Liver angulometry: a simple method to estimate liver volume and ratios

Abstract

Objectives: Volumetry is standard method for evaluating the volumes of the right liver (RL), left liver (LL), left lateral segments (LLS), total liver (TL) and future liver remnant (FLR). The aim of this study was to report a simple technique based on measurements of liver angles (angulometry) that can be used to predict liver ratios.

Methods: Fifty computed tomography (CT) scans obtained in subjects with normal liver were studied. Four CT scan levels were preselected: level 1 passed by the upper part of the hepatic veins; level 2 passed by the left portal vein branch division; level 3 passed by the right portal vein branch division, and level 4 passed by the gallbladder bed. Left and right tangent lines passing the liver edges were drawn and joined to the centre of the vertebra defining the TL angle. Two lines through, respectively, the plane of the middle hepatic vein and the left portal branches determined the angles of the RL, LL and LLS. Volumetric and angulometric data obtained on levels 2 and 3 in 50 different subjects were compared.

Results: Level 2 CT scans represented the most accurate way of obtaining angulometric measurements. The mean ± standard deviation (SD) angles of the TL and LL were 134 ± 12 ° and 55 ± 12 °, respectively. The mean ± SD percentages of the TL represented by the LL in angulometry and volumetry were 38 ± 7% and 36 ± 6%, respectively (non-significant difference). The mean ± SD percentages of the TL represented by the LLS in angulometry and volumetry were 25 ± 4% and 20 ± 3%, respectively (P < 0.05). The mean ± SD overestimation of the percentage of the TL represented by the LLS in angulometry was 2.7 ± 7.0%.

Conclusions: Angulometry is a simple and accurate technique that can be used to estimate the ratio of the FLR to TL volume on one or two CT (or magnetic resonance imaging) slices. It can be helpful for clinicians, especially before right or extended right hepatectomy and after right portal vein occlusion techniques.

Figure 1

Four levels of angulometry. Level 1 corresponds to the upper part of the liver on the plane of Couinard segments II, IV and VIII, where the three hepatic veins are visible inside the liver parenchyma. Level 2 corresponds to the plane of the left branch of the portal vein. Level 3 corresponds to the plane of the right portal vein and sectorial branches. Level 4 corresponds to the lower level of the plane of the gallbladder. C, central point on the vertebral body; M, middle line

Figure 2

The angle of the left lateral segment (LLS) corresponds to the angle delimited by a line passing by the central part of the left portal branches close to Couinard segments II, III and IV on level 2 (L2) and by the round ligament on level 3 (L3)

Figure 3

Morphometric data showed that 35% of patients had ‘L> R predominant liver’ meaning that the left liver had a > 40 ° development to the left liver edge on level 1 (L1), and 29% of patients had a ‘deep liver’, with a right liver angle of > 10 ° developed posteriorly from a horizontal line passing point C on level 4 (L4)

Figure 4

On level 2, mean ± standard deviation (SD) left liver : total liver ratios obtained in angulometry and volumetry, respectively, were 38 ± 7% (range: 18–54%) and 36 ± 6% (range: 15–52%), respectively (P = not significant). Mean ± SD left lateral segments : total liver (LLS : TL) ratios obtained in angulometry and volumetry differed significantly at 25 ± 4% (range: 20–31%) and 20 ± 3% (range: 13–25%), respectively (P < 0.05). The mean ± SD percentage of angulometric overestimation of the LLS : TL ratio was 2.7 ± 7.0%

Figure 5

This patient initially presented with multiple bilobar colorectal liver metastases (type III) that became resectable after 12 cycles of chemotherapy (5-fluorouracil, oxaliplatin and irinotecan). The hypertrophy progression rates after the laparoscopic first step, including radiofrequency ablation (RFA) of the left lateral segment (LLS) nodules, plus right portal vein ligation (PVL) showed significant changes in LLS : total liver (LLS : TL) ratios measured on levels 2 and 3 (L2 and L3). After right PVL, LLS angles progressed from 46° to 68° on L2 and from 43° to 68° on L3. The progression LLS: TL angulometric ratios were from 38% to 46% and from 34% to 45% on L2 and L3 respectively