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CASE REPORT
Endoscopic-assisted resection of pleomorphic adenoma
in the accessory parotid gland
Kazuaki Hasegawa, DDS, PhDa, b, Shintaro Sukegawa, DDS, PhDa, c, Sawako Ono, DDS, PhDd,
Midori Ando, MD, PhDd, Akane Shibata, DDS, PhDa, Yuka Sukegawa-Takahashi, DDSa, Ai Fujimura, DDSa,
Tamamo Matsuyama, DDSa, Soichiro Ibaragi, DDS, PhDb, Hitoshi Nagatsuka, DDS, PhDc,
Koichi Mizobuchi, MD, PhDd, Akira Sasaki, DDS, PhDb, and Yoshihiko Furuki, DDS, PhDa
Department of Oral and Maxillofacial Surgery, Kagawa Prefectural Central Hospital, 1-2-1, Asahi-machi, Takamatsu, Kagawa 760-8557,
Japan, bDepartments of Oral and Maxillofacial Surgery, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical
Sciences, Okayama, Japan, cDepartment of Oral Pathology and Medicine, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan, dDepartment of Pathology, Kagawa Prefectural Central Hospital, Takamatsu, Kagawa, Japana

Abstract : Background : An accessory parotid gland (APG) is a common anatomical structure that occurs in 10%–56% of individuals. Pleomorphic adenomas are the most common benign tumors of the APG, and their ideal
treatment is surgical excision, although there is a risk for aesthetic disorders and facial nerve damage due tothe site of origin. Moreover, despite being benign, these tumors are known to recur. Therefore, it is necessary
to achieve both reliable excision and avoidance of facial nerve damage. Case presentation : We report a case of
a 49-year-old Japanese man with a mass in his left cheek. The lesion was diagnosed as a benign salivary glandtumor derived from the APG by computed tomography imaging, magnetic resonance imaging and fine needle
aspiration cytology. We resected the tumor using modified high submandibular incision under the endoscopic-assisted field of view. Discussion and Conclusions : The tumor was less invasive and reliably resected using
an endoscope. In surgical treatment, the endoscopic-assisted technique is very useful to achieve complete tumor
resection and prevent relapse while avoiding serious complications due to surgical procedures. J. Med. Invest.
68 : 376-380, August, 2021
Keywords : Endoscopy, Pleomorphic adenoma, Accessory parotid gland, Minimally invasive surgery

BACKGROUND
An accessory parotid gland (APG) is a common anatomical
structure that occurs in 10.2%–56% of individuals (1, 2). The
type of APG lesions is similar to that of parotid gland lesions,and 1%–8% of all parotid gland lesions are derived from the
APG (3). Tumors of the parotid gland and APG can be differentiated on the basis of whether continuity can be detected between
the tumor and the parotid gland (4).
Pleomorphic adenomas are the most common benign salivary
gland tumors, especially in the parotid gland, and their ideal
treatment is surgical excision. Extracapsular dissection using
the external preauricular incision approach is sufficient to treat
the majority of pleomorphic adenomas in APG, and the conventional transcutaneous excision approach is a well-establishedsurgical technique for complete resection of these lesions (5).
However, this method has the major complication of leaving
large scars on the facial area.
In recent years, various endoscopic-assisted surgeries havebeen reported in the field of head and neck surgery (6). A safe
surgery requires a large incision, but postoperative scarring
becomes serious. Small incisions made to reduce scarring cancompromise the safety of surgery. Endoscopic-assisted surgery
has become widespread to solve this paradox. Maintaining
a good surgical field of view is important to avoid damage to
List of abbreviations
APG, Accessory parotid gland
FNA, Fine needle aspirationcommonly important anatomical structures such as the nerveand blood vessels. This surgical procedure approached from asmall incision has expanded the surgical field of view throughthe magnifying field of view effect of the endoscope and also
strengthened minimally invasive and safe surgery (7).
We report a case study in which reliable and minimally invasive treatment for a pleomorphic adenoma in the APG was
performed via endoscopic-assisted surgery.

CASE PRESENTATION
A 49-year-old Japanese man had a history of a painless mass
in his left cheek, which had been slowly growing in size over the
past 6 months. He was referred to our department at Kagawa
Prefectural Central Hospital in 2019 by his local dentist. He had
no medical or family history and was healthy.
Extraoral examination revealed a round, painless mass measuring 30 × 25 mm in diameter with no pulsation located anterior to the left masseter muscle and directly inferior to thezygomatic buttress. The mass was not tender and did not change
in size during mandibular movements or the Valsalva maneuver. The overlying facial skin was normal, and no adenopathy
was noticed. (Fig. 1. a, b) The patient had no history of trauma
and surgery in that region. Intraoral examination showed good
Received for publication March 15, 2021 ; accepted May 14, 2021.
Address correspondence and reprint requests to Sukegawa Shintaro,
Department of Oral and Maxillofacial Surgery, Kagawa Prefectural
Central Hospital, 1-2-1, Asahi-machi, Takamatsu, Kagawa 760-8557,
Japan and Fax : +81 87 802 1188.

The Journal of Medical Investigation Vol. 68 2021

The Journal of Medical Investigation Vol. 68 August 2021
saliva flow with firm palpation of the mass in question. It was notpossible to palpate the mass from the oral cavity.
A computed tomography scan disclosed a well-demarcatedround mass lesion within the left APG. (Fig. 1. c, d) Magnetic
resonance imaging revealed a lobulated ovoid mass measuring 31 ×
26 × 25 mm with well-defined margin in the left APG. (Fig. 1. e)
The lesion showed isointense signals on T1-weighted sequences
and a high signal on T2-weighted sequences. (Fig. 1. f) Sample
collection using fine needle aspiration (FNA) was appropriate andsuggested a benign tumor of the salivary gland. On the basis of thefindings of imaging and tissue biopsy, the preoperative diagnosis
was a pleomorphic adenoma derived from the APG.
The patient intended to undergo surgical resection in the mostaesthetic manner possible. Considering the benign nature of
the tumor, we decided that the high submandibular approach,which is often used in oral and maxillofacial surgery in recent
years for diseases of the temporomandibular joint, should be
combined with endoscopic resection. Surgical excision was performed through an endoscopic-assisted technique under generalanesthesia. A skin incision measuring approximately 6 cm inlength was made along the retromandibular space via the highsubmandibular approach. The scalp flap was raised, and a mo-

Fig 1. Patient presenting with a swelling of the left mid-cheek area(a, b) Front and side facial photos. (c, d) Coronal and axial imagesof computed tomography scans showing a tumor outside the left
masseter muscle, with no involvement between the tumor and thezygomatic bone. (e) T2-weighted magnetic resonance images showingthat the tumor is covered with a thick capsule but partially penetrates
the masseter muscle. (f) Fat-suppressed T2-weighted images showingthat the tumor is lobulated and internally heterogeneous.

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nopolar ablation and right-angled retractors were used to expose
the superficial layer of the parotid gland via the masseter muscle, exposing the entire flap. The next step was to identify theconnective tissue around the tumor. Detachment was performed
from the surrounding tissue to remove the tumor, including thecapsule. In addition to the direct field of view, the endoscopic
auxiliary field of view was useful. In particular, the part of thetumor in contact with the masseter muscle was suitable for safe
and minimally invasive surgery in the magnified surgical fieldusing the endoscope. A 30° angle, 4-mm Karlstorz endoscopewith a cold light source was inserted and replaced to a 70° angle
as needed. (Fig. 2)

Fig 2. Intraoperative and endoscopic photographs(a) Intraoperative view of the pleomorphic adenoma through apreauricular and high perimandibular approach using an endoscopicassisted technique. (b) The surgeon and assistants share the same
surgical field through the endoscopic monitor. (c, d) The tumor (*) andthe buccal branch of the facial nerve (arrowhead) are safely separated
in the endoscopic visual field.

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K. Hasegawa, et al. Endoscopic resection of pleomorphic adenoma

Histopathological examination showed proliferation of spindle
myoepithelial cells with hyalinizing stroma. (Fig. 3a) In somearea, there is ductal structure lined by epithelial cells. (Fig. 3b).
The tumor composed of both myoepithelial and epithelial cells,
the diagnosis of pleomorphic adenoma was made. The tumor was
surrounded by a thick fibrous capsule and contained preexisting
salivary gland tissue at some edges. Margin assessment of thecapsule revealed an intact tumor capsule with no evidence oftumor penetration. The postoperative clinical course was good,
and there were no indications of temporary nerve paralysis. At
one year after the operation, the course is good without recurrence, and there are no aesthetic discomforts.

DISCUSSION
APGs are independent of the parotid glands themselves, positioned anterior to them, and superior to the masseter muscle(2, 8). The APG is a common structure, and tumors that occur
in the APG are consistent with tumors of the parotid gland.
Tumors that should be differentially diagnosed from APG tumors are those developing in the cheek region, including benign
tumors such as schwannoma, dermoid cyst, and lipoma, as wellas tumors of the lymph node and masseter muscle, Stensen’s
duct primary tumors, minor salivary gland–derived tumors,and aberrant salivary gland tumors. The histological subtypesof these tumors can be differentiated according to histopathological findings (4). FNA is a commonly performed diagnostic
test in the initial evaluation of a parotid mass. The advantage ofthis technique is that it can be performed in the outpatient setting with minimal recovery time and low risk of complications.
However, a potential disadvantage is that it has been associatedwith variable sensitivity and specificity in distinguishing malignant from benign disease. Moreover, high rates of nondiagnostic
aspirations have been reported in the literature (9). FNA of theparotid gland has moderate sensitivity and high specificity indifferentiating malignant from benign disease. Given the highpositive likelihood ratio, a positive FNA finding can predict thepresence of malignancy with 98%–100% accuracy, depending on
the prevalence of the malignancy (10). In our case, sampling via
FNA was appropriate and suggested a benign tumor of the salivary gland with no malignant findings. We diagnosed the tumor
as a pleomorphic adenoma in the APG based on histological andimaging findings and the frequency of occurrence.
Pleomorphic adenomas account for up to two-thirds of allsalivary gland neoplasms, especially in the parotid gland (11).
Although this tumor occurs in individuals of all ages, it is mostcommon in the 30–60 years age group and gender differences are
more common in female (12). Treatment of this tumor is no longer enucleation in contemporary surgical practice, and partial or
total parotidectomy or extracapsular dissection is the operationof choice at initial presentation (13). Pleomorphic adenomas havea low risk of recurrence. After superficial parotidectomy, the recurrence rate may be approximately 2% (14). Tumor-associatedfactors that may affect recurrence include its size, histopathological subtype, satellite nodules, and inadequacy of encapsulation.
Surgery-associated recurrence factors include tumor leakage,
infiltrated edges, or both. Recurrent pleomorphic adenomas canpose a treatment challenge because the operation is difficult, thetumor is often multinodular (15), and it can be associated withcompromise of the facial nerve. Furthermore, the risk for malignant transformation after recurrence is 3.3% (16). Therefore,
reliable excision of the tumor is essential.
The most common conventional approaches for the resection of
benign tumors in the APG are a percutaneous S-shaped incisionsimilar to parotid tumor surgery and a face-lift incision. The
resulting scars may severely affect the postoperative appearanceof the patient (17). Although adequate exposure of the operative
field is achieved in traditional approaches, they are subject toseveral complications, including damage to Stensen’s duct, facial

Fig 3. Gross and histological findings
Gross findings of the resected material(a) The resected tumor was a nodular solid mass measuring 3.2 × 3.0 × 2.5 cm3 in size. (b) The cut surface of the tumor waswell defined and white-to-yellowish-brown in color. The capsule and soft tissue around the tumor were also resected. (c) The
tumor showed predominately myoepithelial cell proliferation with fibrous matrix (100×). (d) In the tumor, proliferation ofglandular cells along with myoepithelial components was also observed (100×).

The Journal of Medical Investigation Vol. 68 August 2021
nerve injury, skin scars, and salivary fistula. A new surgicalmethod using an endoscope has been proposed to improve theseadverse events. Li et al. (17) reported a method of removing pleomorphic adenomas and benign lymphoepithelial lesions within
the APG under complete endoscopic field of view with an incision
along the tragus and two incisions for inserting the endoscope.
Zhang et al. (18) reported an approach of preauricular incision in
the endoscopic-assisted field of view to remove fibromas, hemangiomas, and lymphomas within the APG. A general consensus
is that tumors of the parotid or submandibular gland, especiallypleomorphic adenomas, should be partially excised around theextracapsular tissue (19). Therefore, for pleomorphic adenoma
derived from the parotid gland, high skill is required for endoscopic operation due to the anatomical positional relationship infront of the parotid gland. A modified high submandibular incision is a relatively used approach in the field of oral surgery fortreating fractures of the temporomandibular joint process (20).
To our knowledge, our case study is the first report to demonstrate that a modified high submandibular approach under endoscopic-assisted visual field may reliably resect the tumor andreduce postoperative complications such as facial nerve injury
and scarring.
Endoscopic-assisted surgery can magnify the surgical viewand thus enhance the identification of small vessels, nerves, andother anatomically important structures. Maintaining a goodsurgical view is important to avoid neurovascular damage andinjury of important structures. The reported benefits of thismethod include minimal postoperative scars, improved aesthetic
effects, and quicker postoperative recovery (6). In our case also,
we were able to shorten the incision line and the buccal branchof the facial nerve could be safely detached from the lesion. Usingan endoscope intraoperatively has additional benefits as well.
Surgical field confirmation by multiple operators is possible atthe same time, and they can communicate smoothly. Endoscopes
are also useful for education (21). However, because of the poor
operation space, endoscopic-assisted partial resection aroundthe extracapsular tissue requires a highly skilled technique,which prevents its popularization (22). It is important to use
endoscopes frequently to train surgeons. Complete endoscopic
surgery has also been reported (19), although it is extremely
difficult. The immaturity of the assistant causes prolonged
surgery time and inadequate surgical visual field expansion.
Improving the skills of the first assistant’s endoscopic operationis very important for the success of endoscopic surgery. By adding an endoscopic technique to the approach that oral surgeons
always use, a safer and less invasive surgery can be performed
more easily. The immaturity of the assistant causes prolonged
surgery time and inadequate surgical visual field expansion.
As our measure, we usually have used endoscopes as a team tocreate an environment where young assistants can master theoperation of endoscopes. Actively incorporating endoscopes into
oral surgery is useful not only for patients but also for the futureof oral surgery.

CONCLUSIONS
Although pleomorphic adenomas are benign tumors, theyrequire reliable resection to prevent recurrence. Aesthetic impairment is the major problem in the surgical resection of lesions
originating from the APG and parotid glands. Endoscopic-assisted surgery is advantageous in terms of both reliable tumor
resection and aesthetics.

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CONFLICTS OF INTEREST AND SOURCE OF
FUNDING
None declared.

PATIENT CONSENT
Written patient consent was obtained to publish clinicalphotographs.

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