| Type | Location | Key Feature | |------|----------|--------------| | | Upper/mid zones, central | Long (2–6 cm), radiating from hila into lung, unbranched. Less common now due to better CT correlation—often represent thickened deep lymphatics. | | Kerley B lines | Peripheral, especially costophrenic angles | Short (1–2 cm), horizontal, reaching pleura at right angles. Most common and specific type. | | Kerley C lines | Lower zones, reticular pattern | Finer, reticular (net-like) opacities—actually represent overlapping B lines in a limited area. Now considered non-specific. |
With the advent of High-Resolution Computed Tomography (HRCT) in the 1980s and 90s, the visualization of septal lines underwent a revolution. HRCT allowed radiologists to see the lung anatomy with near-microscopic precision. On an HRCT scan, normal interlobular septa are often invisible or seen only as very faint, hair-thin lines. When they become visible, they appear as distinct linear opacities, usually 1 to 2 centimeters in length, often bordering a central dot that represents the pulmonary artery feeding the lobule. This "dot and line" appearance allows clinicians to map the secondary lobule with high precision, turning the interpretation of septal lines from guesswork into an exact science.
In the complex, spongy anatomy of the human lung, structure dictates function. While the primary purpose of the lung is the gas exchange that sustains life, this process relies on a meticulous architectural framework. Buried deep within the secondary lobules—the basic functional units of the lung—lie the septal lines. These are the thin, connective tissue divisions that separate one lobule from another. septal lines
Septal lines are a significant radiological feature that can be observed on chest X-rays and CT scans. Understanding the causes and clinical significance of septal lines can help clinicians diagnose and manage various pulmonary and cardiac conditions.
Originally described by Sir Peter Kerley in 1951. | Type | Location | Key Feature |
On high-resolution CT (HRCT), septal lines are seen as:
Septal lines are short, horizontal lines that are seen at the lung periphery, typically at the intersection of the interlobular septa and the pleura. They are caused by the thickening of the interlobular septa, which can occur due to various reasons such as: Most common and specific type
:
To understand the septal line, one must first understand the geography of the lung. The lung is not a uniform balloon but a collection of millions of tiny polyhedral structures called secondary pulmonary lobules. These lobules vary in size but generally measure between 1 and 2.5 centimeters in diameter. Each lobule contains a central bronchiole and a pulmonary artery branch, surrounded by a sleeve of functional lung tissue (alveoli).