Line or band like shadows

Line or band like shadows: all lines shadows within the lung are abnormal except fissures and walls of large central bronchi:
1- septal lines: the most important one.
Interlobular septa are connective tissue planes containing lymph vessels, are normally invisible, only greatly thickened septa can be seen on CXR.
Septal lines are much thinner than pulm. Blood vs.
On plain CXR septal lines see: Karely B lines horizontal lines, never more than 2 cm in length, best seen at periphery of lung, unlike blood vs. often reach edge of lung.
mild thickening of minor interlobular septa are readily identified by CT.
Two imp. Causes of thickened interlobular septa: pulm. Edema and lymphangitis carcinomatosa.
2- pleuropulmonary scars and linear(discoid) atelectasis: are common causes of line and band like shadows.
Linear scars are due to previous infection or infarction, usually reach the pl. and often associated with visible pl. thickening.
Linear(discoid) atelectasis: horizontally oriented bands or discs of collapse.
3- emphysematous bullae: bullae(blebs) : are air spaces devoid of blood vs., may be rounded and traversed by thin line shadows, have few if any normal vs. within them.
4- the pleural edge of pneumothorax: seen as line, approximately parallel with chest wall, no lung vs. seen beyond pl. line.