Tri-lobed left lung

A female cadaver in the routine dissection hours of Ist MBBS Students revealed a trilobed left lung


ZOOM IN. PERICARDIUM RT LUNG LEFT LUNG DIAPHRAGM ALSO SEEN

The  Thoracic viscera insitu (right lung, pericardium with heart , left lung ) after the removal of anterior thoracic wall .Image shows the placement of forceps in the horizantal fissures bilaterally .

Lt Lateral view showing 3 lobes of left lung in situ.

 Diaphragm also seen

A pair of forceps is placed both in the horizontal and oblique fissures are seen. Cardiac notch of lung also seen.

Tri lobed left lung with oblique and horizontal fissure dissected out showing oblique and horizotal fissures

Anterior border of trilobed left lung showing the cardiac notch and lingula

TRILOBED LEFT LUNG DUE TO AN ACCESSORY HORIZONTAL FISSURE

During the dissection, a female cadaver displayed the left lung with two fissures just as the right lung.

Both the right and left lung were having the horizontal and oblique fissures at the same level.  The horizontal fissures of the left lung divided the entire lung parenchyma of the upper lobe into two lobes.   it was prominently seen on both costal and mediastinal surfaces.   During the development as the lung grows, the fissures that seprate budding individual bronco pulmonary segments get obliterated except along two planes which in fully formed lungs persists as horizontal and oblique fissures.  The accessory fissure could be the result of non-obliteration of spaces which normally do obliterate.   The accessory fissure may be of varying depth occurring between two broncho pulmonary segments.   In the present case it was deep.  Radiologically an accessory fissure can be mistaken for a lung lesion.   Most of the times the accessory fissures act as a barrier to the spread of infection creating as a sharply marginated pneumonia which could be wrongly interpreted as consolidation / atelectasis. Thus challenging the radiologists expertise. 

Note: 

1.       usually the left lung has only one deep oblique fissure, spiral in its course dividing it into two lobes.  And upper (superior) lobe forming the apex and the anterior margin of  the lung and the lower (inferior ) lobe forming the diaphragmatic major part of the posterior surface.

2.       The presence of oblique fissure in a normal scenario enables the uniform the expansion both the upper and lower lobes of the left lung.

3.       The fissures act as a reliable land mark in specifying thoracic and particularly pulmonary lesions