.
Kerley B lines
These are thin lines 1-2 cm in length in the periphery of the lung(s). They are perpendicular to the pleural surface and extend out to it. They represent thickened subpleural interlobular septa and are usually seen at the lung bases.
Kerley C lines
Kerley C lines are short lines which do not reach the pleura (i.e. not B or D lines) and do not course radially away from the hila (i.e. not A lines).
Kerley D lines
Kerley D lines are exactly the same as Kerley B lines, except that they are seen on lateral chest radiographs in the retrosternal air gap 2.
- pulmonary oedema
- interstitial pulmonary fibrosis
History and etymology
Kerley lines are named after Sir Peter James Kerley (1900-1979), an Irish radiologist who in addition to describing the interstitial lines now known as Kerley lines, also attended to King George VI 3,4.
- 1. Reed JC. Chest radiology, plain film patterns and differential diagnoses. Mosby Inc. (2003) ISBN:0323026176. Read it at Google Books - Find it at Amazon
- 2. Kirchner J. Chest Radiology: A Resident's Manual. Thieme Medical Pub. (2011) ISBN:3131538716. Read it at Google Books - Find it at Amazon
- 3. Sekar T, Swan KG, Vietrogoski RA. A beeline through Sir Peter James Kerley's life. AJR Am J Roentgenol. 2011;196 (4): W375-9. doi:10.2214/AJR.10.5825 - Pubmed citation
- 4. Obituary in British Medical Journal PDF