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Standard and modified techniques for parenchyma-preserving hepatectomy focused on segments I+IV resection in patients with perihilar cholangiocarcinoma

Resection of the hepatic segments I+IV (S1+S4) is the most common type of parenchyma-preserving hepatectomy (PPH) for perihilar cholangiocarcinoma (PHCC). The author describes personal experience on the standard and modified techniques for PPH focused on S1+S4 resection in patients with PHCC. 1) Isolated caudate lobectomy with bile duct resection (BDR) is the minimal type of PPH, but not currently recommended due to technical difficulty. 2) Partial hepatectomy of S1+S4a±segment V (S5) with BDR provides wide operative field, but extension of BDR is limited and resection of S1 paracaval portion is still difficult. 3) Resection of S1+S4+S5 with BDR provides wider operative field for complete S1 resection and multiple biliary reconstruction. 4) Resection of S1+S4 with BDR offers very wide operative field and allows wider extent of hilar BDR, and thus presents the most common type of PPH. A supplementary video clip presents the detailed standard surgical procedure for resection of S1+S4 with BDR in a patient with type IIIA PHCC. 5) Modified resection of S1+S4±S5 or segment VIII (S8) with BDR facilitates additional resection of tumor-involved S5 or S8 ducts. 6) Major hilar vascular invasion is usually contraindicated for PPH and only small portal vein invasion requiring wedge resection and patch venoplasty is allowed. In conclusion, PPH can achieve curative resection and improved outcomes in patients with PHCC via reasonable modification of the extent of hepatectomy and hilar BDR. PPH may have advantages in selected patients depending on the extent of tumor, and in patients with high operative risk.


INTRODUCTION
Extended hepatectomy enhances the surgical curability through obtaining tumor-free bile duct resection margins (BDRMs) compared with local resection in patients with perihilar cholangiocarcinoma (PHCC). [1][2][3][4][5][6][7] However, extended hepatectomy can increase postoperative morbidity and mortality because it often entails massive liver resection which is strongly associated with post-hepatectomy liver failure (PHLF) and hepatic decompensation. [8][9][10] Thus, parenchyma-preserving hepatectomy (PPH) can be considered as an alternative hepatectomy if extended hepatectomy carries a high risk of PHLF. 10 Resection of the hepatic segments I+IV (S1+S4) is the most common type of PPH for PHCC. PPH has been usually indicated for selected patients in whom curative resection is expected through PPH because PPH may result in lower surgical curability compared with extended hepatectomy. However, in practice, the decision to determine surgical curability for PHCC is often difficult before or even during surgery.
The cumulative experience involving PHCC has led to the expansion of indications for PPH because the extent of hilar bile duct resection (BDR) can be increased toward the left, right or both liver sides in order to obtain tumor-free BDRMs. 11 The author describes personal experience with the standard and modified techniques for PPH focused on S1+S4 resection in patients with PHCC.

Isolated caudate lobectomy with BDR
Considering the tumor invasion process in PHCC, it is mandatory to resect the caudate lobe (S1) in combination with various extents of hepatectomy. 3 The author previously reported isolated S1 resection with BDR in a patient with Bismuth-Corlette type IV PHCC. 12 The operative field during and after isolated S1 resection was very narrow, thus multiple hepaticojejunostomies for the 3 right and 4 left hepatic duct openings was very demanding ( Fig. 1). Because of such technical challenges and the high risk of biliary reconstruction-associated complications, this technique was no longer recommended.

Partial hepatectomy of segments I+IVa±V with BDR
To address the technical difficulty encountered during isolated S1 resection with BDR, the ventral portion of segment IV (S4a) with or without the ventral portion of segment V (S5) was concurrently resected. Such partial resection of S1+S4a±S5 widened the operative field, which facilitated S1 resection and multiple biliary reconstruction ( Fig. 2). However, it is usually indicated only for cases involving type I or II PHCC due to the limited extension of the BDRMs and difficult resection of the S1 paracaval portion.
Resection of segments I+IVa+V (S1+S4a+S5) with BDR S1+S4a+S5 resection along with BDR facilitates complete S1 resection and biliary reconstruction via wide operative field. 13 This technique entails transection of the middle hepatic vein (MHV), and thus designated as Taj Mahal resection due to the shape of hepatic resection.
However, it induced detrimental hepatic venous congestion at the MHV drainage territory in the right anterior section. To prevent such unnecessary hepatic venous congestion, the author reported S1+S4a+S5 resection with BDR after preservation of the MHV trunk (Fig. 3). 14 This procedure yielded wider operative field for complete S1 resection and multiple biliary reconstructions.

Resection of segments I+IV (S1+S4) with BDR
Complete transection of the liver into right and left livers provides very wide operative field and allows wider  hilar BDR, which is an advantage for complete S1 resection and multiple biliary reconstruction; it also enables expansion of the extent of BDRMs deep into the right and left liver sides. Resection of the S1+S4 is the simplest and most effective PPH (Fig. 4). 15 The extent of hilar BDR is compatible with that of right trisectionectomy on the side of left hepatic duct and that of left hepatectomy toward the right hepatic duct. Due to very wide operative

Modified resection of segments I+IV±V/VIII (S1+4±5/8) with BDR
Depending on the extent of tumor invasion, the extent of S1+S4 resection can be non-anatomically expanded to obtain tumor-free BDRMs. When the right anterior or posterior bile duct was extensively involved, the medial part of the right anterior section was further transected to remove the involved segment V ducts (B5) or segment VIII ducts (B8s) (Fig. 6). 12 The middle hepatic vein trunk can also be resected to match the additional partial re-  section of the right anterior section (Fig. 6). formed during PPH (Fig. 7), but it is strongly contraindicated because of the complexity of the surgical procedures and disappointing postoperative outcomes. Conversely, small-sized portal vein invasion requiring only wedge resection and patch venoplasty (Fig. 7B) (Fig. 9A).

Concurrent resection of hilar vascular invasion during S1+S4 resection with BDR
The liver surface was marked to define the territory of hepatic resection (Fig. 9B). The right-sided hepatic parenchymal transection was performed along the hemi-liver discoloration line ( Fig.   10A). At the right hepatic hilum, two segment V ducts (B5s) and two segment VIII ducts (B8s) were transected (Fig. 10B), and were found tumor-free. The right posterior duct, a conjoined portion of the segment VI and VII ducts (B6+7) was transected, which was also tumor-free. The paracaval portion of S1 combined with the Spigelian lobe was removed along with S4 resection (Fig. 10C, D).
The two B5s and two B8s openings were placed within the common connective tissue sheath, which was sepa-  rated from a single B6+7 opening. Thus, unification ductoplasty was performed to conjoin these right-sided ducts (Fig. 11A). The 4-cm-wide conjoined right hepatic duct was reconstructed through a single hepaticojejunostomy ( Fig. 11B, C). The three hepatic duct openings at the left lateral section (one B2, one B3 and one remnant B4) were also within the common connective tissue sheath, thus obviating the need for ductoplasty. A single hepaticojejuno- The patient recovered uneventfully (Fig. 8D) and was discharged from the hospital on the postoperative day 21.
Because of poor general condition and patient's refusal, the patient did not receive adjuvant chemotherapy. Multiple recurrences occurred 16 months after surgery, and the patient passed away 24 months after surgery due to tumor progression.

DISCUSSION
It is important to obtain tumor-free resection margin during the surgical treatment of PHCC. 5,16 Extended hepatectomy has been preferred to achieve curative resection of PHCC because it facilitates tumor-free BDRMs and is also effective to manage major hilar vascular invasion.
However, the majority of patients with PHCC manifest obstructive jaundice, which decreases the hepatic functional reserve, even after sufficient biliary decompression.  4 Because S1 resection is known to be a prerequisite for curative resection of PHCC, 20 resection of the entire S1 can be the most limited PPH in surgical resection for PHCC. 12 Various combinations of S1 resection with S4 and S5 resection are presented in the present study. [13][14][15] Of them, S1+S4 resection appears to be the most reasonable extent of PPH for patients with PHCC after considering the complexity of surgical procedures and the extent of hilar BDR. 15 The parenchymal resection rate through S1+S4 resection is estimated to be approximately 10%-15% of the whole liver volume.
No standardized surgical procedures of S1+S4 resection