The caudate-right lobe ratio (C/RL) is used in the assessment of the liver, usually in the setting of cirrhosis, where there is atrophy of the right lobe with hypertrophy of the caudate lobe.
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Method
image level: axial slice immediately below the bifurcation of the main portal vein
line 1: parasagittal line drawn through the right lateral border of the main portal vein
line 2: parasagittal line drawn through the left lateral border of the caudate lobe
line 3: line orthogonal to lines 1 and 2 midway between the main portal vein and the inferior vena cava extended to the right liver edge
caudate measurement (C): along line 3, between lines 1 and 2
right lobe measurement (RL): along line 3, from right liver edge to line 1
caudate-right lobe ratio: C/RL
Interpretation
C/RL <0.6 = normal (does not exclude cirrhosis)
C/RL 0.6-0.65 = borderline
C/RL >0.65 = 96% likely to be cirrhotic
C/RL >0.73 = 99% likely to be cirrhotic
Modified measurement
An alternative placement of line 1 has been proposed by Awaya et al. as being more sensitive and specific 2. Rather than drawing line 1 through the right lateral border of the main portal vein, the line is drawn through the right lateral aspect of the right portal vein bifurcation. In this instance, a C/RL >1 is considered cirrhotic.