A 52-year-old male with no significant past medical history presented with upper abdominal fullness and abnormal liver tests, with alkaline phosphatase 492, ALT 163, and bilirubin 1.4. CEA and CA19-9 were normal. MR showed a 20 cm multiloculated cyst involving segments 4/5/8 and compressing but not invading the left and right anterior portal structures (Fig. 3.2a–d). There was no evidence of portal hypertension.

Based on the smooth, well-defined border of the cyst with compression but with no evidence of invasion of portal structures, central resection in the enucleation plane of the lesion was undertaken. After taking down the gallbladder, tying and dividing the gallbladder mesentery, and lowering the portal bifurcation in an extra-Glissonian plane, the segment 4 structures were dissected and ligated in the umbilical fissure. The capsule of the liver was scored with electrocautery around the edge of the cyst. The porta hepatis was occluded en masse with a broad vascular clamp for 19 min, during which the cyst was separated from segments 2–3 in the enucleation plane using scissors dissection, clipping vessels, and ducts that traversed the transection plane with a multiclip applier. After a 5-minute period of reperfusion, the porta was once again clamped for 20 min, during which the cyst was similarly enucleated away from segments 5–8. The main trunk of the middle hepatic vein, which was closely applied onto the cyst, was ligated at its junction with the left hepatic vein and removed along with the specimen.

The patient had an uneventful recovery and was discharged home on postoperative day 4. Pathology revealed an 18 cm hepatobiliary mucinous cystadenoma with areas of carcinoma; extensive necrosis, cystic degeneration, and limited lymphovascular invasion were noted. No adjuvant therapy was given. The patient was alive and free of recurrence at 2 years after surgery.

Segment 4 is commonly described as having two subsegments, 4A and 4B, although there are typically multiple portal branches to segment 4 rather than two discrete pedicles. Be that as it may, the left portal vein runs transversely to the umbilical fissure under segment 4B and then up the umbilical fissure, terminating in the obliterated umbilical vein, often designated as the round ligament. The segment 4 portal branches, along with those from the hepatic artery and hepatic duct, enter segment 4 in the umbilical fissure and course through segment 4 from left to right (see Fig. 3.3). These portal structures are readily clipped or ligated in the umbilical fissure when complete resection of segment 4 or 4B is planned, but the fact that they run from left to right makes it possible to divide through segment 4 at any distance from the umbilical fissure without preliminary dissection while maintaining perfusion and biliary drainage to the portion of segment 4 that is left behind [10]. As they approach the liver, the portal vein, hepatic artery, and bile duct are invested and subsequently distributed through the liver within a common sheath derived from the reflection of Glisson’s capsule, and in many circumstances dissection of these structures in the extra-Glissonian plane is both the most expedient and the safest approach [10]. Separating the portal structures away from the parenchyma of segments 4B and 5 is a key maneuver when complete resection of these segments is planned. This so-called lowering of the hilar plate is accomplished by first removing the gallbladder if present, ligating and dividing the tissue at the base of the gallbladder fossa (commonly called the gallbladder mesentery; there are often small structures there that are of no consequence, but that can be troublesome if not ligated), dividing the peritoneum under segments 4B and 5 as it envelopes the portal structures, and separating the portal structures from the liver parenchyma outside of Glisson’s sheath. It typically requires the division of a few small portal branches near the portal bifurcation to establish this extra-Glissonian plane. While this process of lowering the hilar plate can be carried out with simple scissors dissection, an ultrasonic dissector, when available, is a useful tool to establish and maintain the correct plane of dissection.