The left upper lobe does not collapse in the same manner as the right upper lobe. This is a legacy of anatomy. There is no middle lobe on the left- the equivalent of the RML on the left is the lingula segment of the LUL.

1.Collapse and consolation can occur independently or together

2.Collapse can be partial or complete

3.It is often not clear to what extent the appearance is due to collapse or consolidation or both. The degrees of each are often unclear.

4.If a lobe is only partially collapsed and there is no accompanying consolidation, there may be no increase in opacity

5.In cases of pure collapse, only when the collapse is virtually complete will there be a significant increase in density of the affected lung

adapted from By Fred W. Wright Radiology of the Chest and Related Conditions: Together with an Extensive Illustrative Collection of Radiographs CRC Press, 2002

On the left there is no middle lobe; the anatomical equivalent region corresponding to the right middle lobe is known as the lingula, and like the RML, is also composed of two segments. Unlike their counterparts on the right however, the segments are stacked one on top of another, rather than side. http://lib.cpums.edu.cn/jiepou/tupu/atlas/www.vh.org/adult/provider/radiology/LungAnatomy/RightLung/RtLungSegAnat.html. Note that upper lobe pathology could appear very low on a chest X-ray image. The upper lobe is the anterior lobe as much as it is the upper lobe.

adapted from By Fred W. Wright Radiology of the Chest and Related Conditions: Together with an Extensive Illustrative Collection of Radiographs CRC Press, 2002

More information on lung anatomy here

• The PA view will show an area of increased opacity in the left upper lobe with an ill-defined margin.
  
• The increased opacity can be very subtle and may be most evident medially.
  
• Unlike RUL collapse, there is no sharply defined border- the abnormal increase in lung density merges into the normal lung below.
  
• The incease in lung density can be almost imperceptible on the PA view. The aortic knob is often obliterated.
  
• Similarly, the upper left cardiac shadow can be obliterated.
• The left hilum may be elevated
• There may be a lucent stripe between the medial edge of the collpased segment and the aortic arch. The is lower lube that has been pulled up by the collpased lung (Luftsichel Sign)
  

The PA view will show an area of increased opacity in the left upper lobe with an ill-defined margin. The increased opacity can be very subtle and may be most evident medially. Unlike RUL collapse, there is no sharply defined border- the abnormal increase in lung density merges into the normal lung below. The incease in lung density can be almost imperceptible on the PA view. The aortic knob is often obliterated. Similarly, the upper left cardiac shadow can be obliterated. The left hilum may be elevated

The PA view will shows an area of increased opacity in the left upper lobe with an ill-defined margin. Note the loss of the heart shadow/mediastinum and the mediastinal shift ? The left hemidiaphragm is elevated. decrease in LLL lung markings ? Luftsichel Sign

The lateral view is usually definitive and often highly characteristic. As the LUL collapses, the fissure moves forward pivoting at its lowest point Note that a similar appearance can be seen in congenital absence of a lobe

The lateral view demonstrates the highly characteristic collapsed lobe which now lies parallel to the sternum The collapsed lobe follows the anterior chest wall to the diaphragm

	This patients history is unknown. There is abnormal opacity demonstrated in the left upper chest. There is loss of visualistion of the upper mediastinum on the left There is evidence of compensatory emphysema on the left There is evidence of narrowing of the trachea from extrinsic compression on the left Appearances are suggestive of a LUL collapse associated with a tumour Luftsichel Sign Note- this appearance is the same as 'S' sign of Golden (LUL instead of RUL)
	There is evidence of LUL collapse.
	CT chest demonstrated obstruction of the LUL from a tumour.