[Estimation of the parenchymal reserve-Volumetric and functional before resection]

The preoperative estimation of the volumetric and especially functional future liver remnant (FLR) is of particular importance before major liver resections to avoid posthepatectomy liver failure (PHLF). A postoperative regeneration of the liver is only possible if there is sufficient functional FLR. Laboratory parameter scores, such as the combined aspartate aminotransferase to platelet ratio index (APRI)/albumin-bilirubin grade (ALBI) score, can provide an initial assessment of the risk of PHLF. Other functional tests, such as the ICG-R15 test, the LiMAx® (Humedics GmbH, Berlin, Germany) test or scintigraphic procedures (e.g. technetium 99m mebrofenin secretion) can be used in the event of abnormal findings in order to assess liver function more precisely. In the case of inhomogeneous parenchymal quality, for example after portal vein embolization (PVE), knowledge of the segmental functional distribution is essential. This can be done by functional imaging techniques, such as the technetium 99m mebrofenin scintigraphy examinations in combination with magnetic resonance imaging (MRI). Although not yet approved for functional testing, MRI with the hepatocyte-specific contrast agent gadolinium provides a practicable surrogate parameter for parallel three-dimensional (tumor) imaging. This procedure is already well validated. In the future, deep learning algorithms will enable automated analyses of segmental liver function; however, surgical expertise remains decisive for assessing resectability. As a guideline the rule of thumb is at least 30% parenchymal reserve in patients with a healthy liver and 40% in risk constellations. This article provides an overview of current concepts and diagnostic procedures for the preoperative assessment of sufficient parenchymal reserve.