Determining Future Liver Remnant (FLR) Volume and Safe Resection Thresholds

Imaging Technique and Volumetry Calculation

Contrast‑enhanced portal‑phase CT with dedicated volumetry software is used to calculate the future liver remnant as a percentage of total liver volume after subtracting tumor volume; minimum FLR thresholds are ≥ 20 % for normal livers, ≥ 30‑40 % for chronic liver disease with Child‑Pugh A cirrhosis, and up to 40 % for severe steatosis or cholestasis. [1][2]
Portal‑phase CT provides optimal parenchymal enhancement and clear delineation of hepatic structures, which is essential for accurate volumetric analysis. 3
Volumetry workflow: (1) subtract tumor volumes from total liver volume to obtain functional liver volume; (2) subtract the planned resection volume to derive FLR volume; (3) express FLR as FLR ÷ functional total liver volume × 100 %. [1][2]
The 2025 EASL guidelines state that CT volumetry is a reliable and readily available predictor of post‑hepatectomy remnant liver volume (strong consensus). 3
3‑D reconstruction software yields a better correlation with actual future liver volume than conventional 2‑D volumetry and is especially useful for planning complex resections. 3

An FLR ≥ 20 % of total liver volume is required for patients with healthy, non‑cirrhotic livers; post‑hepatectomy liver failure (PHLF) occurs in 30 % of cases when FLR ≥ 20 % versus 50 % when FLR < 20 %, and mortality rises from 3 % (FLR 20‑30 %) to 11 % (FLR ≤ 20 %). 1

For chronic liver disease, an FLR ≥ 30‑40 % is necessary.
- 30‑35 % is adequate for mild steatosis, cholestasis, or early Child‑Pugh A cirrhosis.
- 40 % is required for severe steatosis or cholestasis.
- Resection of up to 50 % of liver volume may be considered only in highly selected cirrhotic patients without functional impairment or portal hypertension. 1

Child‑Pugh B or C cirrhosis and clinically significant portal hypertension are absolute contraindications to major resections (> 2 segments); even limited resections can precipitate PHLF. The 2025 EASL guidelines provide a strong consensus on this recommendation. [5][1]

The right liver typically comprises ≈ 65 % of total liver volume but varies from 49 % to 82 %; the left liver accounts for ≈ 35 % (range 17‑49 %). This variability mandates patient‑specific volumetric assessment rather than reliance on fixed segment percentages. 1

When the calculated FLR falls below the recommended thresholds, pre‑operative portal vein embolization (PVE) should be performed to induce hypertrophy of the future remnant over 4‑8 weeks while the embolized portion undergoes atrophy. [4][2]

CT volumetry should be supplemented with functional tests when underlying parenchymal disease is uncertain:
- Pre‑operative biopsy of the FLR to predict PHLF risk. 1
- Indocyanine green (ICG‑R15) testing to evaluate hepatic functional reserve. 3
- ALBI grade, FIB‑4 score, or transient elastography combined with FLR volume for enhanced risk stratification. 3
Liver scintigraphy and MRI with hepatobiliary contrast agents may provide more informative assessments of functional liver reserve than CT volumetry alone, though they require specialized equipment and expertise. 3