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Page 6 of 8 Kobayashi et al. Mini-invasive Surg 2020;4:30 I http://dx.doi.org/10.20517/2574-1225.2020.12

Short-term surgical results obtained using the modified surgical technique
There were no differences between the conventional and modified surgery groups in terms of sex, age,
body mass index, tumor histology and location, clinical stage, preoperative therapy, physical status, and
other preoperative risks [Table 1]. None of the cases required conversion to open surgery and there was
no intraoperative morbidity in either group. In the modified surgery group, the operation was performed
robotically, which significantly shortened the procedure compared to the conventional surgery group
(266 min vs. 295 min, P = 0.04). There was no significant difference in the estimated total volume of blood
loss between groups, although it tended to be lower in the modified surgery group (91 mL vs. 150 mL,
P = 0.08). The number of dissected mediastinal lymph nodes was significantly higher in the modified
surgery group (29 vs. 24, P = 0.04). There were also no differences in the rates of complications such as
RLNP, aspiration, pneumonia, and anastomotic leakage between the two groups. However, the rate of
RLNP tended to be lower in the modified surgery group than in the conventional surgery group (5% vs.
17.5%). The median length of postoperative hospital stay was the same between groups (22 days).

DISCUSSION
RLNP is a relatively frequent complication of esophageal cancer surgery that affects the postoperative
[1,8]
course and even overall survival . There are several reports describing the effectiveness of IONM to
prevent postoperative RLNP following esophagectomy [9-11] . At our hospital, the incidence of RLNP has
declined since we introduced IONM but it has not been completely eliminated.

The surgical procedure(s) that lead to RLNP remain unclear, and there have not been reports to date
addressing this point. In general, the cause was presumed to be either thermal injury from an energy
device, or damage through nerve traction or compression. However, without identifying the cause, it is
very difficult to implement effective preventive measures. On the other hand, IONM has long been used
[12]
in the field of Otolaryngology in the treatment of thyroid cancer and there are many reports on the
causes of RLNP after thyroid surgery [13-15] , with traction accounting for 75%-83% of cases. In this study,
we found that RLNP following esophageal cancer surgery was similarly, primarily caused by traction and
compression, with little contribution from thermal injury. This is the first report describing the causes of
RLNP associated with esophageal cancer surgery, albeit in a small number of cases.

We have developed a modified surgical technique to prevent RLNP. Thermal injury occurred relatively
early in the surgery and can be prevented by examining the location of the nerve by IONM. In recent
years, mesentery-oriented lymph node dissection has become commonplace and has been proposed
[16]
[6,8]
for esophagectomy . Accordingly, we dissected the lymph nodes after mesenterization . However,
this inevitably increased the risk of strongly pulling the RLN, which could result in RLNP. We therefore
concluded that it was difficult to prevent RLNP by this method (conventional surgery group, Figure 3).

The modified surgical technique is suitable for dissecting lymph nodes around the RLN with minimal
retraction and compression and has in fact, reduced the rate of RLNP at our institution [Table 1]. Of the 20
surgeries performed after standardizing the procedure, there was only one case of RLNP in which the RLN
was seized after misidentification, which counts as a technical error. There have been no instances of RLNP
since due to an unidentified cause.

Robot-assisted minimal invasive surgery (Ra-MIE) was used in the modified surgery group for historical
reasons. Approved as a medical treatment in Japan since 2018, Ra-MIE is advantageous in esophageal
cancer surgery because it allows the operator to manipulate three arms in a stable field of view, even within
a narrow space such as the upper mediastinum. Ra-MIE is particularly useful for the delicate manipulation
required around the RLN. Thus, Ra-MIE undoubtedly contributed to the impressive results achieved with
our modified surgical procedure. However, when comparing 33 Ra-MIE and 44 thoracoscopic surgeries,