Effectiveness of Intraoperative Facial Nerve Monitoring in Submandibular Gland Surgery: A Retrospective Study of a Single Institution.

Background: Intraoperative facial nerve monitoring (IFNM) is becoming increasingly prevalent as an established intraoperative aid in parotid gland surgery. To date, however, there are few scientific studies on the postoperative outcomes of submandibular gland surgery, particularly on the postoperative injury of the marginalis mandibulae branch (MMB) of the facial nerve (FN). This branch represents the most frequent and feared complication of this surgery, with an incidence of 1-7% of cases.

Objective: This retrospective study aims to evaluate the incidence of postoperative MMB paralysis in patients undergoing submandibular sialoadenectomy for benign conditions from 2014 to 2023, focusing on the role of IFNM.

Materials and methods: The patients were divided into two groups: the subjects of Group 1 (G1) had undergone submandibular sialoadenectomy after identification and clamped facial vessels, without the aid of IFNM (from 1 January 2014 to 31 December 2018). Conversely, subjects in Group 2 (G2) underwent IFNM procedures (from 1 January 2019 to 31 December 2023). The classification of any FN malfunctions was conducted following the House-Brackmann grading system. A descriptive analysis was performed, and univariate and multivariate logistic regressions were used to examine the impact of IFNM on surgical timing and the association between G2 deficit (vs. G1) corrected for age, sex, and smoking status.

Results: The study population comprised a total of 101 patients with a mean age of 55 ± 16 years. The sample population comprised 50 subjects assigned to Group 1 (49.5%, 24 females and 26 males) and 51 subjects assigned to Group 2 (50.5%, 21 males and 30 females). Postoperative paralysis of the MMB occurred in 23 subjects (22.77%), including 12 of G1 (4 had a grade II and 8 grade III dysfunction) and 11 of G2 (8 had a grade II and 3 grade III dysfunction). A six-month evaluation revealed that only five patients in G1, previously diagnosed with grade II dysfunction, exhibited a residual deficit. The mean surgical time for the entire patient cohort was 99 ± 44 min: 110 ± 43 min for Group 1 and 92 ± 42 min for Group 2 (Beta = -19; 95% CI -37 at -0.16; p-value = 0.048). Furthermore, a longer operative time was observed in smokers than in non-smokers (p-value = 0.008), suggesting that smoking affects the length of surgery (Beta = 0.32; 95% CI -0.08 to -0.55).

Discussion and conclusions: MMB paralysis is one of the most prevalent complications that may arise in submandibular gland surgery. IFNM provides surgeons with a valuable tool for identifying MMB in submandibular sialoadenectomy. The efficacy of IFNM as an aid is contingent upon the expertise of the operating surgeon.