major Tracheobronchial division

NORMAL  ANATOMY ON CHEST X-RAY

 The normal roentgen anatomy of the as seen on chest radiographs can be described in following headings.

Trachea

   Trachea is straight tube, midline in the upper part and deviates slightly to the right around the aortic knuckle. It shortens and deviates more to right on expiration. Its caliber is even with decreasing translucency as it is traced caudally. On plain chest radiograph the upper limits of coronal diameters in adults are 21 mm ( in females) and 25 mm (in males). The right tracheal margin ( Right paratracheal stripe ) can be traced down to the right main bronchus. It is 4 mm or less in thickness and measured above the azygos vein. The left paratracheal line is rarely visualized. After the age of 40 years, calcification of the cartilage rings of the trachea is a common finding. The enlarged azygos vein, which lies in the angle between the right main bronchus and trachea, may be normally seen as a round opacity in the tracheobronchial angle in the supine chest film.

Tracheobronchial Division

   The trachea divides into right and left main bronchus usually at D5 or D6 level in adults. The left main bronchus is longer and has more acute angle with trachea as compared to right main bronchus.

     The right main bronchus divides into upper lobe bronchus and bronchus intermedius. The upper lobe bronchus divides into apical, posterior and anterior segment bronchi. The bronchus intermedius divides into middle and lower lobe bronchi. Middle lobe bronchus has medial and lateral branches. The lower lobe bronchus has five branches; each for superior, anterior, lateral, posterior and medial basal segments of lower lobe. Absence of middle lobe on left side modifies the bronchial division on left side. The left main bronchus divides into upper and lower lobe bronchi. The upper lobe bronchus has two divisions; the upper division divides into apico-posterior and anterior branches to supply upper lobe, The lower division supplies the lingula with superior and inferior branches. The lower lobe bronchus on left side divides similar to the right side except the absence of separate medial basal branch. Major tracheobronchial divisions 

                              major Tracheobronchial division

Diagrammatic representation major tracheobronchial division as seen on frontal (A) and lateral (B) Orientation: (1-apical, 2-posterior and 3-anterior segments of upper lobe; 4-lateral segment of middle lobe/superior lingula, 5-medial segment of middle lobe/inferior lingula, 6-superior, 7-medial basal, 8-anterior basal, 9-lateral basal and 10- posterior basal segments of lower lobe)