How much liver needs to be transected in ALPPS? A translational study investigating the concept of less invasiveness

Background. ALPPS induces rapid liver hypertrophy after stage-1 operation, enabling safe, extended resections (stage-2) after a short period. Recent studies have suggested that partial transection at stage-1 might be associated with a better safety profile. The aim of this study was to assess the amount of liver parenchyma that needs to be divided to achieve sufficient liver hypertrophy in ALPPS. Methods. In a bi-institutional, prospective cohort study, nonfibrotic patients who underwent ALPPS with complete (n = 22) or partial (n = 23) transection for colorectal liver metastases were analyzed and compared with an external ALPPS cohort (n = 23). A radiologic tool was developed to quantify the amount of parenchymal transection. Liver hypertrophy and clinical outcome were compared between both techniques. The relationship of partial transection and hypertrophy was investigated further in an experimental murine model of partial ALPPS. Result. The median amount of parenchymal transection in partial ALPPS was 61 % (range, 34-86%). The radiologic method correlated poorly with the intraoperative surgeon's estimation (r(s) = 0.258). Liver hypertrophy was equivalent for the partial ALPPS, ALPPS, and external ALPPS cohort (64% vs 60% vs. 64%). Experimental data demonstrated that partial transection of at least 50% induced comparable hypertrophy (137% vs 156%) and hepatocyte proliferation compared to complete transection. Conclusion. The study provides clinical and experimental evidence that partial liver partition of at least 50% seems to be equally effective in triggering volume hypertrophy as observed with complete transection and can be re recommended as less invasive alternative to ALPPS.