Electric Knife

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ORIGINAL ARTICLE

Safety and usefulness of an electric knife during surgery for parotid benign tumor: postoperative facial paresis and its risk factors

RYO KAWATA, KOTETSU LEE, MICHITOSHI ARAKI & HIROSHI TAKENAKA

Department of Otolaryngology, Osaka Medical College, Osaka, Japan

AbstractConclusion. The incidence of facial nerve paresis was not high compared with previously reported incidences using

conventional operative techniques, showing the safety of the use of an electric knife in this operative technique. An electricknife is provided in almost all operating rooms and no special apparatus is necessary for this technique. Background . Sincethe glandular tissue of the parotid gland is rich in blood flow, safe and accurate protection of the nerve is often made difficultdue to bleeding during parotid surgery. Therefore, we developed a technique in which glandular tissue is cut using anelectric knife, which is provided in almost all operating rooms. Patients and methods. In this study, the safety and usefulnessof an electric knife in parotid surgery were confirmed by evaluating patients with parotid benign tumor who underwentsurgery using an electric knife. The subjects were 135 patients with parotid benign tumors. Results. Postoperative facialnerve paresis developed in 36 (26.6%) of the 135 patients but was transient in all cases. Depending on the tumor site,transient paresis was observed in 8 of the 13 patients with tumors in the deep lobe but in 28 (22.9%) of the 122 patients withtumors in the superficial lobe. The mean recovery time from facial nerve paresis was 6.1 weeks.

Keywords: Parotidectomy, facial paresis, surgical technique, electric knife

Introduction

Partial parotidectomy is the basic technique used for

surgery of parotid benign tumors [1 Á 3]. In this

technique, the main trunk of the facial nerve is

confirmed, and each branch is followed and pre-

served while parotid tissue is cut. However, since

glandular tissue is rich in blood flow, the safe and

accurate protection of the nerve is often difficult due

to bleeding. Cold knife dissection may lead to

multiple minor bleedings, which in turn may obscure

visualization of the course of the nerve and require

frequent replacement of the operating tools for

dissection and coagulation, leading to prolongedsurgery. There are various reports of surgical tech-

niques for parotid gland surgery, e.g. bipolar scissors

[4], water-jet dissection [5], and diathermy scissors

[6]. However, not all institutions have these special

tools. Therefore, we developed a technique in which

glandular tissue is cut using an electric knife [7],

which is provided with almost all operating rooms.

In this technique, the facial nerve should be carefully

protected during cutting of glandular tissue usingthe electric knife. In this study, we examined the

benefits and safety as well as the complications that

can result from the use of electric scissors to

determine whether it is a suitable tool for parotid

gland surgery.

Patients and methods

Patients

The subjects were 135 patients (70 male and 65

female) with parotid benign tumors who underwentsurgery at our department between September 1999

and July 2006. Their mean age was 57.3 years.

Histopathologically, Warthin tumors were observed

in 60 patients, pleomorphic tumors in 59, cysts in

11, and other benign tumors in 5. The tumor was

located in the superficial lobe in 122 patients and in

the deep lobe in 13. All operations were performed

by a single surgeon (R.K.).

Correspondence: Ryo Kawata, MD, Department of Otolaryngology, Osaka Medical College, 2-7 Daigaku-Cho Takatsuki, Osaka 569-8686, Japan. Tel: '81

72 683 1221. Fax: '81 72 684 6539. E-mail: [email protected]

Acta Oto-Laryngologica, 2007; 127: 966 Á 969

(Received 15 September 2006; accepted 29 October 2006)

ISSN 0001-6489 print/ISSN 1651-2551 online # 2007 Taylor & Francis



Surgical technique

Surgery was performed under general anesthesia. No

muscle relaxant was used, so that movements of the

facial muscle due to the electric knife could be

observed. Superficial parotidectomy was performed

for superficial lobe tumors, while subtotal paroti-

dectomy was performed with preserved facial nervewhen a benign tumor arose in the deep lobe.

An S-pattern skin incision was made, the operative

field was exposed by a routine method, and the

tragal pointer was exposed. The main trunk of the

facial nerve was identified using the mastoid process,

digastric muscle, and the tragal pointer as references.

Subsequently, glandular tissue was cut using an

electric knife by the following procedures. The

electric knife was used in the mixture mode of

incision and coagulation (each 35 W).

1. Surgical scissors were inserted along the ar-rangement of the facial nerve. ‘Following the

facial nerve’ is important, as insertion apart

from the nerve causes bleeding (Figure 1A).

2. An elevating hook was applied to the area cut

using the scissors, and the glandular tissue was

elevated (Figure 1B).

3. An assistant held the elevating hook while the

operator compressed the nerve to a deep area

using a nerve protection spatula (Figure 1C).

4. Glandular tissue bilaterally present between the

elevating hook and the nerve protection spatula

was cut using an electric knife. The middle area

between the elevating hook and nerve protec-

tion spatula was cut. It is important to cut

glandular tissue sharply with an electric knife in

the same manner as a cold knife (Figure 1D).

By the above procedure, glandular tissue was

dissected along the facial nerve. An approximately1 cm area can be dissected by performing the above

procedure once. The order of nerve branches

followed depends on the tumor site, but generally

the mandibular marginal branch is the first followed.

When the electric knife approached the facial

nerve for cutting of glandular tissue, the facial

muscle contracted due to current spread. However,

this presents no problem, and with experience, the

distance between the knife and nerve can be

estimated based on the degree of contraction of the

facial muscle. Therefore, to allow constant checking

of facial nerve contraction, care was taken not toplace the clean sheet over the face on the operation

side.

Elevating hooks and nerve protection spatulas

treated by a non-electrical conduction coating were

used, so that even if the electric knife were to touch

these instruments, they would not conduct electri-

city.

Neither a microscope nor a magnifying glass was

used in this technique. Intraoperative facial nerve

monitoring was not performed in any of the cases.

The electric knife can also play the role of facial nerve

monitoring because the operation was performed

Figure 1. (A) Surgical scissors were inserted along the arrangement of the facial nerve. (B) An elevating hook was applied to the area cut

with the scissors, and glandular tissue was elevated. (C) The operator compressed the nerve to a deep area using a nerve protection spatula.

(D) Glandular tissue bilaterally present between the elevating hook and the nerve protection spatula was cut using an electric knife.

Electric knife for parotid surgery 967



without the use of muscle relaxant. We also use the

electric knife for facial nerve monitoring, while safely

protecting the facial nerve.

Statistical analysis

Statistical analysis of the data was performed using JMP software (version 6.0.2, SAS Institute Inc.).

Pearson’s x2 test and Fisher’s exact probability test

were used for comparisons of categorical variables,

and the Student’s t test for numerical variables. The

significance level was set at B0.05.

Results

In the 135 patients, the mean operation time was

122 minutes, and mean blood loss was 39 ml.

Postoperative facial nerve paresis (i.e. any objective

facial weakness) developed in 36 (26.7%) of the 135

patients but was transient in all of them. The paresis

involved only the mandibular marginal branch

(lower lip) in 31 of the 36 patients but also involved

the zygomatic and buccal branches in the other 5.

According to histological types, transient paresis was

observed in 19 (32.2%) of the 59 patients with

pleomorphic adenoma but 13 (21.7%) of the 60

patients with Warthin tumor. As to tumor sites,

transient paresis was observed in 8 of the 13 patients

with tumors in the deep lobe but in 28 (23.0%) of

the 122 patients with tumors in the superficial lobe.

Evaluation of the possible association between tumor

size and transient paresis showed a mean tumordiameter of 27.9 mm in the patients with paresis and

26.1 mm in those without paresis. Sex, age, opera-

tion time, bleeding volume, and tumor size showed

no significant differences between cases with and

without paresis (Table I). The mean recovery period

from transient paresis was 6.1 weeks:B2 weeks in 2

patients, 2 Á 3 weeks in 3, 3 Á 4 weeks in 11, 4 Á 8

weeks in 9, 8 Á 12 weeks in 10, and 12 Á 24 weeks in 1

(Figure 2). Salivary fistulae were not observed in any

patient.

Discussion

In parotid surgery, surgical scissors and forceps

such as the mosquito are used for the procedure

around the facial nerve [8]. The advantage of the useof an electric knife for this procedure is minimized

bleeding. Minimal bleeding not only reduces the

operation time and total blood loss but also provides

a clear operative field, which is advantageous for

accurate protection of the facial nerve. The sight of

the facial nerve arrangement is often lost due to

bleeding. One possible problem of the use of an

electric knife is stimulation of the nerve due to

current spread when the electric knife is used near

the facial nerve. Whether this causes facial nerve

paresis is a concern. Therefore, the incidence of

facial nerve paresis after parotid surgery using anelectric knife was evaluated. The overall incidence

was 26.6%, but the incidence in patients with

tumors in the superficial lobe was 22.9%. The

incidence of facial nerve paresis after surgery for

parotid benign tumors has been reported to be 25 Á

43% [9 Á 12], which is similar to our incidence. In

addition, postoperative facial nerve paresis was

transient in all 36 patients, and the recovery period

was 1 Á 24 weeks (mean 6.1 weeks) (Figure 2). These

results suggest no association between the use of

Table I. Characteristics of postoperative facial paresis.

Parameter Facial paresis Á negative (n099) Facial paresis Á positive (n036) p value

Male:female 55:44 15:24 0.153

Age 57.0914.2 57.7912.4 0.795

Histopathology 0.194

Pleomorphic adenoma (59) 40 (68%) 19 (32%)

Warthin tumor (60) 47 (78%) 13 (22%)

Tumor site 0.006

Superficial lobe (122) 94 (77%) 28 (23%)

Deep lobe (13) 5 (38%) 8 (62%)

Operation time (min) 121.7930.9 122.1928.5 0.487

Bleeding volume (ml) 37.6930.5 40.8926.4 0.579

Tumor size (mm) 26.199.3 27.999.5 0.342

0

2

4

6

8

10

12

2 2–3 3–4 4–8 8–12 12–24

week

c a s e

Figure 2. Recovery period from postoperative transient facial

nerve paresis.

968 R. Kawata et al.



an electric knife and postoperative facial nerve

paresis.

When glandular tissue was cut using an electric

knife, no suture with thread was performed. How-

ever, postoperative salivary fistulae were not ob-

served in any patients, suggesting no association

between glandular cutting using an electric knife andsalivary fistulae.

Previously reported risk factors of postoperative

facial nerve dysfunction for primary benign diseases

include the patient’s age, surgeon’s experience,

tumor size, operation time, tumor site, histological

type, and inflammatory conditions [10 Á 14]. In our

study, we found that the tumor site was the most

important factor associated with facial nerve dys-

function. This was mainly thought to be dependent

on the extent of facial nerve dissection, following the

size of tumor. the average9SD was 26.099.0 in

superficial lobe and 32.3910.5 in deep lobe tumors.

There were no significant differences between super-ficial and deep lobe tumors in terms of sex, age,

histopathology, operation length, and volume of

bleeding. Looking at histological type, the incidence

of postoperative facial nerve paresis was slightly

higher in the patients with pleomorphic adenoma

(32.2%) than in those with Warthin tumor (21.7%).

Warthin tumors mostly develop in the inferior lobe,

so the area of facial nerve dissection is smaller than

in the case of pleomorphic adenomas. This may be

one cause of the low incidence.

The use of an electric knife reduced blood loss.

The mean total blood loss was 39 ml, and in factbleeding was negligible during the cutting of the

parotid gland using the electric knife, resulting in

shortened operation time. The mean operation time

was about 2 h, which consisted of 30 min from skin

incision to the identification of the tragal pointer,

15 min for the identification of the main trunk of the

facial nerve, 30 min for dissection of glandular tissue

and removal of the tumor, and the remaining time

for washing, drain insertion, and suturing.

This technique can be readily performed by

surgeons who are familiar with the use of the electric

knife in surgery for head and neck tumors. All

operating rooms are equipped with electric knives,

while special tools such as bipolar scissors, ultra-

sound scalpel, water-jet dissection, and diathermy

scissors are not provided by every institution. No

special apparatus is necessary for this technique.

Facial nerve monitoring by the electric knife has the

advantage that the distance from the knife to the

nerve can be checked continually. Finding the facial

nerve by nerve monitoring and dissecting the tissue

around the nerve with a cold knife instead of an

electric knife leads to multiple minor bleedings,which in turn may obscure visualization of the course

of the nerve. Compared with conventional parotid

surgery, this technique is excellent because of the

low incidence of postoperative transient facial nerve

paresis, slight blood loss, and short operation time.

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