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Liver Volumetry in Virtual Hepatectomy Must Account for Vascular Territories
1194
Letters
3. Leeper WR, Leeper TJ, Ouellette D, et al. Delayed hemorrhagic complications in the nonoperative management of blunt splenic trauma: Early screening leads to a decrease in failure rate. J Trauma Acute Care Surg 2014;76:1349e1353.
Disclosure Information: Nothing to disclose.
Clarification on Angiography and Embolization for Blunt Splenic Injuries In Reply to Livingston and colleagues Preston Miller, MD, Michael Chang, MD, Jason Hoth, MD, Nathan Mowery, MD, Amy Hildreth, MD, Shayn Martin, MD, James Holmes, MD, Wayne Meredith, MD, Jay Requarth, MD Winston Salem, NC We owe thanks to Drs Livingston, Moffat, Leeper, Parry, and Gray for giving us the opportunity to clarify some of the findings in our recent work on angiography and embolization for blunt splenic injuries. They are correct about the studied endpoints. Mortality examined was all cause, in-hospital mortality. Nonoperative management (NOM) was defined as management of a spleen injury without an initial plan for laparotomy for any reason. With respect to the concept of failure of NOM, we are referring to the requirement for laparotomy during planned nonoperative therapy. We did not use repeat angiography in any of the studied patients as a salvage method. No patient who had unsuccessful NOM died, but this is certainly a described risk that must be examined if it occurs. In evaluating the similarities and differences between the control and study periods, the evaluated parameters are listed in the article. No other characteristics were included in the analysis. This comparison was done to determine if there were important differences between the 2 groups that might explain the increase in NOM success independently of the increased angioembolization described. As is pointed out, the Injury Severity Score was higher in the earlier control group as compared with the study group. This is why we also highlighted the fact that the Injury Severity Score was similar in the patients who actually went on to have unsuccessful NOM in both groups. In closing, we appreciate these physicians’ thoughts on our work. We hope this represents one more step in the understanding of safer and more effective ways to avoid
J Am Coll Surg
laparotomy for splenic injury in appropriately selected patients. Disclosure Information: Nothing to disclose.
Liver Volumetry in Virtual Hepatectomy Must Account for Vascular Territories Yoshihiro Mise, MD, Thomas A Aloia, Jean-Nicolas Vauthey, MD Houston, TX
MD,
We read with interest the report by Simpson and colleagues1 regarding the accuracy of preoperative virtual hepatectomy in predicting remnant liver volume (RLV) in patients undergoing resection for liver tumors. In this report, the authors conducted 2 investigations. First, the accuracy of virtual hepatectomy in predicting RLV was assessed by comparing preoperative RLV estimates to postoperative RLV as calculated by CT algorithms. Second, the accuracy of computerized total liver volume (TLV) estimation was compared with that of morphometric equations commonly used in preoperative liver surgery planning. Unfortunately, in both of these experiments, there were conceptual and methodologic flaws that limited the ability of the study to demonstrate the full potential of virtual hepatectomy. The gold standard reference for any technology that aims to estimate liver volume is resected and remnant liver weight. This concept has been demonstrated in a study of living donor liver transplantation, in which virtual hepatectomy volume estimates of the hemiliver or right posterior sector were referenced against the actual weights of these specimens and correlated with volumes estimated on 2-dimensional CT volumetry.2 In this study by Simpson and associates,1 the authors used postoperative CT to calculate RLV, with 21% of scans obtained 7 days postsurgery, leading to overestimates of RLV because of early liver regeneration. A second methodologic flaw of the study was that flat planar liver transection lines were used to make a virtual division of the intended specimen from the remnant liver. This linear-cutting method does not accurately estimate RLV particularly after minor hepatectomy/segmentectomy (11 of 66 patients), because the territory of Couinaud’s segments is circumscribed by curvilinear planes based on vascular anatomy.3 Given these limitations, it is difficult to demonstrate the true capability of their virtual hepatectomy tool to inform surgical decision-making when a few percentage points of
Vol. 219, No. 6, December 2014
estimated RLV may make the difference between resection vs palliation and postoperative liver failure vs survival. With regard to the accuracy of TLV measurement, a clinically relevant tool must include some component of liver function. First, the algorithm must subtract the volume of space occupying tumor within the liver. By including the tumor volume in their calculation, the authors again introduced a critical bias that may invalidate comparison with traditional CT-based techniques.4 In addition, their unadjusted liver volume measurements do not account for the metabolic demands of each patient, which are best captured by adjusting for body surface area. Kawasaki and coworkers5 have demonstrated this in practice, showing that the volume of the transplanted liver in the recipient converged to the volume estimated by equations regardless of the initial size of the liver graft.5 Despite the inability of the Simpson study to clinically demonstrate the advantages of virtual hepatectomy over conventional 2-dimensional CT planning, we agree that as procedures become more complex, virtual hepatectomy will play an increasingly important role in liver surgery. However, without compensation for intrahepatic tumor volume and for patient body habitus, we fear that surgeons may be given a false sense of security by computer generated volume estimates that focus only on the raw liver volume and do not account for vascular territories. REFERENCES 1. Simpson AL, Geller DA, Hemming AW, et al. Liver planning software accurately predicts postoperative liver volume and measures early regeneration. J Am Coll Surg 2014;219:199e207. 2. Satou S, Sugawara Y, Tamura S, et al. Three-dimensional computed tomography for planning donor hepatectomy. Transplant Proc 2007;39:145e149. 3. Mise Y, Satou S, Shindoh J, et al. Three-dimensional volumetry in 107 normal livers reveals clinically relevant inter-segment variation in size. HPB (Oxford) 2014;16:439e447. 4. Vauthey JN, Chaoui A, Do KA, et al. Standardized measurement of the future liver remnant prior to extended liver resection: methodology and clinical associations. Surgery 2000; 127:512e519. 5. Kawasaki S, Makuuchi M, Ishizone S, et al. Liver regeneration in recipients and donors after transplantation. Lancet 1992;339:580e581.
Disclosure Information: Nothing to disclose.
Hepatic Resection Planning in the Modern Era In reply to Mise and colleagues Amber L Simpson, PhD, William R Jarnagin, MD, FACS,
Letters
Michael I D’Angelica, New York, NY
1195
MD, FACS
We welcome this opportunity to elaborate on these novel data and findings. Drs Mise, Aloia, and Vauthey’s claim, “the gold standard reference for any technology that aims to estimate liver volume is resected and remnant liver weight,” is inaccurate and misleading, given their own reports using imaging measurements as ground truth.1 Issues with intraoperative remnant weight estimates are well known2: the conversion factor for liver weight to volume is based on experimental data that indicate healthy liver parenchyma has a density similar to that of water (1 g water ¼ 1 mL water at 4 C); our patients were neither healthy nor cooled. Further, the weight of the resected specimen is under-reported due to lack of organ perfusion at the time of assessment. Three-dimensional (3-D) imaging-based methods provide precise organ measurement in situ and are the standard in volumetry studies,2,3 including Dr Vauthey’s own work. We agree that early regeneration between the time of surgery and postoperative imaging could potentially bias accuracy assessment, and this point is discussed at length in the manuscript. We compensated for this potential error by factoring the timing of the scan into the multiple linear regression analyses in the study, which modestly improved the overall fit of the actual and planned remnant liver volume from r ¼ 0.941 to r ¼ 0.953.4 These results suggest that the effect of early regeneration was small, consistent with the report from Pomfret and colleagues5 showing a 1.5% increase per day in liver volume from baseline to 1 week. We note that early postoperative scans are not routinely performed in the first week after surgery; in this study they were acquired at a median of 5 days due to the nature of the clinical trial. So this article describes scans timed much earlier than those in related work. With respect to the resection plane used to define the future liver remnant (FLR), the respondents fail to appreciate that the resection plane is a 2-dimensional (2-D) surface that can be manipulated in 3-D space. This capability is demonstrated in Figure 1 of the article, where a resection is performed with an irregular surface.4 To further pictorially demonstrate the flexibility of 3-D resection planning, demarcation of a left lateral sectionectomy is shown in Figure 1 (with this letter). Techniques for deriving 3-D objects from imaging data, manipulating and cutting 3-D objects, and calculating properties such as volume and surface area are well established and sophisticated beyond the “flat plane” that the discussants attribute to our study. These techniques have been the
Letters
3. Leeper WR, Leeper TJ, Ouellette D, et al. Delayed hemorrhagic complications in the nonoperative management of blunt splenic trauma: Early screening leads to a decrease in failure rate. J Trauma Acute Care Surg 2014;76:1349e1353.
Disclosure Information: Nothing to disclose.
Clarification on Angiography and Embolization for Blunt Splenic Injuries In Reply to Livingston and colleagues Preston Miller, MD, Michael Chang, MD, Jason Hoth, MD, Nathan Mowery, MD, Amy Hildreth, MD, Shayn Martin, MD, James Holmes, MD, Wayne Meredith, MD, Jay Requarth, MD Winston Salem, NC We owe thanks to Drs Livingston, Moffat, Leeper, Parry, and Gray for giving us the opportunity to clarify some of the findings in our recent work on angiography and embolization for blunt splenic injuries. They are correct about the studied endpoints. Mortality examined was all cause, in-hospital mortality. Nonoperative management (NOM) was defined as management of a spleen injury without an initial plan for laparotomy for any reason. With respect to the concept of failure of NOM, we are referring to the requirement for laparotomy during planned nonoperative therapy. We did not use repeat angiography in any of the studied patients as a salvage method. No patient who had unsuccessful NOM died, but this is certainly a described risk that must be examined if it occurs. In evaluating the similarities and differences between the control and study periods, the evaluated parameters are listed in the article. No other characteristics were included in the analysis. This comparison was done to determine if there were important differences between the 2 groups that might explain the increase in NOM success independently of the increased angioembolization described. As is pointed out, the Injury Severity Score was higher in the earlier control group as compared with the study group. This is why we also highlighted the fact that the Injury Severity Score was similar in the patients who actually went on to have unsuccessful NOM in both groups. In closing, we appreciate these physicians’ thoughts on our work. We hope this represents one more step in the understanding of safer and more effective ways to avoid
J Am Coll Surg
laparotomy for splenic injury in appropriately selected patients. Disclosure Information: Nothing to disclose.
Liver Volumetry in Virtual Hepatectomy Must Account for Vascular Territories Yoshihiro Mise, MD, Thomas A Aloia, Jean-Nicolas Vauthey, MD Houston, TX
MD,
We read with interest the report by Simpson and colleagues1 regarding the accuracy of preoperative virtual hepatectomy in predicting remnant liver volume (RLV) in patients undergoing resection for liver tumors. In this report, the authors conducted 2 investigations. First, the accuracy of virtual hepatectomy in predicting RLV was assessed by comparing preoperative RLV estimates to postoperative RLV as calculated by CT algorithms. Second, the accuracy of computerized total liver volume (TLV) estimation was compared with that of morphometric equations commonly used in preoperative liver surgery planning. Unfortunately, in both of these experiments, there were conceptual and methodologic flaws that limited the ability of the study to demonstrate the full potential of virtual hepatectomy. The gold standard reference for any technology that aims to estimate liver volume is resected and remnant liver weight. This concept has been demonstrated in a study of living donor liver transplantation, in which virtual hepatectomy volume estimates of the hemiliver or right posterior sector were referenced against the actual weights of these specimens and correlated with volumes estimated on 2-dimensional CT volumetry.2 In this study by Simpson and associates,1 the authors used postoperative CT to calculate RLV, with 21% of scans obtained 7 days postsurgery, leading to overestimates of RLV because of early liver regeneration. A second methodologic flaw of the study was that flat planar liver transection lines were used to make a virtual division of the intended specimen from the remnant liver. This linear-cutting method does not accurately estimate RLV particularly after minor hepatectomy/segmentectomy (11 of 66 patients), because the territory of Couinaud’s segments is circumscribed by curvilinear planes based on vascular anatomy.3 Given these limitations, it is difficult to demonstrate the true capability of their virtual hepatectomy tool to inform surgical decision-making when a few percentage points of
Vol. 219, No. 6, December 2014
estimated RLV may make the difference between resection vs palliation and postoperative liver failure vs survival. With regard to the accuracy of TLV measurement, a clinically relevant tool must include some component of liver function. First, the algorithm must subtract the volume of space occupying tumor within the liver. By including the tumor volume in their calculation, the authors again introduced a critical bias that may invalidate comparison with traditional CT-based techniques.4 In addition, their unadjusted liver volume measurements do not account for the metabolic demands of each patient, which are best captured by adjusting for body surface area. Kawasaki and coworkers5 have demonstrated this in practice, showing that the volume of the transplanted liver in the recipient converged to the volume estimated by equations regardless of the initial size of the liver graft.5 Despite the inability of the Simpson study to clinically demonstrate the advantages of virtual hepatectomy over conventional 2-dimensional CT planning, we agree that as procedures become more complex, virtual hepatectomy will play an increasingly important role in liver surgery. However, without compensation for intrahepatic tumor volume and for patient body habitus, we fear that surgeons may be given a false sense of security by computer generated volume estimates that focus only on the raw liver volume and do not account for vascular territories. REFERENCES 1. Simpson AL, Geller DA, Hemming AW, et al. Liver planning software accurately predicts postoperative liver volume and measures early regeneration. J Am Coll Surg 2014;219:199e207. 2. Satou S, Sugawara Y, Tamura S, et al. Three-dimensional computed tomography for planning donor hepatectomy. Transplant Proc 2007;39:145e149. 3. Mise Y, Satou S, Shindoh J, et al. Three-dimensional volumetry in 107 normal livers reveals clinically relevant inter-segment variation in size. HPB (Oxford) 2014;16:439e447. 4. Vauthey JN, Chaoui A, Do KA, et al. Standardized measurement of the future liver remnant prior to extended liver resection: methodology and clinical associations. Surgery 2000; 127:512e519. 5. Kawasaki S, Makuuchi M, Ishizone S, et al. Liver regeneration in recipients and donors after transplantation. Lancet 1992;339:580e581.
Disclosure Information: Nothing to disclose.
Hepatic Resection Planning in the Modern Era In reply to Mise and colleagues Amber L Simpson, PhD, William R Jarnagin, MD, FACS,
Letters
Michael I D’Angelica, New York, NY
1195
MD, FACS
We welcome this opportunity to elaborate on these novel data and findings. Drs Mise, Aloia, and Vauthey’s claim, “the gold standard reference for any technology that aims to estimate liver volume is resected and remnant liver weight,” is inaccurate and misleading, given their own reports using imaging measurements as ground truth.1 Issues with intraoperative remnant weight estimates are well known2: the conversion factor for liver weight to volume is based on experimental data that indicate healthy liver parenchyma has a density similar to that of water (1 g water ¼ 1 mL water at 4 C); our patients were neither healthy nor cooled. Further, the weight of the resected specimen is under-reported due to lack of organ perfusion at the time of assessment. Three-dimensional (3-D) imaging-based methods provide precise organ measurement in situ and are the standard in volumetry studies,2,3 including Dr Vauthey’s own work. We agree that early regeneration between the time of surgery and postoperative imaging could potentially bias accuracy assessment, and this point is discussed at length in the manuscript. We compensated for this potential error by factoring the timing of the scan into the multiple linear regression analyses in the study, which modestly improved the overall fit of the actual and planned remnant liver volume from r ¼ 0.941 to r ¼ 0.953.4 These results suggest that the effect of early regeneration was small, consistent with the report from Pomfret and colleagues5 showing a 1.5% increase per day in liver volume from baseline to 1 week. We note that early postoperative scans are not routinely performed in the first week after surgery; in this study they were acquired at a median of 5 days due to the nature of the clinical trial. So this article describes scans timed much earlier than those in related work. With respect to the resection plane used to define the future liver remnant (FLR), the respondents fail to appreciate that the resection plane is a 2-dimensional (2-D) surface that can be manipulated in 3-D space. This capability is demonstrated in Figure 1 of the article, where a resection is performed with an irregular surface.4 To further pictorially demonstrate the flexibility of 3-D resection planning, demarcation of a left lateral sectionectomy is shown in Figure 1 (with this letter). Techniques for deriving 3-D objects from imaging data, manipulating and cutting 3-D objects, and calculating properties such as volume and surface area are well established and sophisticated beyond the “flat plane” that the discussants attribute to our study. These techniques have been the