Tracheal bifurcation angle
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The tracheal bifurcation angle can have a wide range of normal values in patients and can vary significantly in serial radiographs. It is of poor diagnostic value due to the lack of sensitivity and specificity in identifying the underlying pathology.
The interbronchial angle is the angle between the central axis of right and left main stem bronchi 1. The subcarinal angle is the angle of divergence between the right and left main stem bronchi measured along their inferior borders 1.
The angle of tracheal bifurcation is not related to age and gender, however, there is a weak correlation with the shape of the chest 1.
The angle of tracheal bifurcation may be widened in the following conditions due to the mechanical splaying of the bronchi 1,2:
enlarged subcarinal lymph nodes
The mean angle of tracheal bifurcation is 60° (+/- 10° ), i.e. 95% of the patients have normal values between 40-80 °. The angle decreases by 10° on expiration. Also, the angle varies, sometimes by 20%, in serial radiographs. Thus, the wide range of normal values is a potential source of misinterpretation 1-3.
While an angle of tracheal bifurcation greater than 100° may predict left atrial enlargement, this is an insensitive and non-specific sign 4,5.
Thus absolute measurements of the angle of tracheal bifurcation (IBA/SCA) are of little diagnostic value and even grossly widened angles should not be interpreted as abnormal 1.
the tracheal bifurcation angle may be measured either as the interbronchial angle or the subcarinal angle
not related to age or gender
can have a wide range of normal values and its absolute measurement is of little diagnostic value
widening of the tracheal bifurcation angle is an insensitive and non-specific sign which must be interpreted in correlation with the clinical presentation
- 1. Haskin PH, Goodman LR. Normal tracheal bifurcation angle: a reassessment. (1982) AJR. American journal of roentgenology. 139 (5): 879-82. doi:10.2214/ajr.139.5.879 - Pubmed
- 2. Chen JT, Putman CE, Hedlund LW, Dahmash NS, Roberts L. Widening of the subcarinal angle by pericardial effusion. (1982) AJR. American journal of roentgenology. 139 (5): 883-7. doi:10.2214/ajr.139.5.883 - Pubmed
- 3. Alavi SM, Keats TE, O’Brian WM. The angle of tracheal bifurcation: its normal mensuration. (1970) AJR. American journal of roentgenology. 108 (3): 546-49. doi:10.2214/ajr.108.3.546
- 5. Murray JG, Brown AL, Anagnostou EA, Senior R. Widening of the tracheal bifurcation on chest radiographs: value as a sign of left atrial enlargement. (1995) AJR. American journal of roentgenology. 164 (5): 1089-92. doi:10.2214/ajr.164.5.7717208 - Pubmed
- 4. Taskin V, Bates MC, Chillag SA. Tracheal carinal angle and left atrial size. (1991) Archives of internal medicine. 151 (2): 307-8. Pubmed