Main outcome indicators
3.1 Postoperative nerve damage
Seven of the studies described postoperative nerve
damage15-21, which was transient and resolved during
the follow-up. In this meta-analysis, postoperative nerve damage was
divided into transient greater auricular nerve damage and other nerve
damage, including the marginal mandibular branch of the facial nerve,
lingual nerve, and hypoglossal nerve. Transient auricular nerve damage
mainly manifested as temporary earlobe numbness. Damage to the marginal
mandibular branch of the facial nerve, lingual nerve, and hypoglossal
nerve was indicated by crookedness of the corners of the mouth, tongue
tip numbness, and tongue deviation on extension, respectively.
3.1.1 Temporary earlobe numbness
Four of the eight studies reported the occurrence of temporary
postoperative earlobe numbness15, 16, 18, 21. The
studies included 161 patients; 73 and 88 in the retroauricular hairline
and conventional approach groups, respectively. There were seven cases
of temporary earlobe numbness, all in the retroauricular hairline group.
The difference in temporary postoperative earlobe numbness between the
two surgical approaches was statistically significant (OR: 7.28; 95%
CI: 1.57–33.87; P = 0.01; Fig. 2). There was no significant
heterogeneity among the studies (χ2 = 0.16, df = 3, P
= 0.98, I2 = 0%; Fig. 2). This indicated that
submandibular gland excision through the retroauricular hairline
approach increases the risk of temporary earlobe numbness, but this
resolves during the follow-up.
3.1.2 Other nerve damage
Transient damage to the marginal mandibular branch of the facial nerve,
lingual nerve, and hypoglossal nerve was described in seven of the
studies15-21, with a total of 270 patients; 114 and
156 in the retroauricular and conventional approach groups,
respectively. There was no statistically significant difference between
the two surgical approaches (OR: 0.80; 95% CI: 0.38–1.71; P = 0.57;
Fig 3). This indicates that the two surgical approaches had similar
incidences for damage to the marginal mandibular branch of facial nerve,
lingual nerve, and hypoglossal nerve.
The incidences of nerve injury in
both the conventional and retroauricular groups in the Carlos 2019 study
[20] were close to 50%, however, all symptoms disappeared during
the follow-up period. When the results of this study were excluded, the
results remained statistically insignificant between the two surgical
approaches (OR: 0.77; 95% CI: 0.24–2.40; P = 0.65; Fig 12).